Agronomy: Principles and Practices for Soil, Water, and Crop Management, Schemes and Mind Maps of Vocational education

Download Agronomy: Principles and Practices for Soil, Water, and Crop Management and more Schemes and Mind Maps Vocational education in PDF only on Docsity! UNIVERSITY OF AGRICULTURAL SCIENCES, DHARWAD INTRODUCTION TO AGRONOMY (AGR - 104) Prepared by Dr. Smt. Ganajaxi Math Dr. Sudha T. Dr. Rajkumara, S. 2019-20 DEPARTMENT OF AGONOMY COLLEGE OF AGRICULTURE, DHARWAD Theory Agronomy and its scope, seeds and sowing, tillage and tilth, crop density and geometry, crop nutrition, manures and fertilizers, nutrient use efficiency, water resources, crop water requirement, WUE, irrigation scheduling, criteria and methods, quality of irrigation water, water logging, drainage, weeds- importance, classification, crop weed competition, concepts of weed management principles and methods, herbicides. Growth and development of crops, factors affecting growth and development, crops and cropping systems, crop rotation and its principles, crop management technologies, harvesting and threshing of crops. Practical Identification of crops, seeds, fertilizers, herbicides and tillage implements. Effect of sowing depth on germination and seedling vigour. Identification of weeds in crops, methods of herbicide and fertilizer application, study of yield contributing characters and yield estimation, numerical exercises on fertilizer requirement, plant population, herbicides and water requirement. Use of tillage implements – reversible plough, one way plough, harrow, leveller, seed drill, methods of irrigation Ref: Gopal Chandra De, 1999, Fundamentals of Agronomy, Oxford and IBH Publishing Company Singh, S. S. 1988, Crop management under irrigated and rainfed conditions. Kalyani Publishers Reddi and Reddy, 1995, Efficient use of irrigation water. Kalyani Publishers the field and accept them finally and also judge the reactions of farming community. He is a key person with working knowledge of all agricultural disciplines and coordinator of different subject matter specialists. The fundamental principles of agronomy are; Planning, programming and executing measures for maximum utilization of land, labour, capital, sunshine, rain water, temperature, humidity, transport and marketing facilities Choice of crops, varieties adaptable to the particular agroclimate, land situation, soil fertility, season and method of cultivation Proper field management – tillage, bunds, irrigation channels, drainage lines, checking soil and water erosion, levelling etc., Adoption of multiple cropping/intercropping/relay cropping according to different situations Timely application and management of manures, fertilizers, biofertilizers, organics, crop residues, weed and water management Adoption of need based plant protection measures, harvesting and processing Lecture -2 Seeds and sowing Seed: Seed may be defined as a fertilized ovule constituting of intact embryo, staved food and seed coat which in viable and has got a capacity to germinate. When water is plenty, the seeds imbibe water and this is imbibition. The water activates special proteins called enzymes and seed growth starts. In the beginning of seed germination, first the seed grows in to a root to access soil moisture present in the soil. Later shoot appears above the ground. Seed material: 1. Seeds (grains used for sowing) 2. Veg propagules (stem cutling’s rooted slips, tubers, rhizomes, etc) Stem cutlings – sugarcane, rose Rooted slips – forage crops. (Fodder crops) Tubers – potato Rhizomes – turmeric Quality of seeds is determined by following factors 1. Purity: Free from rogues (off types), other crop seeds, weed seeds and inert material. 2. Fully matured and well developed. free from storage pests and seed borne diseases Ex. Red rot in sugarcane, Tikka leaf spot in groundnut. 3. Free from dormancy (seen in groundnut, rice, sunflower). Viable (soybean looses viability quickly). 4. High percentage of germination (98-99%) (germination percentage in many grasses is 20-25%). Prerequisites for sowing: 1. Well prepared soil wood tilth 2. Optimum soil moisture at sowing depth 3. Manures, fertilizers and seeds Sowing: Placing of seed in soil at proper depth to obtain better germination and uniform plant stand of the crop. METHODS OF SOWING ______________ǀ______________________ ǀ ǀ Direct seeding Transplanting ___________ǀ____________ Broad casting Line sowing ________________ǀ____________________ ǀ ǀ Drilling Dibbling Time of sowing: 1. Sowing very early in the season may not be advantageous. Ex: sowing rainfed ground nut early may result in failure of crop if there is a prolonged dry spell from the 2nd week of June to 2nd week of July. 2. Delayed sowing invariably reduces yields a. Rainfed sorghum yields are reduced due to delay in sowing beyond June season – sorghum sown late is subjected to severe attack of sorghum shoot borer. b. 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. a. Optimum time of sowing for Kharif crop – June or July b. Optimum time for Rabi crop - last week of October to first week of November c. 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. 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 1 cm. Bold seeded crops like castor, groundnut, cotton, and maize etc. 6-7 cm. 