Agronomy: Principles and Practices of Soil, Water, and Crop Management, Transcriptions of Agricultural engineering

Download Agronomy: Principles and Practices of Soil, Water, and Crop Management and more Transcriptions Agricultural engineering in PDF only on Docsity! 1 Acharya .N.G.Ranga Agricultural University, Rajendranagar, Hyderabad. Course No: AGRO 101 Course Title: Principles of Agronomy and Agricultural Meteorology Credit Hours: 3(2+1) Dr .A. Pratap Kumar Reddy, Associate Professor, Department of Agronomy, College of Agriculture, Rajendranagar. ANGRAU. Dr.V. Radha Krishna Murthy Professor(Academic), ANGRAU,o/o Dean of Agriculture, Administrative Office, Rajendranagar,Hyderabad-30 2 LECTURE NO – 1 DEFINITION OF AGRICULTURE, MEANING AND SCOPE OF AGRONOMY The term agriculture is derived from the Latin words “ager” or “agri” meaning “soil” and ‘cultra’ meaning ‘cultivation’ Agriculture is a very broad term encompassing all aspects of crop production, livestock farming, fisheries, forestry etc. Agriculture may be defined as the art, the science and the business of producing crops and livestock for man’s use and employment. Agriculture is the cultivation of lands for production of crops for a regular supply of food and other needs for progress of the nation. Agriculture is influenced by a large number of factors, some of which can be controlled by man (soil and irrigation) which others are beyond the control (climate) The term “Agronomy” is derived from Greek words “Agros” meaning “field” and “nomos” meaning “to manage” Agronomy is a branch of agricultural science which deals with principles and practices of soil, water and crop management. Agronomy deals with methods which provide favourable environment to the crop for higher productivity. Importance of basic sciences for development of Agricultural science • Basic science is the study of basic principles and fundamentals of the respective subject. • Applied science is the study in which the basic principles and fundamentals of respective subject are applied in a practical field. • Agricultural sciences are essentially applied sciences and are dependent on basic sciences of Botany, Physiology, bio-chemistry, ecology, zoology, chemistry, physics, mathematics, economics etc. For example 1. Knowledge of Botany is helpful in plant breeding and plant genetics and is making possible for evolution of different varieties in crops suitable to particular agro-climatic condition. 2. The knowledge of zoology (basic science of entomology) is helping the farmer to identify the insect pests which are responsible for damage to agricultural produce. 3. Soil chemistry helps in understanding the plant nutrient status in the soil and the deficiency symptoms in plants. 5 Table 1.1 Net irrigated area (m.ha.) under different sources. 1950-51 1990-91 2000-01 2005-06 Canals 8.3 16.9 15.7 15.5 Wells and tube wells 6.0 24.1 33.8 35.4 Tanks 3.6 3.2 2.4 2.0 Others 3.0 3.2 2.9 7.3 Total 20.9 47.4 55.1 60.2 FERTILIZERS: Fertilizers consumption in India 1 1951-52 - 0.07m.t 2 1969-70 - 1.98 m.t 3 2005-06 - 35.45 m.t 4 2006-07 - 38.03 m.t (18.1 – kharif, 19.9 Rabi) Consumption per unit area - 150kg/ha Consumption ratio for N - P - K 8.4 : 2.5 : 1.0 The required N and P fertilizers are produced in our country while K fertilizers are totally imported. PESTICIDES: 1950 - 100t 1996-97 - 92,700t Average use - 429 g/ha Consumption of Pesticides - 2006-07-41515 m. t (India) 6 HYV’S AND HYBRIDS: India witnessed green revolution in 1960,s and 70,s particularly through wheat crop. It is due to dwarfing gene “NORIN”. India also witnessed white revolution with milk. Blue revolution with Aquaculture and partial success of Yellow revolution with oil seeds i. Now it is being programmed for Rainbow Revolution. ii. Apart from traditional breeding programmes, new varieties were evolved using other techniques like use of Radio-isotopes. Biotechnology etc. iii. Now we also have GM plants NON-TRADITIONAL CROPS AND INTROUDUCED CROPS: Rice is grown in Punjab with very good yields and wheat yields are very good in south and Eastern India (Non-traditional areas) Crops like sunflower, Soya bean and oil palm are introduced into India and now occupy considerable area. MECHANIZATION: Cattles are replaced to a great extent by Tractor. 1950-51 NOW Tractors (m) 0.01 2.63 Oil engines (m) 0.07 4.90 Electrical pumps (m) 0.02 9.80 Use of seed drills has picked up. New planting equipments introduced into the country include potato planter, groundnut planter, rice transplanter, sugar cane sett cutter – cum- planter. Now combines are put to use for the harvest of wheat, rice, soya bean and gram. One important obstacle in the way of mechanization in India is the size of operational holding. The average farm size in India is 1.57 ha. In other countries: 1993 ha in Australia 158 ha in USA 55 ha in UK 1.0 ha in Japan WATERSHED PROGRAMMES: Water shed programmes for soil and moisture conservation have been taken up. Anna Hazare in Maharashtra (Ralegaon siddi) Rajendra Singh in Rajasthan Weather forecasting systems are improved due to the use of satellite communications. Particularly the shortage forecast. 7 Agricultural Extension: In A.P DAATT (District Agricultural Advisory and Transfer of Technology) centers and “Rytu Mitra” T.V programmes are educating the farmers about the better management practices. 10 WARDA : West Africa Rice Development Association, Ivory Coast, West Africa IMPORTANCE EVENTS OF AGRICULTURE IN INDIA 1788 First attempt at cotton crop improvement in Bombay province 1827 First agricultural society at Calcutta 1864 First model agricultural farm at Saidapet, Tamil Nadu 1871 Department of Agriculture created 1878 Higher Education in Agriculture at Coimbatore 1880 First Report of Famine Commission (Famine during 1876-77 1893 Second report of Famine Commission 1901 Third report of Famine Commission 1901 First Irrigation Commission 1902 Introduction of large scale cultivation of groundnut 1903 Imperial Agricultural research Institute at Pusa, Bihar 1904 Introduction of Cambodia cotton 1912 Imperial Sugarcane Breeding Station at Coimbatore 1926 Royal Commission on Agriculture 1929 Imperial (Indian) Council of Agricultural Research at Delhi 1936 IARI shifted to Delhi 1942 Grow More Food Campaign 1946 Central Rice Research Institute 1947 Fertilisers and Chemicals, Travancore 1956 Project for Intensification of Regional Research on Cotton, Oilseeds and Millets (PIRRCOM) 1960 Intensive Agriculture District Programme (IADP) 1963 National Seed Corporation 1965 Intensive Agriculture Area Programme (IIAP) 1965 National Demonstration Programme 1965 All India Coordinated Rice Improvement Project, Hyderabad 1966 HYV Programme 1966 Multiple Cropping Schemes 1970 Drought Prone Area Programme 1971 All India Coordinated Project for Dryland Agriculture 1972 ICRISAT 1973 Minikit Trails Programme 1974 Command Area Development 1975 Release of first cotton hybrid in India 11 1976 Report of National Commission on Agriculture 1976 Integrated Rural Development Programme (IRDP) 1977 Training and Visit (T&V) System 1979 National Agriculture Research Project (NARP) 1982 National Bank for Agriculture and Rural Development (NABARD) 1986 Establishment of Technology mission on oilseeds 1993 Release of First rice hybrid in India 1998 National Agricultural Technology Project (NATP) ITDA - Integrated Tribal Development Agency SFDA - Small Farmers Development Agency HADP - Hill Area Development Project Special Programme for Horticultural Crops DRDA - District Rural Development Agency Functions of ICAR: Coordinating Agricultural activity between states and center financing research problems. Maintaining National Research Centers and Institutes Agricultural research is carried out by: ICAR research centers SAUs (State Agricultural Universities) State Government Research Centers Private agencies • (Please find out different agricultural universities in India and their location) 12 LECTURE NO – 4 AGRO-CLIMATIC ZONES OF INDIA Based on the criteria of homogeneity in agro-characteristics such as rainfall, temperature, soil, topography, cropping and farming systems and water resources, the country has been divided into 15 agro-climatic regions. 1. WESTERN HIMALAYAN REGION: This consists of three distinct sub-zones of Jammu and Kashmir, Himachal Pradesh and Uttar Pradesh hills. The region consists of skeletal soils of cold region, podsolic soils, mountain meadow soils and hilly brown soils. Lands of the region have steep slopes in undulating terrain. Soils are generally silty loam with altitudinal variations. They are and prone to erosion hazards and slides and slips are quite common. Rice, maize, millets, wheat and barley are the main crops. The productivity level of all crops is lower than the all India average. Ginger, saffron, many temperature flowers and vegetables are grown in this region. This zone is having highest area (45.3%) under forests. Land use planting based on the concept that land up to 30% slope is suitable for agriculture on terraces, 30-50% slopes for horticulture and silvi-pastoral programmes, and above 50% slopes for forestry is a suggested strategy for development of the region. With the full backing of storage and cold storage facilities for transport, marketing and processing, this region will be able to supply fruits and vegetables to rest of the country. 2. EASTERN HIMALAYAN REGION Sikkim and Darjeeling hills, Arunachal Pradesh, Meghalaya, Nagaland, Manipur, Tripura, Mizoram, Assam and Jalpaiguri and coochbehar districts of West Bengal fall under this region, having high rainfall and high forest cover. Shifting cultivation (Jhum), practiced in nearly one third of the cultivated area, has caused denudation and degradation of soils, with the resultant heavy runoff, massive soil erosion and floods in the lower reaches and basins. Since this area has a high potential for agriculture including forestry and horticulture, a complete package of supply of inputs (quality seeds, saplings, fertilizers and pesticides) coupled with marketing and processing, has to be organized for each sub-zone. 3. LOWER GANGETIC PLAINS The West Bengal – Lower Gangetic Plains region consists of four sub-regions. This zone accounts for about 12% of the country’s rice production. Floods and inundation of fields 15 Rice-wheat system is prevalent. There is need to evolve short duration genotypes and also to diversify of the cropping. Food processing industries should be established in areas where farmers have started taking up cultivation of vegetables and fruit crops. 7. EASTERN PLATEAU AND HILLS The eastern Plateau and Hills region consists of the following sub-regions: I. Sub-region of Wainganga, Madhya Pradesh Eastern Hills and Orissa inland, II. Orissa Northern and M.P. Eastern Hills and plateau III. Chotanagpur North and Eastern Hills and plateau IV. Chotanagpur South and West Bengal Hills and Plateau, and V. Chattisgarh and South-Western Orissa Hills. The soils of the region are shallow and medium in depth and the topography is undulating with a slope of 1 to 10%. Rainfall is nearly 1300 mm. Integrated water shed development approach to conserve soil and rainwater should be strengthened. Tank irrigation is significant for sub-zone 2 and sub-zone 5. Irrigation by tube wells is significant in sub-zone 1. In kharif, 82% of the area is under rice. Most soils are acidic and in some areas application of lime is necessary. Cultivation of crops like redgram, groundnut, and soybean in uplands is to be encouraged. Mustard and vegetables are to be grown in irrigated areas. The rehabilitation of degraded peripheral forests is to be taken up on a large scale. Nearly 30% of the forestland is estimated as degraded. Inland fisheries programme needs to be encouraged. 8. CENTRAL PLATEAU AND HILLS This zone comprises of 46 districts of Madhya Pradesh, Uttar Pradesh and Rajasthan. Irrigation and intensity of cropping are low. The literacy percentage is low and the poverty ratio is high. Per capita availability of land is very high (0.446 ha). Since 75% of the area is rainfed, a watershed management programme is to be implemented. Food crops should be replaced by oil seeds. 9. WESTERN PLATEAU AND HILLS This zone comprises of major parts of Maharashtra, parts of Madhya Pradesh and one district of Rajasthan and is divided into four sub-zones. This region forms a major part of peninsular India, with an annual average rainfall of 904 mm. Net sown area is 65% and only 12.4% area is irrigated. Sorghum and Cotton are the major crops in nearly half of the cultivated area. 16 This zone is known for the best quality oranges, grapes and bananas. The area under fruit crops is about one lakh hectares. Farmers are adopting sprinklers and the drip methods of irrigation, particularly, for fruit and vegetable crops. 10. SOUTHERN PLATEAU AND HILLS: This zone comprises of 35 districts of Andhra Pradesh, Karnataka and Tamil Nadu, which are typically semi-arid zones. Rainfed farming is adopted in 81% of the area and the cropping intensity is 111%. Low value cereals and minor millets predominate in the cropping systems. The adoption of proven dryland technology in the watershed areas should aid agriculture in this area. Crop diversification has to be intensified and crops that require less moisture should be preferred. Poultry has developed quickly in many areas of the zone. 11. EAST COAST PLAINS AND HILLS: This zone consists of six sub-zones i) Orissa coastal ii) North Coastal Andhra and Ganjam, iii) South Coastal Andhra, iv) North Coastal Tamil Nadu, v) Thanjavur and vi) South Coastal Tamil Nadu. Rice and groundnut are the important crops. Nearly 70% of the cultivated area does not have irrigation facility and, therefore, a watershed management programme can be taken up to 6.45 m. ha. Tanks account for nearly 20% of the irrigated area in the zone and programmes such as desilting tanks, strengthening of bunds and structures and improvement of field channels need to be taken up through a community approach. Drainage programmes, particularly in the south coastal Andhra Pradesh (Krishna – Godavari delta) and Cauvery delta areas are a vital need, because water logging is a critical constraint affecting crop yields. Alkaline-saline soils in the region total up to 4.9 lakh hectares. Area under waste lands estimate to 25.33 lakh ha. Waste land development programmes should be given priority. The zone with over 2,000 km of coastline and many inland waterways is suitable for fisheries. Brackish water fisheries and aquaculture hold great promise in this area. Roughly 40% of the marine potential is taken advantage of in Andhra Pradesh and 46% in the Tamil Nadu Coast. 17 12. WEST COAST PLAINS AND GHATS: This zone runs along the west coast, covering parts of Tamil Nadu, Kerala, Karnataka, Maharastra and Goa with a variety of crop patterns, rainfall and soil types. This is an important zone for plantation crops and spices and fisheries. Literacy is the highest in Kerala and so is unemployment. Cropping intensity is 124%. Productivity of rice and millets is low and there is need for diversification to horticulture crops such as Mango, Banana and Coconut. Fruit marketing and processing should be systematized by developing appropriate infrastructure. The approach of homestead (group farming) system (one of the agro-forestry systems) of reclaiming and using khar lands (saline soils) or pokhali lands (acidic soils) needs to be planned and implemented. This zone is important for multi-storeyed cropping. 13. GUJARAT PLAINS AND HILLS: This zone consists of 19 districts of Gujarat classified into seven sub-zones. The zone is arid with low rainfall in most parts and only 22.5% of the area is irrigated, largely through wells and tube wells. Only 50% of the cultivated area is under food crops resulting in food deficit. However it is an important oilseed zone. The cropping intensity is 114% and nearly 60% of the zone is considered drought prone. The major thrust should be on rainwater harvesting, dry farming and canal and ground water management. The long coastline and river deltas should be used fully for developing marine fishing and brackish/backwater aquaculture. 14. WESTERN DRY REGION This region comprises of nine districts of Rajasthan and is characterized by hot sandy desert, erratic rainfall, high evaporation, no perennial rivers and scanty vegetation. The ground water is deep and often brackish. Famine and drought are common features forcing people and animals to migrate to other places in search of water, food and fodder. The land-man ratio is high (1.73 ha/person). The average annual rainfall is only 395 mm with wide fluctuations from year to year. The forest area is only 1.2%. The land under pastures is also low (4.3%). The cultural waste and fallow lands are substantial, accounting for nearly 42% of the geographical area. The net irrigated area is only 6.3% of the net sown area. Cropping intensity is 105%. Pearl millet, cluster bean (guar) and moth are the lead crops in kharif and wheat and gram in rabi, but the yield levels per hectare are low. Any change in the cropping pattern is not advocated because of the fodder value of the crops. The acute shortage of fuel, fodder and forage warrants stringent efforts for development of silvipastoral systems and energy NINE AGRO-CLIMATIC ZONES OF ANDHRA PRADESH Fig: 5.1 Agro-Climatic Zones of Andhrapradesh 20 Legend [EE Northem Telangana Zone (Centra! Telangana Zone [EE Southern Telangana Zone [1] Searce Rainfall Zone HEB southem zone [EJ north coastal Zone [EE codavarizone HEB itrisnns Zone HEB High Attitude Zone 21 largely exploited. The net sown area is 2.3 m. ha. and the cropping intensity is 179%. Rice is the principal crop grown and this zone is called as the rice bowl of the state with 43% of total area and production. Other important crops are pulses (blackgram, greengram, redgram), sugarcane, seasmum, tobacco, chillies, cotton and banana. Mango is a widely cultivated horticultural crop of the zone. Cropping is extensively seen during both Kharif and rabi seasons. Water congestion, impeded drainage, development of salinity, heavy rains and cyclones at the time of harvest are the major constraints of crop production. II.NORTH COASTAL ZONE This zone consists of major parts of Srikakulam, vizianagaram, Vishakhapatnam districts and upland belt of East Godavari. The zone consists of 106 mandals and is primarily agrarian in character, with about 54% of its geographical area under cultivation. Geographical area of the zone is 1.8 m. ha., gross cropped area is 1.19 m. ha. and cropping intensity is 117%. The normal rainfall of the zone is about 1060 mm, out of which 61% is received during south-west monsoon, 26% during north-east monsoon and the remaining 13% during winter and summer months. The soils of the zone are predominantly red with clay base accounting for 90% of the area. Alluvial, coastal sand and lateritic soils also occur in this zone. Tanks and canals are the main source of irrigation and 45% of cropped area is irrigated. The important crops raised in the north coastal zone are rice, millets, sugarcane, groundnut, gingelly and mesta. Rice is the principal food crop grown in more than 90% of the irrigated area followed by sugarcane. All the other crops are grown under rainfed conditions. III. SOUTHERN ZONE The Southern zone consists of the districts of Nellore, Chittor and parts of Kadapa and Anantapur, covering a total geographical area of 4.35 m. ha. The climate of the zone is dry tropical. The average annual rainfall ranges from 700-1050 mm. About 50% of the rainfall is received during SW monsoon. Nellore district receives 60% rainfall during NE monsoon. The soils of the zone are predominantly red loamy, shallow to moderately deep with limited occurrence of heavy textured black soils. Gross cropped area is 1.87 m. ha. Tanks and wells are the main source of irrigation with 46% of cropped area under irrigation and cropping intensity is 108%. The principal crops cultivated in the zone are groundnut and rice with cultivation of sugarcane, ragi, bajra, redgram and other pulses limited to localized areas. Area under millets particularly bajra and sorghum is declining giving way to sunflower. Citrus, melons and mango also are grown extensively in some parts of the zone. IV. NORTHERN TELANGANA ZONE This zone has a total geographical area of 7.43 m. ha. covering the districts of Adilabad, Karimnagar, Nizamabad, parts of Medak, Nalgonda, Warangal and Khammam. The climate is typically tropical rainy. The mean annual precipitation ranges from 900 to 1150 mm with 82% of rainfall from SW monsoon. The net sown area is 2.21 m. ha. of which 0.67 m. ha. is irrigated representing 30.3% of the net sown area. The major crops grown in the zone are rice, sugarcane, jowar, pulses, maize, 22 cotton, groundnut, turmeric and chillies and others. Cropping intensity is 110%. Wells are the main source of irrigation followed by canals. Red chalka soils are predominant. V. SOUTHERN TELANGANA ZONE The zone comprises of the districts of Rangareddy, Mahabubnagar (except the southern border), Nalgonda (except south east border), north western part of Warangal and southern part of Medak districts. The zone covers an area of 4.0 m. ha. The soils of the zone are mainly red sandy, red earths and medium black soils. The zone receives an annual normal rainfall of 809 (700-900) mm. About 77% of total rainfall is received during SW monsoon only 14.35% of the 1.68 m. ha. of net sown area is under irrigation. The principal crops grown in the zone are jowar, castor, rice groundnut, bajra, redgram, horsegram, ragi, greengram, maize and seasmum. It is the castor belt of A.P. VI. SCARE RAINFALL ZONE The zone consists of 145 mandals distributed in Kurnool and parts of Anantapur, Kadapa, Prakasam and Mahbubnagar districts covering an area of 4.77 m. ha. The zone is mostly undulated with mountains, hills and plain areas. Predominant soils of the zone are black soils. Other soils are red earths with loamy sub-soil, red sandy soil and problem soils. The soils in Anantapur districts are shallow with low fertility. The zone is mainly characterized by frequent droughts with lowest rainfall in the state (500 – 750 mm). The rainfall is also uncertain and erratic and 56% of rainfall is from SW monsoon. Major area in the zone is rainfed and irrigated area is only 15.4%. The major crop of this zone is groundnut occupying about 33.4% of total cropped area of 2.13 m. ha. Other important crops include sorghum, foxtail millet, rice, cotton, coriander and pearl millet. Cropping intensity is 109% very good dryland agriculture technology. VII. HIGH ALTITUDE AND TRIBAL AREA ZONE This zone is comprised of 40 Mandals distributed in parts of Srikakulam, Vishakhapatnam, East Godavari and Khammam districts covering a geographical area of 1.8 m. ha. The area of this zone lies between 50 to 1680 m AMSL and is characterized by high slopes, mountains, hills and hillocks as part of Eastern Ghats. Red soils are the most predominant type (94.8%). A small area is covered under alluvial soils and coastal sands. The mean annual rainfall ranges from 1245 to 1288 mm of which about 70% is contributed by south-west monsoon. Large geographical area (58.9%) in the zone is under forests and the net cropped area is only 19.2% with very little irrigation sources. The tribal people of this area practice shifting cultivation locally known as “podu” cultivation for their subsistence. Rice is the most important crop in the zone occupying 36.2% of the gross cropped area of 0.42 m. ha. The other principal crops growth are millets, mesta, niger and tuber crops. Tea, coffee and other plantation crops are also grown in addition to aromatic and medicinal plants. Cropping intensity is 120%. Forest produce such as honey, gum, soap nuts, tamarind fetch income to the tribal people. 