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 with 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. Inter cultivation: 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 Inter cultivation starts from very early stage of crop i.e., two to three weeks from sowing. Short duration crops require two-three inter cultivation while long duration crop require 3-4 weeks. After cultivation: It includes inter cultivation 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, maize 4. Cropping in banana 5. De suckering operation banana 6. Wrapping and propping in sugarcane 7. Nipping in castor, chickpea, pigeonpea 8. Topping, trimming and de suckering in tobacco basal leaves are removed 9. Defoliation in cotton 10. Hand pollination in sunflower. Fertilizer app in irrigation also comes under after cultivation. Lecture 4 Planting Geometry – Competition – Types of Competition Competition is the struggle between individuals with in a population for available resources, when the level of resources is below the combined need of the members of the population. Crop plants are not grown in isolation but in closely spaced populations. In the early phase of growth, individual plants are small and widely spaced and do not interfere with each other. At some point, as the plants grow, they start to interfere with their neighbours and competition begins. Two plants, no matter how close, do not compete with each other so long as the growth resources are in excess of the needs of both. When the immediate supply of a single necessary factor falls below the combined demand of the two plants, competition begins. Types of Competition 1. Competition for nutrients: Nutrient uptake increase with increase plant population. Higher population under low fertility conditions leads to development of nutrient deficiency symptoms because of competition. 2. Competition for light: Competition for light may occur whenever one plant casts a shadow on another or within a plant when one leaf shades another leaf. In early plant growth stages, there will be little mutual shading and even at relatively low light intensities the plant will be able to photosynthesize with full efficiency. As the plants develop, mutual shading increase and light becomes a limiting factor. 3. Competition for water: The success of any plant in community for water depends on the rate and competitiveness with which it can make use of the soil water supply. 4. Intra-specific and inter-specific competition: In populations of similar genotypes, in the absence of weeds, the competition is intra-specific (with in species), where different species of crops are growth, in mixtures and where weeds present, the competition is inter-specific (between species). 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. Ex. 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 congenial for growth during pre-anthesis, it is four lakh plants/ha. Plant Geometry The arrangement of the plants in different rows and columns in an area to utilize the natural resources efficiently is called crop geometry. It is otherwise area occupied by a single plant Ex.. Rice – 20 cm x 15 cm. This is very essential to utilize the resources like light, water, nutrient and space. Different geometries are available for crop production Different crop geometries 1) Random plant geometry Random plant geometry results due to broadcasting method of sowing and no equal space is maintained. Resources are either under utilized or over exploited. 2) Square plant geometry The plants are sown at equal distances on either side. Mostly perennial crops, tree crops follow square method of cultivation. Ex. Coconut – 7.5 x 7.5 m; banana – 1.8 x 1.8 m. But, due to scientific invention, the square geometry concept is expanded to close spaced field crops like rice too. Advantages Fig: Phosphorus in soil Soil fertility Soil productivity 1. It is considered as an index of available nutrients to plants 1. It is a broader term used to indicate yields of crops. 2. It is one of the factors for crop production. The other factors are water supply, slope of the land, depth of water table etc. 2. It is the interaction of all the factors that determine the magnitude of yields. 3. It can be analysed in the laboratory 3. It can be assessed in the field under particular climatic conditions. 4. It is the potential status of the soil. 4. It is the resultant of various factors soil factors influencing soil management to produce crops. Denitrification: NO3 NO2 NO2 N2 Volatilization: NH4 + H2O NH3 + 2 H2O Soil fertility can be maintained by: a) Cultural practices fallowing crop rotation mixed cropping b) By addition of materials 1. Organic manures – (bulky and concentrated) 2. Inorganic fertilizers 3. Bio-fertilizers – rhizobium, azolla, azatobactor, BGA. 4. Soil amendments – lime, gypsum, paddy husk, groundnut shells etc. 5. Weedicides or fungicides – copper fungicides – add Cu Triazines – add N. 6. Green manures or green leaf manuring 7. Crop residues (stubbles, etc.) 