25 Effects of Tillage on soil physical properties: 1. Soil Structure: Arrangements of soil particles with crumbly and granular nature is considered good. Best size of soil aggregate for good growth of crop is (1-5mm) smaller aggregates may clog soil pores and larger ones may have large pore space. Tillage improves soil structure when done at optimum soil moisture level. Tilling a soil when it is too wet spoils the structure. Ploughing a dry soil is difficult and will not help in improving structure. 2. Soil texture: Relative proportion of different soil particles namely sand, silt and clay. Coarse sand - 2.0 - 0.2mm. Fine sand - 0.2 - 0.02mm. Silt - 0.02 - 0.002mm. Clay - <0.002mm. • Tillage has no effect on soil texture. 3. Pore space: When a field is ploughed the soil particles are loosely arranged and pore space is increased. When the soil is in good tilth the capillary and non capillary pores would be roughly equal. This facilitates free movement of air and moisture in soil. 4. Bulk Density: (B.D) When the soil is loosened, the soil volume increase without any affect on weight. BD of Clay soils is low (1.05 m3 and that of sandy soils is high (1.25 – 1.30 m3) and Bulk density of tilled soil is less than that of untilled soil. Particle density is always more than BD. 5. Particle density: Particle density is not altered by tillage. 6. Soil Colour: Organic matter is mainly responsible for the dark brown to dark grey colour of the soil. Tillage increases oxidation and decomposition of organic matter resulting in fading of colour. 26 LECTURE NO-7 TYPES OF TILLAGE – PREPATORY TILLAGE – FACTORS AFFECTING PREPARATORY CULTIVATION, AFTER CULTIVATION, PUDDLING Tillage operations are grouped into two types based on the time at which they are carried out. 1. Preparatory cultivation – which is carried out before sowing the crop 2. After cultivation – That is practiced after sowing the crop. → Primary tillage – Ploughing → Secondary tillage – harrowing → Seed bed preparation – country plough can be used. Factors influencing preparatory tillage: 1. The previous crop grown: Stubble of previous crop influence the tillage (Redgram, cotton stubbles are very deep rooted and require deep tillage to remove them) 2. The crop to be grown: Crops like sorghum can be grown with rough tilth for very small seeded. Crops like tobacco, chilles etc fine tilth is required. Deep tillage is required for crops like tuber crops and sugarcane. 3. Types of soil: Clay soil can be ploughed only with in a narrow range of soil moisture and the power or drought required is high. Light textured soils can be ploughed under a wide range of soil moisture and require less drought. 4. Climate: Deep tillage is not permitted in shallow soils in low rainfall areas as it leads to rapid drying and loss of stored soil moisture. Deep cultivation is possible in high rainfall areas. 5. Type of farming: Intensive cropping requires intensive tillage. Intercultivation: Tillage operations done between the crop rows with the objectives of • Destroying the weeds • To form a soil mulch • To prevent cracking of soil • To prevent crust formation 27 Intercultivation starts from very early stage of crop i.e., two to three weeks from sowing. Short duration crops require two-three intercultivation while long duration crop require 3-4 weeks. After cultivation: It includes intercultivation and various other special operations carried out in a standing crop. They include. 1. Thinning and Gap filling. 2. Rogueing in crops for seed purpose. 3. Earthing up in crops, sugarcane, banana, and groundnut. 4. Cropping in banana 5. Desuckering oper in banana 6. Wrapping and propping in sugarcane 7. Nipping in castor 8. Topping, Trimming and desuk in tobaccor basal leaves are removed 9. Defoliation in cotton 10. Hand pollination in sunflower. Fertilizer app in irrigation also comes under after cultivation. PUDDLING Rice growth and yield are higher when grown under submerged conditions. Maintaining standing water throughout the crop period is not possible without puddling. Puddling is ploughing the land with standing water so as to create an impervous layer below the surface to reduce deep percolation losses of water to provide soft seedbed for planting rice. Puddling operation consists of ploughing repeatedly in standing water until the soil becomes soft and muddy. Initially, 5cm to 10 cm of water is applied depending on the water status of the soil to bring it to saturation and above and the first ploughing is carried out. After 3 to 4 days, another 5 cm of water is applied and later after 2 to 3 days second ploughing is carried out. By this operation, most of the clods are crushed and majority of the weeds are incorporated. Within 3 to 4 days, another 5 cm of water is given and third ploughing is done in both the directions. The third ploughing can be done either with a wetland plough or with a wetland puddler. Planking or levelling board is run to level the field. To know whether puddling is thorough or not, a handful of mud is taken into the hand and pressed. If it flows freely through fingers and if there are no hard lumps, puddling is considered to be thorough. Unlike in other tillage operations, puddling aims at destroying soil structure. The individual soil particles viz., sand, silt and clay are separated during puddling operation. The soil layer with high 30 METHODS OF SOWING Direct seeding Transplanting Broad casting Line sowing Drilling Dibbling Time of sowing: 1. Sowing very early in the season may not be advantageous. Eg: sowing rainfed ground nut early may result in failure of crop if there is prolonged dry spell from the 2nd week of june to 2nd week of july. 2. Delayed sowing invariably reduces yields a. Eg: rainfed sorghum yields are reduced due to delay in sowing beyond June reason – sorghum sown late is subjected to severe atlack of shoot borer. b. Eg: In rainfed groundnut sowing beyond July reduced the yields of all varieties at tirupathi. 3. Advancing sowing of Rabi sorghum. From November-September to October. Increase the yields considerably as more moisture would be available for early sown crop. 4. Sowing the crop at optimum time. Increases yields due to suitable environment at all the growth stages of the crop. 1. Optimum time of sowing for Kharif crop – June or July 2. Optimum time for Rabi crop - last week of October to first week of November 3. Summer crop - First fortnight of January. Depth of Sowing: Uneven depth of sowing results in uneven crop stand. • Plants will be of different sizes and ages and finally harvesting is a problem as there is uniformity in maturity. • The thumb rule is to sow seeds to a depth approximately 3-4 times their diameter. 31 • The optimum depth of sowing for most of field crops ranges between 3-5 cm • Shallow depth of sowing of 3-5 cm is enough for small seeds like sesamum finger millet and pearl millet. • Very small seeds like tobacco are placed at a depth of ICM. Bold seeded crops like castor, groundnut, cotton, and maize etc. 6-7 cm. Seed rate: 1. Tobacco - 30g per hector 2. Mustard - 2-3 Kg/ha 3. Pulses - 10-12Kg/ha 4. Soybean - 80-100 Kg/ha 5. Groundnut - 100-120 Kg/ha 6. Forage grasses (rooted slips) - 2-3 tons/ha 7. Potato tubers - 5-7 tons/ha 8. Sugarcane (selts) - 7 tons/ha 32 LECTURE NO – 9 CROP STAND ESTABLISHMENT – FACTORS AFFECTING OPTIMUM STAND ESTABLISHMENT It is influenced by various Factors: 1. Quality of seed – purity, germination percent viability, free from dormancy, free from seed borne diseases, etc 2. Seed treatment: a. Fungicidal treatment – mainly to avoid seed borne and also soil borne diseases –Thiram, Captan, Mancozeb, Carbendazim, etc. used as per recommendations. b. Pesticide treatment – Malathian for control of scale insects in sugarcane, Quinolphos for stem borer of rice. c. Hot water treatment – 520C for 30 minutes to control red rot and smut diseases in sugarcane. d. Special treatments – dung treatment or acid treatment (100 ml conc. H2SO4/kg seed) of cotton for removing fuzz (for sowing by using seed drills, so that the seeds do not cling to each other in the seed tube) e. Scarification – Rubbing against hard surface to soften the hard seed coat (e.g: castor) or to remove the glumes covering the seed (eg: stylo) or soaking in water for 12-24 hrs. (Eg: rice, stylo) splitting the seeds into locules (e.g.: coriander) or compound bulbs into individual cloves – (e.g: garlic). f. Breaking dormancy – GA., cytokinins, Ethelene (500ppm for 12hrs) g. Mixing seed with other materials to increase the bulk in case of small seeded crops, mixing with sand or soil in case of crops like Sesamum, Lucerne, mustard, ragi, etc. h. Removal of broken kernels, ill filled seed – eg: Groundnut. i. Rhizobium treatment – in case of legumes – specific Rhizobium cultures are available depending upon the crop. These are helpful in fixing atmospheric – N. use 125g. jaggery in 1 litre of water – boil – cool – add Rhizobium culture (500g) and then thoroughly mix with seed (for 1 hour) and shade dry before sowing (R.japonicum, R.melitotus. are some examples) 3. Seed bed preparation Coarse tilth for groundnut, redgram, etc Fine tilth for ragi, mustard, etc 4. Time of sowing – important to meet the climatic requirements of each crop. This is very important in rain fed crops. In case of late sowing (maturity may coincide with drought), pest and disease incidence may be more and may affect 35 Plant population and growth • High plant density brings out certain modifications in the growth of plants. • Plant height increases with increase in plant population due to competition for light. • Sometimes it may happen that moderate increase in plant population may not increase but decrease plant height due to competition for water and nutrients but not for light. • Leaf orientation is also altered due to population pressure. The leaves are erect narrow and are arranged at longer vertical intervals under high plant densities. This is a desirable architecture. Plant population and yield • Decrease in yield of individual plant at high plant density is due to the reduction in the no. or earls or panicles. • Ex: - Redgram produces about 20 pods per plant at 3.33 lakh plants/ha (30x10cm) while it produces more than 100 pods per plant at 50,000 plants/ha (80x25cm). • Under very high population levels plant become barren, hence optimum plant population is necessary to obtain maximum yield. Optimum plant population Optimum plant population for any crop varies considerably due to environment under which it is grown. It is not possible to recommend a generalized plant population since the crop is grown in different seasons with different management practices. E.g.:- Redgram plants sown as winter crop will have half the size of those grown in monsoon season. Optimum plant population is 55,000 plants/ha. For monsoon season crop of redgram and this is increased to 3.33 lakh plants/ha for winter crop; as low temperature retards the rate of growth, higher population is established for quicker ground cover. In sorghum, when the climate is favourable during pre-anthesis period, the optimum population is two lakh plants/ha and when it is not congenid for growth during pre-anthesis, it is four lakh plants/ha. PLANTING PATTERN Planting pattern influences crop yield through its influence on light interception, rooting pattern and moisture extraction pattern. Different planting patterns are followed to suit different weed control practices and cropping systems. Plant geometry refers to the shape of plant while crop geometry refers to the shape of space available for individual plants. Crop geometry is altered by changing inter and intra-row spacing. 36 Square planting It is reasonable to expect that squares arrangement of plants will be more efficient in the utilization of light, water and nutrients available to the individuals than in a rectangular arrangement. In wheat, decreasing inter-row spacing below the standard 15-12 cm i.e., reducing rectangularity, generally increases yield slightly. In crops like Tobacco, intercultivation in both directions is possible in square planting and helps in effective control of weeds. However, square planting is not advantageous in all crops. Groundnut sown with a spacing of 30x10cm (3.33 lakh/ha) gave higher pod yield than with same amount of population in square planting. Pod yield is reduced either by increasing rectangularity or approaching towards square planting. Rectangular planting Sowing the crop with seed drill is the standard practice. Wider inter-row spacing and closer intra-row spacing is very common for most of the crops, thus attaining rectangularity. This rectangular arrangement is adopted mainly to facilitate intercultivation. Sometimes only inter-row spacing is maintained and intra-row spacing is not followed strictly and seeds are sown closely as solid rows. Miscellaneous planting arrangements Crops are sown with seed drills in two directions to accommodate more number of plants and mainly to reduce weed population. Crops like rice, finger millet are transplanted at the rate of 2-3 seedlings per hill. Transplanting is done either in rows or randomly. Skipping of every alternate row is skipped, and the population is adjusted by decreasing intra-row spacing, it is known as paired row planting. It is generally restored to introduce an intercrop. 37 LECTURE NO-11 SOIL FERTILITY – SOIL FERTILITY AND SOIL PRODUCTIVITY – FERTILITY LOSSES – MAINTENANCE OF SOIL FERTILITY – SOIL ORGANIC MATTER The inherent capacity of the soil to supply plant nutrients in adequate quantities and in suitable proportions is termed as Soil fertility. Soil productivity refers to the capacity of a soil to produce crops. A productive soil must be fertile, but a fertile soil must be fertile, but a fertile soil may not be productive. Soil productivity is influenced by 1. Soil fertility 2. Physical condition – depth, structure, texture 3. Activity of soil micro organisms 4. Soil moisture 5. Inhibitory factors like acidity, alkalinity, salinity, water logging, etc. It is necessary to add plant nutrients to the soil periodically. Nutrients are lost from the soil in the following ways 1. Removal by crop (in kg/ha) Crop N P K Rice 90-100 20-25 130-150 Wheat (dwarf) 150-200 80-100 200-300 Sorghum 50-60 20-25 80-100 Maize 100-120 40-50 100-120 2. Removal by weeds 3. Leaching losses – (more in sandy soils) 4. Loss through erosion 5. Loss in gaseous form (N – by denitrification and Volatilization) 40 Soil organic matter: Any material of plant or animal origin found in the soil is known as Organic matter. Organic matter that is well decomposed and digested by many kinds of soil micro organisms and converted into fairly stable, amorphous, brown to black material is termed as “Humus”. It is very difficult to identify the parent material from which it is derived. Uses of Organic Matter: 1. Helps in aggregation of soil particles and improves the structure, permeability and WHC and aeration. 2. It serves as a reservoir of plant nutrients. 3. Organic acids and CO2 produced during decomposition help to dissolve minerals like ‘P’, ‘K’ and make them more available. 4. It helps in maintaining soil pH 5. Leaching of certain cations like K, Ca, Mg, NH4 is prevented because of its higher CEC. 6. It is the source of energy for micro organisms, earthworms and other living things. 7. Helps to maintain soil temperature 8. Alkalinity is reduced. The rate of decomposition of organic matter is dependent on – the activity of soil micro organisms, which in turn is dependent on- 1. Soil moisture content 2. Soil temperature 3. Soil aeration 4. C: N ratio of the original material added. 41 LECTURE NO - 12 WEED CONTROL – DEFINITION OF WEED – LOSSES AND USES OF WEEDS – WEED INFLUENCE ON CROP PRODUCTION – METHODS OF WEED CONTROL First person to use the term weed is ‘Jethro Tull’ 1. A weed is a plant growing where it is not wanted. 2. Weed is an unwanted plant. 3. A plant with –ve value. 4. A plant interferes with intended use of land. 5. A plant growing with desired plant. Losses due to weeds: 1. Weeds compete with crop plants for resource like light, moisture, nutrients. 2. Weeds cause reduction in crop yields. Among the annual agriculture loss in India. Weeds accounts for 45%, insects 30%, diseases 20% others 5%. 3. Weeds increase cost of cultivation. 4. Weeds are alternate hosts for crop pests and diseases. S. No Crop Pest/disease Alternate host. 1. Rice Stem borer Echinochlon sp. 2. Groundnut Stemrot Parthenium 3. Castor Hairy catlepiller Crotalaria 4. Redgram Gram catlerpiller Amaranthus, Datura 5. Weeds reduce the quality of produce. Ex: Cuscuta as an admixture with Lucerne spoils seed quality. • Wild onion and wild garlic as weeds in fodder crops impart off-flavour to milk. Xanthium impairs wool quality of sheep 6. Weeds cause human health problems. • Allergy by Parthenium hysterophorus • Mosquitoes causing malaria. Yellow fever encephalitis and filariasis breed on Pistia and Salvia • Hay fever and asthma caused by Franseria sp. • Dermatitis caused by Amrosia and Helenium 42 Itching and inflammations caused by hair of Urtica sp. 7 Weeds cause animal health problems. • Lantana camara induces hypersensitivity to light. • Rhododendron sp. cause diarrhea and blood strains in milk. • Sorghum halepense poisonous to cattle. 8 Problems of water contamination. • Render drinking water unfit. • Reduce flow of water in irrigation channels • Reduce flow of water in irrigation channels. Ex: Eichornia typha. 9 Reduction in land value, due to Cyperus rotundus and Cynedon, dactylon • Allelopathy: Harmful affects of plant due to research and phytochemicals on other plants. • Avenafatua: Affect germination of weed. Seed exudates. Benefits from weeds: • Constant source of new genes • Saccharum spontaneum is a wild cane used in breeding. • Fodder value • Cynodon dactylon • As leafy vegetables, Amaranths and Celosia. • As Green manures – Tephrosia • Have medicinal value • Leucas aspera – snakebite • Phyllanthus niruri – jaundice • Calotropis – for gastric troubles • Argemona mexicana – skin disorders • Imperata cylindrical – thatching • Cynodon for soil conservation. 45 Based on time of application herbicides are grouped as below: 1. Pre-plant incorporation (PPI) 2. Pre-emergence 3. Post-emergence Based on selectivity: 1. Selective 2. Non-selectivity Based on mode of Action: 1. Systematic 2. Contact Formulations: 1. Wettable powder (WP) 2. Soluble powder (SP) 3. Emulsificable concentrate (EC) 4. Sol concentrates (SC) 5. Granules (GR) 6. Fumigants Based on methods: 1. Foliage application 2. Blanket application 3. Direct spray 4. Protected spray 5. Spot treatment Soil Application: • Surface application • Sub surface layering • Broadcast and band placement • Fumigation Formulations • Active ingredients (ai) – Part of the formation i.e., directly responsible for herbicide affect. 46 • Acid equivalent – Part of the formulation that theoretically can be converted into acid. • Herbicides carriers – Water (for spraying) sand (for broadcasting) • Herbicides are available with different trade names. • Why herbicides are not popular in India. 1. Lot of human resource. 2. Large area is rainfed (where effectiveness is uncertain) 3. Lack of awareness 4. Intercropping situations (limited availability of selective herbicides for both the crops) 5. Small holdings with family labour. 47 LECTURE NO - 13 IRRIGATION MANAGEMENT – IMPORTANCE OF IRRIGATION – OBJECTIVES OF IRRIGATION – DRAINAGE AND ITS ADVANTAGES IRRIGATION: Irrigation is the artificial application of water to the soil to supplement the rainfall and groundwater contribution to assist the crop production. Objectives /Importance of Irrigation 1. To supply the moisture essential for plant growth. 2. For better utilization of production factors. (nutrients) 3. To provide crop insurance against short spells of drought. 4. To dilute/washout soluble salts 5. To soften tillage pans 6. Intensive cropping is made possible 7. Timely seedbed preparation and timely sowing. 8. To create favorable microclimate for crop growth. 9. Higher yields as well as stability in production Method of irrigation Depending on soil type slope source of irrigation water, nature of crop methods differs. 1. Surface methods of irrigation a. Flooding b. Boarder strip c. Corrugations d. Check basin e. Ridge and furrow f. Ring or basin 2. Sub- surface methods 3. Sprinkler – system. 4. Drip/trickle irrigation. 