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. Essential nutrients The term mineral nutrient is generally used to refer to an inorganic ion obtained from the soil and required for plant growth. The process of absorption, translocation and assimilation of nutrients by the plants is known as mineral nutrition. Plants need 16 elements for their growth and completion of life cycle. They are: carbon, hydrogen, oxygen, nitrogen, phosphorus, potassium, calcium, magnesium, sulphur, iron, manganese, zinc, copper, boron, molybdenum and chlorine. In addition, four more elements viz., sodium, cobalt, vanadium and silicon are absorbed by some plants for special purposes. All these elements are not required for all plants, but all have been found essential for one plant or the other. Among these, all carbon atoms and most of the oxygen atoms are derived from carbon dioxide which is assimilated principally in photosynthesis. More specifically, approximately one-thirds of oxygen atoms in organic material in higher plants are derived from soil water and two-thirds from carbon dioxide of the atmosphere. The chemical basis for this conclusion is the reaction occurring during photosynthesis, wherein one molecule each of carbon dioxide (CO2) and water (H2O) are combined in the presence of enzymes. The elements C, H, O are not minerals. The rest of the elements are absorbed from the soil and these are called mineral elements since they are derived from minerals. These mineral elements are mainly absorbed in ionic form and to some extent in non-ionic form as shown in table 1. Criteria of Essentiality Plant analysis using modern techniques reveals that plant body contains about 30 elements and in some cases as many as 60 elements. The presence of several elements in plant does not mean that all these are essential for plants. Arnon and Stout (1939) proposed criteria of essentiality which was refined by Armon (1954). 1. An element is considered as essential, when plants cannot complete vegetative or reproductive stage of life cycle due to its deficiency; 2. This deficiency can be corrected or prevented only by supplying this element; and 3. The element is directly involved in the metabolism of the plant. Forms of mineral elements absorbed by plants Mineral element Ionic form Non-ionic form Nitrogen (N) NH4 +, NO3- CO (NH2)2 Phosphorus (P) H2PO4-, HPO4 2 Nucleic acid, phytin Potassium (Kalium-K) K+ Calcium (Ca) Ca2+ Magnesium (Mg) Mg2+ Sulphur (S) SO4 2 SO2 Iron (Fe) Fe2 Fe3 FeSO4 with EDTA Manganese (Mn) Mn2 MnSO4 with EDTA Zinc (Zn) Zn2+ ZnSO4 with EDTA Copper (Cu) Cu2+ CuSO4 with EDTA Boron (B) B4O7 2,H2BO3,HBO3 2 Molybdenum (Mo) M0O4 Chlorine (Cl) Cl EDTA = ethylenediaminetetracetic acid This criteria is considered as too rigid from practical point of view. According to this criteria, sodium is considered as non essential. However, sodium is known to increase yield of several crops such as an essential element. Nicholas (1961) proposed the term ‘functional nutrient’ for any mineral element that functions in plant metabolism whether or not its action is specific. With this Lecture - 6 Manures and Fertilizers and Integrated Nutrient Management Manures Manures may also be called as ‘Organic manure’. Some of the organic wastes or by-products (extracts of animals and birds, litter, crop refuses, and other by- products) either decomposed or treated or fresh are used to enrich soil fertility. These are called manures. Manures may be bulky (nutrient contents are very low per unit area) such as farm yard manures (FYM), and compost or concentrated (containing a higher per cent of nutrients) such as oilcakes, meals of blood, meat, bone, fish, horns and hooves. Fertilizers Broadly, a fertilizer may be defined as any substance (chemical, organic and microbial) that is added to the soil supply element (s) required for the nutrition of plants (BARC, 2012). In a specific sense, fertilizers are chemicals that occur naturally or are produced in the factory and when added to the soil, supply nutrient elements required for better plant growth. Differences between manures and fertilizer Sl. No Manures Fertilizers 1. Naturally occurring substance. Artificially made. 2. Generally bulky in nature. i.e. concentration of plant nutrient is low. Concentration of plant nutrient is high. 3. Obtaining from organic sources. Obtaining from inorganic sources. 4. Easy to prepare. Preparation is complex. 5. Excess application is not harmful to soil. Excess application may cause harmful effect to soil. 6. Release plant nutrient in available form slowly. Release plant nutrient in available forms quickly. 7. Residual effect is high. Residual effect is low. 9. Improves the physical properties of soil. Does not improve the physical properties of soil, but sometimes it may cause negative effect on soil properties. 