5. Quantity of irrigation water depends on rooting depth and water holding capacity of soil. 6. Irrigation water can be quantified through weirs, flumes, orifices, water meters etc. 50 LECTURE NO - 14 CROPPING SYSTEMS – MONOCROPPING – DEFINITION AND PRINCIPLES OF CROP ROTATION – MIXED CROPPING – INTERCROPPING – RELAY CROPPING – MULTISTORIED CROPPING – SOLE CROPPING – SOLE CROPPING AND SEQUENCE CROPPING Cropping pattern: - It means the proportion of area under various crops, at a point of time in a unit area. It indicates the yearly sequence and spatial arrangement of crops and fallow in an area. Decrease keeping the field vacant Cropping System: It is an order in which the crops are cultivated on a piece of land over a fixed period this is cropping system. Monocropping: or Monoculture refers to growing of only one crop on a piece of land year after year. Ex: Rice – Rice (In Godavari belt) Groundnut every year in Anantapur dist. Disadvantage in Monocropping • Improper use of moisture and nutrients from the soil • Control of crop associated pests and weeds become a problem. Crop rotation: It is a process of growing different crops in succession on a piece of land in a specific period of time with an object to get maximum profit from least investment without impairing soil fertility. Principles of crop rotation: 1. The crops with tap roots should be fall by those which have a fibrous root system 2. The leguminous crops should be grown after non leguminous crops. 3. More exhaustive crops should be followed by less exhaustive crop. 4. Selection of crops should be demand based. 5. Selection of crops should be problem based. 6. The crops of the same family should not be grown in succession because the act like alternate hast for insects, pests and disease pathogens. 51 7. An ideal crop rotation is one which provides maximum employment to the family and farm labour, the machines and equipments are efficiently used then all the agriculture operations are done simultaneously. Multiple cropping Growing two or more crops on the same piece of land in one agriculture year is known as ‘Multiple cropping’. It is the intensification of cropping in time and space dimensions i.e., more number of crops with in a year and more number of crops on the same piece of land. It includes intercropping, mixed cropping and sequence cropping. Inter Cropping: It is growing two or more crops simultaneously on the same piece of land with a definite row pattern. Ex: Setaria + Redgram in 5:1 ratio Groundnut + Redgram in 7:1 ratio (a). Additive series (b). Replacement series Mixed cropping It is the process of growing two or more crops together in the same piece of land. This system of cropping is generally practiced in areas where climatic hazards such as flood, drought, frost etc. are frequent and common. Sequence cropping It can be defined as growing of two or more crops in sequence on same piece of land in a farming year. Depending on number of crops grown in an year. It is called double, triple and quadruple cropping involving two, three and four crops respectively. Relay cropping: It is analogous to a relay race where crop hands over land to next crop in quick succession. Ex: Maize – Early Potato – Wheat – Mungo Overlapping system of cropping: In this the succeeding crop is sown in standing proceeding crop thus in this system before harvesting one crop the seeds of next crop are sown. Ex: Maize potato onion bendi in North India. Ratoon cropping: It refers to raising a crop with re growth coming out of roots or stalks after harvest of the crop. Ex: Sugarcane. 52 Fig:14.1 Multi Storeyed Cropping System Multi Storeyed System: Growing of plants of different heights in same field at the same time is termed as multistoreyed cropping. Ex: Coconut – Piper - banana – Pineapple. Difference between intercropping and mixed cropping S. No Intercropping Mixed cropping 1. The main objective is to utilize the space left between two rows of main crop especially during early growth period of main crop. 1. Main objective is to get at least one crop under any climatic hazards (flood, drought or frost) conditions. 2. More emphasis is given to the main crop and subsidiary crops are not grown at the cost of main crop thus there is no competition between main and subsidiary crop. 2. All crops are given equal care and there is no main or subsidiary crop. Almost all the crops compete with one another. 3. Subsidiary crops are of short duration and they are harvested much earlier than main crop. 3. The crops are almost of same duration. 4. Both the crops are sown in rows. The sowing time may be the same or the main crop is sown earlier than subsidiary crop. 4. Crops may be broad casted and sowing time for all the crops is the same. 55 • By using tractor. • By using threshing benches • By using mechanical threshers. • Winnowing – manual or power operated winnowers. • Drying on threshing floor to bring down the moisture in grain to 8-10% • Bagging for storage (bulk storage is also practiced) in mud bins, straw bins, RCC bins etc.) • Rice is consumed as whole cooked kernel. • The cooking quality depends on shape and size (short slender or long slender) and tie amylase content. (Rice is not stickly if amylase content is 37% and protein content 10%. 60% of rice produced in country undergoes Parboiling: It is a hydrothermal treatment foll by drying before milling. During parboiling, gelatinization of starch and disintegration of protein bodies in the endosperm take place and starch and protein expand and fill the internal air spaces. The fiskures and cracks in the endosperm are sealed making the grain hard as a result of which breakage of grain during milling is minimized. • Parboiled rice takes longer time to cook, dehusking is also easy, loss of protein and starch in cooking water is low. Water soluble B Vit’s and other nutrients diffuse into the endosperm hence loss of nutrients is less even after poilishing. Major steps in parboiling: 1. Soaking 2. Steaming 3. Drying 4. Soaking in normal water 5. Steaming is in hot water under pressure 6. Drying is done until the moisture content comes down to 18-20% then keeps for few hours and again dry for 1-2 hours to bring down the moisture content to 14-16%. 7. During milling rice recovery is 65-75%, husk 20-25% bran 5-7%, brokens 2-4% 56 Paddy + Cleaning + Soaking in water (8 h) + Draining + Steaming (20 minutes) + Aerating (3h) and heaping (3h) + Tempering (1h) + Sun drying (2-4 h) + Dried paddy (14% moisture) Fig:15.1Parboiling Milling of dried paddy (raw and parboiled) + Destoner (remove dust, dirt, chaff and stones) + Sheller + Husk Brown rice and unshelled paddy (aspirated through fan box) tL Huller (primary polishing) tL Bran Polished rice + Cone polishing + Bran Head rice + Packaging Fig:15.2 Milling of paddy 57 MAIZE • Cobs harvested at 25-30% moisture dried for 3-4 days • Shelling is done by beating with sticks or by using cattle, tractor or shelters. • Grain is dry up to 10-12% moisture them stored. • For popcorn, harvest at 30-35% moisture in cobs, slow drying of grain in shade and optimum moisture for best popping is 12-14% GROUND NUT • Early harvest results in immature pods, in delayed harvest pods remain in soil • Soil digging is done (mostly with country plough) to lift the plants with pods from the soil hence optimum soil moisture is important at the time of harvest. • Plants are lifted and placed upside down in the field in the form of small circular heeps. After few days (2-3 days) pods are stripped. A simple comb type hand stripper and pedal operated strippers are available. • Moisture content in pods will be 40% at harvest. Dry the pods to bring down the moisture content to less than 10% store the pods. • Storage is in the form of unshelled pods, for seed purpose is stored in earthen pots. SUGARCANE • Duration 10-14 month for maturity • Foliage becomes pale. • Brik of TSS of the central internode is 15-16% this is measured with hand refracto meter. • Sugarcane is harvested with knifes by cutling to the ground level. Leaves are stripped and immature tops are removed, millable cane is used for making sugar or jaggery. • In western countries cane fields are burnt and within 8-10 hours cane is harvest transported and crushed in the mills. • Bullock or power operated crushers are used to extract juice (less than 65%) • Cane used in acidic in nature. • For jaggery making a clarificant – time sucrite or extract of wild vendy (Abutilon indicum) is added to neutralize the juice. • For preparing time sucrite – time is dissolved in water in 1:5 ratios, filtered and added to cane juice. • Juice is boiled at low temperature for better flocculation and the scum is removed later quick boiling at high temperature is done. During boiling jaggery sol. Is put in cold water and there should be quick solidification at that stage stop boiling and pour it into moulds for cooling and final jaggery collection. ***** 60 6 Managing weather abnormalities like cyclones, heavy rainfall, floods, drought etc. This can be achieved by ; a Protection : When rain is forecast avoid irrigation. But, when frost is forecast apply irrigation. b Avoidance : Avoid fertilizer and chemical sprays when rain is forecast. c Mitigation : Use shelter belts against cold and heat waves. 7 Effective environmental protection. 8 Avoiding or minimising losses due to forest fires. Scope of agricultural meteorology In addition to the points mentioned above, the influence of weather on agriculture can be on a wide range of scales in space and time. This is reflected in the scope of agricultural meteorology as detailed below: 1. At the smallest scale, the subject involves the study of microscale processes taking place within the layers of air adjacent to leaves of crops, soil surfaces, etc. The agrometeorologists have to study the struture of leaf canopies which effects the capture of light and how the atmospheric carbon dioxide may be used to determine rates of crop growth. 2. On a broader scale, agrometeorologists have to use the standard weather records to analyse and predict responses of plants. 3. Although the subject implies a primary concern with atmospheric processes the agrometeorologist is also interested in the soil environment because of the large influence which the weather can have on soil temperature and on the availability of water and nutrients to plant roots. 4. The agro meteorologist also be concerned with the study of glass houses and other protected environments designed for improving agricultural production. 61 LECTURE NO – 17 COMPOSITION AND STRUCTURE OF THE ATMOSPHERE – DEFINITION OF WEATHER AND CLIMATE – ASPECTS INVOLVED IN WEATHER AND CLIMATE Composition of the atmosphere There is no definite upper layer to the atmosphere. The decrease of air (density) with altitude (height) is so rapid (Figure 1) that half of the atmosphere lies within 3.5 miles (5.5 kms) from the surface and nearly 3/4th of the atmosphere lies upto 7 miles (11 km). The atmosphere is a mixture of many gases. In addition, it contains large quantities of solid and liquid particles collectively called "aerosols". The lower part of the atmosphere contains water vapour from 0.02 to 4 per cent by volume. Nitrogen and oxygen make up approximately to 99 per cent and the remaining 1 per cent by other gases (Table 1). Innumerable dust particles are also present in the lower layers of the atmosphere. They are microscopic and play an important role in absorption and scattering of insolation. Table: 17.1. Principal gases comprising dry air in the lower atmosphere S. No. Constituent Per cent by volume Per cent by weight 1 Nitrogen 78.08 75.51 2 Oxygen 20.94 23.15 3 Argon 0.93 1.28 4 Carbon-dioxide 0.03 0.046 Physical structure of the atmosphere On the basis of vertical temperature variation, the atmosphere is divided into different spheres or layers as detailed below: I Troposphere 1. The word “Tropo” means mixing or turbulence and “Sphere” means region. 