10 . Cost of preparation is low. Cost of production is high. 11 They have no definite chemical formula. They have definite chemical formula. List of manures The followings are some important organic manures a. Cowdung b. Farm yard manures c. Compost d. Poultry manures e. Oil cakes f. Blood meal g. Meat meal h. Fish meal i. Green manures etc. j. Vermicompost List of fertilizers Nitrogenous fertilizer: Sodium nitrate, Calcium nitrate, Ammonium chloride, Ammonium sulphate, Anhydrous ammonia, Ammonium nitrate, calcium ammonium nitrate (CAN), Ammonium sulphate nitrate (ASN), Urea, Calcium cyanamide Phosphatic fertilizer: Single super phosphate (SSP), Triple super phosphate (TSP), Ammonium phosphate, Dicalcium phosphate, Basic slag, Rock phosphate. Tricalcium phosphates Potassic fertilizer: Muriate of potash (MOP), Potassium sulphate, Potassium nitrate, Potassium magnesium nitrate Factors Affecting Manures and Fertilizers Use Major factors influencing the selection, quantity, time and method of application of manures and fertilizers are: Soil factors - They most important factors are, soil physical condition (texture), soil fertility and soil reaction. Poor physical condition of the soil leads to poor plant growth due to impeded drainage, restricted aeration and unfavourable soil temperature. In this condition nutrients will not be used efficiency. Optimum soil moisture regime is essential for efficient use of fertilizers by crops. The availability of nutrients is poor in coarse textured soil when compared to fine textured soils. The coarse textured soil needs more frequent application of fertilizers when compared to heavy textured soil. The higher the fertility of soil, the lower is the response to manures and fertilizers. When the organic matter of the soil is higher, the response to fertilizer by crops is more. Soil reaction is important for selection of right type of fertilizers Rock Phosphate is advantageous in acid soils. Crop factors The response of crop to fertilizers varies with the nature of crop and variety of the crop. The fertilizer responsiveness of a plant depends on the cation exchange capacity (CEC) of the roots. The root CEC of dicotyledonous plants is much higher than that of monocotyledonous plants. Plants with higher CEC absorb more of divalent cations (Ca, Mg) whereas plants with low CEC absorb more of monovalent ions (K, Na). The ability of the crop to absorb nutrients from the soil depends upon the size of the root system (root length and spread) and characteristics like root surface and root hair density etc. Large ramifying root system absorbs more nutrients. The association of mycorrhizal fungi with the roots of plants grown under conditions of low soil fertility, increases the ability of plants to absorb nutrients such as P, K, Cu and Zn. Normally N, P and complete fertilizer application reduce the presence and activity of Mycorrhiza. Agronomic factors - Fertilizer responsiveness of crops depends on timely sowing, proper spacing, proper dose, time and method of fertilizer application. (b) Row placement - In widely spaced crops between rows (Example–Sugarcane, maize, tobacco, potato) manures or fertilizers are placed on one or both sides of the row in continuous bands. (c) Circular placement - Application of manures and fertilizers around the hill or the trunk of fruit tree crops in the active root zone. (iii) Pocket placement - Application of fertilizers deep in soil to increase its efficiency Especially for the sugarcane pocket placement is done. Fertilizers are put in 2 to 3 pockets opened around every hill by means of a sharp stick. (iv) Side dressing - It refers to hill and ring placement of manures or fertilizers. It consists of spreading the fertilizer between the rows or around the plants. (v) Pellet application - Nitrogen fertilizers are pelleted like mud ball or urea super granules (USG) and placed deep (10 cm) into the saturated soils (reduced zone) of wet land rice to avoid nitrogen loss from applied fertilizers. Generally placement of fertilizer is done for three reasons. • Efficient use of plant nutrients from plant emergence to maturity. • To avoid the fixation of phosphate in acid soils. • Convenience to the grower. II. Liquid form Foliar application: It refers to spraying of fertilizer solution on the foliage of plants for quick recovery from the deficiency (either N or S). Fertigation: It is the application of fertilizer dissolved in irrigation water in either open or closed system i.e., lined or unlined open ditches and sprinkler or trickle systems respectively. Starter solutions: They are solutions of fertilizers prepared in low concentrations which are used for soaking seeds, dipping roots, spraying on seedlings etc., nutrient deficient areas for early establishment and growth. Direct application to the soil: Liquid fertilizers like anhydrous ammonia are applied directly to the soil with special injecting equipments. Liquid manures such as urine, sewage water and cattle shed washing are directly let into the field. Integrated Nutrient Management (INM) Judicious combination of inorganic, organic and bio-fertilizers which replenishes the soil nutrients removed by the crops is referred as integrated nutrient management system. A. Concept The concept of INM is to integrate the nutrient sources and methods of organic and inorganic nutrient application to maintain soil fertility and productivity i.e., the complementary use of chemical fertilizers, organic manures and bio-fertilizers to solve the problems of nutrient supply, soil productivity and environment. Developing an INM system for a particular crop sequence to a specific location requires a thorough understanding of (i) the effects of previous crop, (ii) contribution of legume in the cropping system, (iii) residual effect of fertilizers, and (iv) direct, residual and cumulative effect of organic manures for supplementing