2. The average height of this lower most layer of the atmosphere is about 14 kilometers above the mean sea level; at the equator it is 16 kilometers; and 7- 8 kilometers at the poles. 3. Under normal conditions the height of the troposphere changes from place to place and season to season 62 4. Various types of clouds, thunderstorms, cyclones and anti cyclones occur in this sphere because of the concentration of almost all the water vapour and aerosols in it. So, this layer is called as “Seat of weather phenomena”. 5. The wind velocities increase with height and attain the maximum at the top of this layer. 6. Another striking feature of troposphere is that there is a decrease of temperature with increasing elevation at a mean lapse rate of about 6.5oC per kilometer or 3.6oF per 1,000 feet. 7. Most of the radiation received from the sun is absorbed by the earth's surface. So the troposphere is heated from below. 8. In this layer, about 75 per cent of total gases and most of the moisture and dust particles present. 9. At the top of the troposphere there is a shallow layer separating it from stratosphere which is known as “Tropopause”. 10. The tropopause layer is thin and its height changes according to the latitudes and infact this is a transitional zone and distinctly characterised by no major movement of air. II Stratosphere 1. This layer exists above the tropopause (around 20 km onwards) and extends to altitudes of about 50-55 kilometers. 2. This layer is called as "Seat of photochemical reactions". 3. In any particular locality, the temperature remains practically constant at around 20 kilometers and is characterised as Isothermal because the air is thin, clear, cold and dry. 4. The temperature of this layer increases with height and also depends upon troposphere because troposphere is higher at equator than at poles. 5. In the upper parts of the stratosphere the temperatures are almost as higher as those near the earth's surface, which is due to the fact that the ultra violet radiation from the sun is absorbed by ozone in this region. 6. Less convection takes place in the stratosphere because it is warm at the top and cold at the bottom. 7. There is also persistence of circulation patterns and high wind speeds. 8. The upper boundary of the stratosphere is called stratopause and above this level there is a steep rise in temperature. III Mesosphere / Ozonosphere 1. There is a maximum concentration of ozone between 30 and 60 km above the surface of the earth and this layer is known as ozonosphere. 2. A property of ozone is that it absorbs ultra violet rays. Had there been no layer of ozone in the atmosphere, the ultra violet rays would have reached the surface of the earth and no life on it. 65 ♦ The daily or short term variations of different conditions of lower air in terms of temperature, pressure, wind, rainfall, etc”. ♦ The aspects involved in weather include small areas and duration, expressed in numerical values etc. The different weather elements are solar radiation, temperature, pressure, wind, humidity, rainfall, evaporation etc. Weather is highly variable. It changes constantly sometimes from hour to hour and at other times from day to day. Example: The air temperature of Rajendranagar on 20-01-2000 at 2.30 p.m. is 32oC. Climate It is defined as ♦ “The generalised weather or summation of weather conditions over a given region during comparatively longer period”. ♦ “The sum of all statistical information of weather in a particular area during a specified interval of time usually a season or year or even a decade”. The aspects involved are larger areas like a zone, a state; a country is described by normals etc. Example: The climatic elements are latitude, longitude, altitude etc. In Andhra Pradesh the winter temperatures range from 15 to 29oC. Table 17.1 Differences between Weather and Climate. S. No. Weather Climate 1 A typical physical condition of the atmosphere Generalised condition of the atmosphere which represents and describes the characteristics of a region 2 Changes from place to place even in a small locality Different in different large regions 3 Changes according to time (every moment) Change requires longer (years) time 4 Similar numerical values of weather of different places usually have same weather Similar numerical values of climate of different places usually have different climates 5 Crop growth, development and yield are decided by weather in a given season Selection of crops suitable for a place is decided based on climate of the region 6 Under aberrant weather conditions planners can adopt a short-term contingent planning Helps in long-term agricultural planning 66 LECTURE NO – 18 SOLAR RADIATION - DEFINITION, INTRODUCTION OF ELECTROMAGNETIC SPECTRUM AND FUNCTIONS OF LIGHT, SOLAR CONSTANT, NET RADIATION, BLACKBODY RADIATION, EMISSIVITY, ABSORPTIVITY, REFLECTIVITY, TRANSMISSIVITY, AND ALBEDO Introduction Solar radiation is the primary source of energy on earth, and life depends on it. Solar radiation is defined as “The flux of radiant energy from the sun”. All matter at a temperature above the absolute zero, imparts energy to the surrounding space. This energy is transformed by green plants in the process of photosynthesis into the potential energy of organic material. In inorganic bodies the rays absorbed are used in heating. The variations of the total radiation flux from one site to another on the surface of the earth are enormous and the distribution of plants and animals responds to this variation. Solar radiation definition Heat energy is transmitted by three processes. 1 Radiation ♦ This is the process of transmission of energy from one body to another without the aid of a material medium (solid, liquid, or gas). Example: The energy transmission through space from the sun to the earth. 2 Conduction ♦ This is the process of heat transfer through matter without the actual movement of molecules of the substances or matter. Heat flows from the warmer to cooler part of the body so that the temperature between them are equalised. Example: The energy transmission through an iron rod which is made warmer at one end. 3 Convection ♦ This is the process of transmission of heat through actual movement of molecules of the medium. This is the predominant form of transmission of energy on the earth as all the weather related processes involve this process. Example: Boiling of water in a beaker Of the above three processes of transmission of energy convection is the predominant form of transmission of energy on the earth. All the weather related processes involve this process. 67 Fig: 18.1 CONDUCTION, CONVECTION AND RADIATION Fig:18.2 SOLAR SPECTRUM 70 Solar Radiation Reflected by Reflected Reflected from atmosphere by clouds _ earth's surface 6% 20% 4% 64% 6% Radiated to space from clouds and atmosphere Absorbed by atmosphere 16% Radiated directly to space from earth Fig:18.3 Solar Radiation 71 Functions of light: The functions of light are: 1. All the plant parts are directly or indirectly influenced by light 2. Light of correct intensity, quality and duration is essential to normal plant development 3. Poor light availability causes abnormalities and disorders in plants 4. Light is indispensable to photosynthesis 5. Light governs the distribution of photosynthates among different organs of plants 6. Effects tiller production 7. Effects stability, strength and length of culms 8. Effects dry matter production 9. Effects the size of the leaves 10. Effects the root development 11. Effects the flowering and fruiting 12. Effects the dormancy of the seed Solar constant: It is the energy falling in one minute on a surface of 1 cm2 at the outer boundary layer of the atmosphere, held normal to the sunlight at the mean distance of the earth from the sun. The units are cal/cm2/min. "cal/cm2 “is also known as "Lan- gley". The estimated value of this constant is from 1.94 to 2.0 largely/min. The average value is 2 LY/mn. It depends on: 1. Output of solar radiation. 2. Distance between the earth and the sun. 3. Transparency of the atmosphere. 4. Duration of the sunlight period 5. The angle at which the sun's rays strike the earth. Net radiation The difference between the incoming radiation from the sun and the out going radiation from the earth is known as net radiation. The net radiation values become -ve after late evening hours to early morning hours. It is a conservative term and plays an importance role in the energy processes of the crops. Black body: It is an ideal hypothetical body which absorbs all the electromagnetic radiation falling on it. It neither reflects nor transmits any radiation striking it. However, when heated it emits all the possible wavelengths of solar radiation and becomes a perfect radiator. So, an ideal black body is a perfect absorber and a perfect radiator. 72 Black body radiation: The radiation radiated by an ideal black body is known as black body radiation. Emittance: It is the ratio of the emitted radiation of a given surface at a specified wavelength to the emittance of an ideal black body at the same wavelength and temperature. For other than a black body the value of emittance is always less than one and for black body the emittance value is one. Absorptivity: For an object this is the ratio of the electromagnetic radiant power absorbed to the total amount incident upon the same object. Like emissivity the values are less than one for other than a black body and one for a black body. Reflectivity: The ratio of the monochromatic beam of electromagnetic radiation reflected by a body to that incident upon it. The units of expression are by %. Transmissivity: This is the ratio of transmitted to the incident radiation on a surface preferably a crop canopy. Albedo: It is defined as the ratio between reflected radiation to the incident radiation on a crop field, snow, leaves etc. For white bodies the albedo values are high. For fresh snow cover the albedo values range between 75 and 95; for cropped fields - it is 12-13; dark cultivated soil 7-10; human skin 15-25, etc. Albedo determines how much of the heat that reaches the ground in the form of radiation will remain available for use. 75 LECTURE NO – 20 AIR TEMPERATURE – INTRODUCTION -TEMPERATURE AND HEAT DEFINITIONS – ISOTHERMS - HORIZONTAL AND VERTICAL TEMPERATURE VARIATIONS IN THE ATMOSPHERE - CARDINAL TEMPERATURES - IMPORTANCE OF AIT TEMPERATURE TEMPERATURE AND HEAT DEFINITIONS: Temperature is defined as “The measure of speed per molecule of all the molecules of a body” where as heat is “The energy arising from random motion of all the molecules of a body”. The temperature of a body is the condition which determines its ability to transfer heat to other bodies or to receive heat from them. In a system of two bodies the one which looses heat to the other is said to be at a higher temperature. Heat measures total molecular energy. Temperature measures average energy of individual molecules. Temperature is that characteristic of a body which determines the direction of heat flow by conduction. AIR TEMPERATURE Temperature Distribution 1. Each day the earth receives energy in the form of incoming solar radiation from the sun. 2. This shortwave solar radiation ranges mostly from ultra-violet (0.2 µm wavelength) to the near infrared (3.0 microns wavelength), but reaches its maximum at around 0.5 microns wavelength (Blue-green visible light). 3. This insolation is absorbed by the earth’s surface and is converted to heat (long wave radiation) 4. The earth’s (terrestrial) longwave radiation reaches its peak intensity at 10 microns wavelength (thermal infrared) and is responsible for heating the lower atmosphere. Horizontal temperature distribution Sun rays make different angles at the same place at different times. Also different angles at the same time at different places as the axis of the earth makes an angle of 23-50 with the vertical. Due to the variation in angle of sums rays distribution of solar heat on earth decreases both ways from equator to polar. This is known as horizontal distribution of air temperature. On maps, the horizontal distribution of temperature is shown by isotherms. The isotherms are imaginary lines drawn the connecting points that have equal temperature. 76 Fig: 20.1 TEMPERATURE AT DIFFERENT PARTS OF GLOBE. Fig: 20.2 TEMPERATURE CHANGES WITH ALTITUDE 77 Factors influencing horizontal distribution of temperature: 1. Latitude The effectiveness of insolation in heating the earth’s surface is largely determined by the latitude. So, there is a general decrease in temperatures from the equator to poles, which is a classical example of horizontal temperature distribution. 2. Ocean currents Transport of ocean water in the form of currents carries heat from one part of the earth to another which results in horizontal distribution of sea-surface temperature. 3. Mountain barrier: Mountain ranges tend to guide the movement of cold air masses resulting in horizontal temperature variation. Ex: Himalayas protect India from polar air. 4. Topography and relief In the northern hemisphere north facing slopes generally receive less insolation than south facing slopes and temperatures are normally lower. Vertical distribution of temperature: The decrease of air temperature with altitude is known as vertical temperature distribution. Ex: Permanent snow caps in high mountains. Vertical temperature distribution The vertical distribution of temperature is due to adiabatic lapse rate 1. An adiabatic process is one in which the system being considered does not exchange heat with its environment. 2. The most common atmospheric adiabatic phenomena are those involving the change of air temperature due to change of pressure. 3. If an air mass has its pressure decreased, it will expand and do mechanical work on the surrounding air. 4. If no heat is taken from the surroundings, the energy required to do work is taken from the heat energy of the air mass, resulting in a temperature decrease. 5. When pressure is increased, the work done in the air mass appears as heat, causing its temperature to rise. 6. The rates of adiabatic heating and cooling in the atmosphere are described as lapse rates and are expressed as the change of temperature with height. 7. The adiabatic lapse rate for dry air is very nearly 1oC per 100 m. 8. If condensation occurs in the air parcel, latent heat is released, thereby modifying the rate of temperature change. 9. This is known as wet adiabatic lapse rate 80 LECTURE - 21 LOW AIR TEMPERATURE AND PLANT INJURY - HIGH AIR EMPERATURE AND PLA NT INJURY – SOIL TEMPERATURE - FACTORS AEEECTING SOIL TEMPERATURE Air temperature and plant injury Low air temperature and plant injury: On exposure of crop plants to low temperature the following effects are observed. The primary effect of low air temperature below their optimum temperature is the reduction of rates of growth and metabolic processes. 1. Suffocation a Small plants may suffer from deficient oxygen when covered with densely packed snow. b Certain toxic substances accumulate in roots and crowns because of low diffusion of carbon dioxide 2. Physiological drought a In middle latitudes drought occurs under cool temperature conditions. This is due to excessive transpiration and absence of absorption of moisture from the soil, when the soil is in extremely low temperature conditions. b The internal water content of crop plants is depleted which may result in death of leaves. 3. Heaving a The injury to a plant is caused by lifting upward from the normal position causing the root to stretch or break at a time when the plant is growing. b Sometimes the roots are pushed completely above the soil surface. c It is difficult for the roots to become firmly established again and the plants may die because of this mechanical damage and desiccation. 4. Chilling a Due to this injury some crop plants are killed and others recover under favourable conditions later on. b This injury is common in temperate climates where delayed growth and sterility are common symptoms. c Moderate wind speeds when the air temperature ranges from 0 to 10oC, tends to cause very rapid fall in the activity of metabolic processes, especially respiration in crop plants. Which is known as “chilling injury”. This results in severe damage and death within a few hours or days. d Chilling in the affected plants causes a phase change (“liquid” to “solid”) in membrane lipids resulting in inactivation of membrane bound enzymes. e Sometimes chilling results yellowing of plants. 81 5. Freezing 1 Freezing damage is caused by the formation of ice crystals in the intracellular spaces and extracellular spaces. 2 Ice within the cells cause injury by mechanical damage and plant parts or entire plant may be killed or damaged. 3 If extracellular ice persists, the gradient of water vapour pressure between the apoplast and the cells causes water to migrate out of the cells and into the apoplast, where it freezes, thereby increasing the amount of ice, in the plant tissue. 4 This results not only in mechanical damage to the tissue, but also brings about dehydration of cell contents and lead to death of the cell. II High air temperature and plant injury 1 High air temperature results in the desiccation of the crop plants also. 2 The injury caused because of short period fluctuation (within a day highest in noon and lowest at early morning) in air temperature is known as sunclad. 3 The scorching of stem near the soil surface known as stem girdle is another injury at high air temperatures. 4 Plant tissues escape from high heat by emission of long wave radiation, convection of heat, and transpiration. 5 However, transpiration is the most effective process in many natural situations. 6 High plant temperatures (> 40oC) are almost invariably due to the cessation of transpirational cooling, caused by stomatal closure. 7 Exposure of crop plants to temperatures over 45oC for just 30 minutes can cause severe damage to the leaves of plants. 8 The effect of high temperature are the disruption of cell metabolism (possibly by protein denaturation), production of toxic substances, and damage to cellular membranes. Cardinal temperatures There are three points of temperature which influence the growth of crop Factors affecting soil temperature Heat at ground surface is propagated downward in the form of waves. The amplitude decreases with depth Figures ___ and ___ show different factors that effects soil temperature. Both meteorological and soil factors contribute in bringing about changes of soil temperature. 82 I Meteorological factors 1. Solar radiation a The amount of solar radiation available at any given location and point of time is directly proportional to soil temperature b Even though a part of total net radiation available is utilised in evapotranspiration and heating the air by reradiation (latent heat and sensible heat fluxes) a relatively substantial amount of solar radiation is utilized in heating up of soil (ground heat flux) depending up on nature of surface. c Radiation from the sky contributes a large amount of heat to the soil in areas where the sun’s rays have to penetrate the earth’s atmosphere very obliquely. 2. Wind Air convection or wind is necessary to heat up the soil by conduction from the atmosphere. Example: The mountain and valley winds influence the soil temperature. 3. Evaporation and condensation a The greater the rate of evaporation the more the soil is cooled. This is the reason for coolness of moist. Soil in windy conditions. b On the other hand whenever water vapour from the atmosphere or from other soil depths condenses in the soil it heats up noticeable. Freezing of water generates heat. 4. Rain fall (precipitation) Depending on its temperature precipitation can either cool or warm the soil. II. Soil factors 1. Aspect and slope a In the middle and high latitudes of the northern hemisphere the southern slopes receive more insolation per unit area than the northern exposure (Fig. ___). b The southwest slope are usually warmer than the south east slope. The reason is that the direct beam of sunshine on the southeast slope occurs shortly after prolonged cooling at night, but the evaporation of dew in the morning also requires energy. 2. Soil texture a Because of lower heat capacity, poor thermal conductivity sandy soils warmup more rapidly than clay soils. The energy received by it is concentrated mainly in a thin layer resulting in extraordinary rise in temperature. b Radiational cooling at night is greater in light soils than in heavy soils. In the top layer, sand has the greatest temperature range, followed by loam and clay. c The decrease of range with depth is more rapid in light soils than heavy soils CYCLONE ANTICYCLONE LOW PRESSURE AREA HIGH PRESSURE AREA et RO ees EE Pr eee a ISOTHERMS 80 Lorn amene rr Fig:22.1 Cyclone and Anticyclone 85 86 A single severe cyclone can perish hundreds of human lives, animal populations, and submerge thousands of hectares of standing crop. ♦ The diameter of a cyclone ranges from a few hundreds to 2000 kilometers. ♦ Floods are the results of the cyclones. ♦ The devastation could be attributed to the absence of – Timely warning – Lack of awareness among the people – Inadequate preparedness – Poor response and participation. ♦ Cyclones are recurring feature in India. 2. High pressure systems or anticyclones When isobars are circular, elliptical in shape and the pressure is highest at the centre such a pressure system is called “High” or “Anticyclone”. When the isobars are elliptical rather than circular the system is called as a “Ridge” or “Wedge”. Table: 22.1. Differences between cyclones and anticyclones S. No. Cyclones Anticyclones 1. Lowest pressure at the centre and it increases towards the outer rim gradually. Highest pressure at the centre and it decreases towards the outer rim gradually. 2. Relative humidity increases towards centre and bring cloudy weather. Relative humidity decreases and clouds are dissipated giving fair weather. 3. Variety of clouds lies at different heights. Little clouds with cool dry air are usually associated. 4. Highest rainfall occurs at the front side. Rainfall is almost negligible. 5. Wind velocity increases from outer rim to the centre. Wind velocities ask much lesser than cyclones (Wind spirally rushes outward from the centre to periphere). 