and complementing the use of chemical fertilizers. The main components of the N supply system are the organic manures green manures, crop residues, crop rotation and inter cropping involving legumes and cereals, bio-fertilizers including rhizobium, azotobacter, azospirillum, phosphorus solubilizing micro-organisms like mycorrhizal fungi, azolla, blue green algae and cyanobacteria. All these can serve as an important supplementary source of nutrients along with the chemical fertilizers. Thus, INM is environmentally non- degradable, technically appropriate economically viable and socially acceptable. Balanced nutrition for sustainable crop production The rate of growth of agriculture in its broad coverage of crop production is much below the national growth rate. If the economy of country is to be improved through agriculture, it has to strengthen its programmes in such a manner to better utilize the natural resources along with balanced use of chemical fertilizers and other inputs. For increasing the food production to fulfill the food requirements of the burgeoning population of the country, sustainability of agriculture and environmental safety are the priority issues. To avoid wastage of precious national resources and to minimize the environmental damage, there is need to develop and demonstrate balanced use of chemical fertilizer. This will not only improve the crop production in sustainable way but also economize the crop production. Higher food production needs higher amount of plant nutrients. As no single source is capable of supplying the required amount of nutrients, integrated use of all sources is a must to supply balanced nutrition to plants. What is balanced nutrition? Balanced fertilization does not mean a certain definite proportion of N, P and K or other nutrients to be added in the form of fertilizer, but it has to taken into account the availability of nutrients already present in the soil, crop requirement and other factors like crop removal of nutrients, the economics of fertilizers and profitability, farmers ability to invest, agro-techniques, soil moisture regime, weed control, plant protection, seed rate, sowing time, soil salinity, alkalinity, physical environment, microbiological condition of the soil, available nutrient status of soil, cropping sequence, etc. It is not a state but a dynamic concept. The balanced use of fertilizers should be mainly aimed at: (a) increasing crop yield, (b) increasing crop quality, (c) increasing farm income, (d) correction of inherent soil nutrient deficiencies, (e) maintaining or improving lasting soil fertility, (f) avoiding damage to the environment, and (g) restoring fertility and productivity of the land that has been degraded by wrong and exploitative activities in the past. Balanced use of plant nutrients corrects nutrient deficiency, improves soil fertility, increases nutrient and water use efficiency, enhances crop yields and farmer’s income, improves crop and environmental quality. To reap the benefits of balanced use of plant nutrients, it is important to have good quality seed, adequate moisture and better agronomic practices with greater emphasis on timeliness and precision in farm operations. WATER MOVEMENT IN THE SOIL Water movement in the soil comprises of three phases: infiltration, redistribution and withdrawal. Immediately after application of irrigation or on receipt of rain, water enters the soil. It gradually redistributes into different layers. Water moves from higher potential to lower potential. The movement may be lateral, upwards or downwards or downwards depending on difference in water potential in different parts of the soil. Water moves through unsaturated dry soil as vapour as a result of temperature differences and the movement is from warm to cold areas. Soil air is always saturated with water vapour except in the upper most half to one centimeter layer of soil or under extreme dry conditions. Below a depth of 5-10 cm, the vapour pressure is generally greater than that of the atmosphere. During the day, solar energy is absorbed by the shallow layer of soil which becomes warmer than the atmosphere above and underlying soil layers. As a result, water vapour moves upwards from the surface layers into the atmosphere and downward into cooler layers where it condenses. During night, the opposite movement occurs in the soil. Water vapour moves and condenses near the soil surface. WATER UPTAKE Water is absorbed mainly through roots and hairs. Root system has enormous surface area that is active in water absorption. Roots absorb water both passively and actively. Passive absorption takes place when water is drawn into the roots by negative pressures in the conducting tissue created by the transpiration. Under conditions during which there is a little transpiration, the roots of many plants absorb water by spending energy which is called active absorption. Under normal conditions of transpiration, the contribution of active absorption to the water supply of plants is negligible and it is usually less than 10 per cent of the total absorption. Certain plants are able to absorb moisture from the atmosphere when soil is at permanent wilting point. This is known as aerial absorption or negative transpiration. Direct