6. Move in anticlock wise in northern hemisphere and clock wise in southern hemisphere Move in clock wise in northern hemisphere and anti clock wise in southern hemisphere. WIND Air in horizontal motion is known as “Wind”. Winds are named by the direction they come from. Windward refers to the direction a wind comes from and leeward is the direction towards which it flows. The wind which flows more frequently from one direction than any other is called as “Prevailing wind”. 87 Importance of wind crop plants 1 Transports heat in either sensible or latent form, from lower to higher latitudes, 2 Provides the moisture (to the land masses) which is necessary for precipitation 3 Moderate turbulence promotes the consumption of carbon – dioxide by photosynthesis. 4 Wind prevents frost by disrupting a temperature inversion 5 Wind dispersal of pollen and seeds is natural and necessary for certain agricultural crops, natural vegetation, etc. 6 Action of wind on soil Wind causes soil erosion in two ways a Strong wind flows loose and course soil particles (sand) and dust for long distances. In some areas all the soil is blown by this way, and no cultivation is possible in such areas. b In dry countries and sea shores, strong wind is seen to eat up a cliff or a hard rock. When strong wind armed with millions of small particles of sand flows against a cliff or a hard rock, it gradually eats it up. The action is strongest near the ground so that the rock is undercut and eventually falls over. Mountain and valley winds 1 The daily up-valley winds and nightly down-valley winds are commonly found in mountainous regions. 2 During day time the slopes of mountains heat up rapidly because of intensive insolation. 3 But, the free atmosphere at the same elevation over the low lands is not heated to the same extent. 4 This results in warm air moving up along the slope. This up slope breeze is called as the “Valley breeze” or “Valley winds”. 5 However, at night the temperature difference between mountain slopes and free atmosphere at the same elevation is reversed. 6 Nocturnal radiation brings about a more rapid cooling of mountain slopes as a result of which the cool air drains into the valley below. 7 This, down-slope wind is called the “Mountain breeze” or “Mountain wind”. 90 LECTURE NO – 23 ATMOSPHERIC HUMIDITY AND ITS EXPRESSION – SATURATION - EFFECTS OF HUMIDITY ON CROPS HUMIDITY Expression or Measures of humidity A. Mass and volume based measures Specific humidity It is defined as the ratio of the mass of water vapour in a sample of moist air to the total mass of the sample. It is expressed as kg of water vapour in a kg of moist air. Absolute humidity It is the ratio of the mass of water vapour to the volume of moist air in which it is contained. Absolute humidity is expressed as kg m-1. Mixing ratio It is the ratio of the mass of water vapour contained in a simple of moist air to the mass of dry air. It is expressed as kg water vapour per kg dry air. B. Saturation based measure Relative humidity It is expressed as the ratio of actual vapour pressure to the saturated pressure expressed in terms of percentage. It is most common measure of atmospheric humidity. Vapour pressure deficit It is another measure of moisture in the atmosphere. It is the difference between the saturated vapour pressure and actual vapour pressure. Dew point It is defined as the temperature to which a given parcel of air must be cooled at constant pressure and constant water vapour content in order to become saturationed. 91 Effects of humidity on crops Humidity is an important factor in crop production and it is not an independent factor but closely related to rainfall and temperature. It plays significant role in weather and climate. The dampness of air is called humidity. a. Humidity is the invisible vapour content of the air and is of great importance in determining the vegetation of a region. b. it affects the internal water potential of plants. c. Humidity is a major determinant of potential evapotranspiration. So, it determines the water requirement of crops. d. It influences certain physiological phenomena including transpiration. e. Change in relative humidity can produce various morphological and anatomical changes in the plants. For example, orchids grow abundantly in humid forests as epiphytes depend for their moisture supply on the atmosphere by developing certain morphological and anatomical characteristics that are not found in other plants (hydroscopic aerial roots). f. Xerophytes in desert region where relative humidity is low show certain adaptations to conserve water. g. High relative humidity can prolong the survival of crops under moisture stress. h. Relative humidity plays a significant role in the outbreak of disease and pest epidermics. High humidity promoters the growth of some saprophytic and parasitic fungi and bacteria which cause various plant diseases. i. Very high or very low relative humidity is not conductive for higher yields. 92 LECTURE NO – 24 EVAPORATION AND TRANSPIRATION – DEFINITIONS - FACTORS AFFECTING RATE OF EVAPORATION AND TRANSPIRATION Evaporation The sun is the source of energy that activates the hydrologic cycle i.e. the heat required for evaporation is supplied by the sun. The moisture in the atmosphere is supplied by evaporation. Evaporation is defined as “A physical process in which liquid water is converted into its vapour”. In this process molecules of water having sufficient kinetic energy to overcome the attractive forces tending to hold them within the body of liquid water are projected through the water surfaces. Factors affecting the evaporation Evaporation losses from a fully exposed water surface are essentially the functions of several factors. I Environmental factors 1 Water temperature: With an increase of temperature the kinetic energy, of water molecules increases and surface tension decreases. So, the rate of evaporation increases with a rise in temperature. The maximum amount of water vapour that can exist in any given space is a function of temperature. 2. Wind: The velocity of wind is directly proportional to evaporation from a fully exposed surface and vice versa. The reason is that the dry wind replaces the moist air near the water. The process of evaporation takes place continuously when there is a supply of energy to provide latent heat of evaporation (approximately 540 calories per gram of water evaporated at 100oC). 3 Relative humidity: A mechanism to remove the vapour so that the vapour pressure of the water vapour in the moist layer adjacent to the liquid surface is less than the saturated vapour pressure of the liquid i.e., a vertical gradient of vapour pressure exists above the surface. When the air above water is dry or has low relative humidity, the evaporation will be greater than when air has high relative humidity over the water. 4 Pressure: The evaporation is more at low pressure and vice versa. 95 2 Leaf characteristics: In some plants like cacti and other desert plants leaves are altogether absent and their function taken up by the stem itself. In case of Pines, Firs etc., the leaf size is very much reduced. In such cases reduction in leaf area brings about reduction in transpiration. Some graminaceae family plants (maize), flower plants, etc., roll up or turn the edges of their leaves when exposed to bright sun and fast breeze. This causes reduction in the transpiration. 3 Availability of water to the plant: If there is little water in the soil, the tendency for dehydration of leaf causes stomatal closure and a consequent fall in transpiration. This situation occurs during a) periods of drought b) when the soil is frozen and c) at a temperature so low that water is not absorbed by roots. 96 LECTURE-25 RAINFALL - IMPORTANCE OF RAINFALL (WATER) ON CROPS -TYPES OF RAINFALL - MONSOON DEFINITION - ORIGIN AND DISTRIBUTION OF SOUTHWEST MOONSOON Importance of rainfall (water) on crop plants One centimetre of rain over an area of one hectare or 100 m3 (100,000 litres) contains 4,339 grams of oxygen at 20oC. This is equivalent to 3,000 litres of pure oxygen at atmospheric pressure. Consequently, a rain usually has a much more invigorating effect on a crop than does irrigation. Rain water has extraordinary qualities. 1 Water has high solvent power and this plays an important role in crop plants as the plants get their nourishment from soil only in solution form. 2 Water plays an important role in life processes of crop plants (in the exchange of gases). 3 The heat capacity of water is high and its high thermal stability helps in regulation of the temperature of crop plants. 4 Water has highest heat conduction capacity and due to this the heat produced by the activity of a cell is conducted immediately by water and distributed evenly to all plant parts. 5 The viscosity of water is higher than that of many solvents and this property helps in protecting the crop plants and trees against mechanical disturbances. 6 Water is driest at 4oC. The freezing point of fresh water being 0oC and that of sea water about – 2.5oC, the ice can float on the surface and plant life in deeper parts of sea is made possible. 7 The transparency of water facilitates the passage of light to great depths and this helps for the survival of aquatic plants. 8 The high surface tension that water has helps in movement of water into and through the plant parts. 9 Rainfall influences the distribution of crop plants in particular and vegetation in general, as the nature of vegetation of a particular place depends on the amount of rainfall (the vegetation of a desert where rainfall is less differs a lot from the vegetation of a rainforest). 97 Types of rainfall There are mainly 3 types of rainfall which are as follows: 1. Convectional rains 1 The air near the ground becomes hot and light due to heating. Then it starts upward movement. This process is known as convection (This differs slightly from `Convection' defined in Chapter (2). 2 As the air moves upward it cools at about 10oC per kelometer i.e., at dry adiabatic lapse rate. 3 As it becomes saturated, relative humidity reaches to 100 per cent and dew point is reached where the condensation begins. This level (height) is known as condensation level. 4 Above this level, air cools at about 4oC per kilometre slightly less than i.e., saturated adiabatic lapse rate. First, cloud is formed. 5 Then, the further condensation results into precipitation. These rains are known as convectional rains and mostly occurs in the tropics. 2. Orographic rains 1 When moist air coming from the sea or ocean strikes mountain it can not move horizontally. It has to over come the mountations. 2 When this air rises upward, cools down, cloud is formed and condensation starts giving precipitation. 3 These rains are known as orographic rains. 4 These are also known as `relief rains" as the rains also occurs when the air from sea or ocean strike or pass over relief barriers. 5 Due to these processes rains with high intensity are possible on the windward side of the mountain. 3. Cyclonic and frontal rains 1 The rains received from cyclones are known as `cyclonic rains' (Chapter 6). 2 When two opposing air currents with different temperatures meet, vertical lifting takes place. 3 This convection gives rise to condensation and precipitation which is known as frontal precipitation. The size of the rain drop reaching the ground depends upon the following points.