absorption of water by leaves that are wetted by rain, dew or overhead irrigation can help to resaturate dehydrated leaf tissues. Lecture no-8 Kinds of soil water/Physical Classification of water The three main forms of water in the soil are gravitational water, capillary water and hygroscopic water. Gravitational water - Present in the macro pores and moves freely downwards under the influence of gravity beyond root zone and not available to plants. This is excess water or even called as superfluous water. Water held between 0.0 to 0.33 bars (0 to −33 kPa/0 – 33 centibars) soil moisture tension, free and in excess of field capacity, which moves rapidly down towards the water table under the influence of gravity is termed as gravitational water. Even though the gravitational water is retained with low energy, it is of little use to plants, because it is present in the soil for only a short period of time and while in the soil, it occupies the larger pores i.e., macro pores, thereby reducing soil aeration. It can cause upland plants to wilt and die because gravitational water occupies air space, which is necessary to supply oxygen to the roots. Therefore, its removal from the soil profile through natural drainage is generally regarded as a pre-requisite for optimum plant growth and development. Factors affecting gravitational water Texture: Plays a great role in controlling the rate of movement of gravitational water. The flow of water is proportional to the size of particles. The bigger the particle, the more rapid is the flow or movement. Because of the larger size of pore, water percolates more easily and rapidly in sandy soils than in clay soils. Structure: It also affects gravitational water. In platy structure movement of gravitational water is slow and water stagnates in the soil. Granular and crumby structure helps to improve gravitational water movement. In clay soils having single grain structure, the gravitational water, percolates more slowly. If clay soils form aggregates (granular structure), the movement of gravitational water improves. 2. Capillary water: Capillary water is held in the capillary pores (micro pores) or < 0.06 mm. Capillary water is retained on the soil particles by surface forces. It is held so strongly that gravity cannot remove it from the soil particles. This water is called as water of cohesion. As the name suggests capillary water is held in the pores of capillary size i.e., micro pores around the soil particles by adhesion (attraction of water molecules for soil particles), cohesion (attraction between water molecules) and surface tension phenomena. The molecules of capillary water are free and mobile and are present in a liquid state. Due to this reason, it evaporates easily at ordinary temperature though it is held firmly by the soil particle; plant roots are able to absorb it. Capillary water is, therefore, known as available water. The capillary water is held between 1/3 or 0.33 and 31 bars. i.e., it is held between field capacity (0.33 bars or −33 kPa) and hygroscopic coefficient (31 bars or −3100 kPa). However, the water within the capillary range is not equally available i.e., it is readily available starting from 0.33 bars up to a certain point often referred to as critical soil moisture level (for most crops it varies between 20 to 50% depletion of available soil moisture) and thereafter up to 15 bars (−1500 kPa) it is slowly available. Further below, when the soil exerts tensions between 15 bars and 31 bars, the water is held very tightly in thin films and is practically not available for plant use. Lecture No-9 Crop Water Requirement Water Requirement Water requirement of a crop is the quantity of water needed for normal growth and yield and may be supplied by precipitation or by irrigation or by both. Water is needed mainly to meet the demands of evaporation (E), transpiration (T) and metabolic needs of the plants, all together known as consumptive use (CU). CU = E +T + Water needed for metabolic purposes. Water used in the metabolic activities of plant is negligible and is often less than 1% of the quantity of water passing through the plant. Evapotranspiration is, therefore, considered as equal to consumptive use. Different losses like percolation, seepage, runoff etc., occur during transport and application of irrigation water. Water is needed for special operations such as land preparation, transplantation, leaching etc. Water requirement of a crop (WR), therefore, includes evapotranspiration, application losses and water needed for special purposes. WR= ET + Application losses + Water for special purposes WR = ET or Cu + Application losses + Special needs Water requirement is a demand whereas the supply consists of contribution from irrigation water, effective rainfall (ER) and soil profile contribution including that from shallow water table (S). Definition : It is defined as the quantity of water regardless of its source, required by a crop or diversified pattern of crops in a given period of time for its normal growth & development under field conditions at a given place. In other words it is the total quantity of water required to mature an adequately irrigated crop. It is expressed in depth per unit time. Water requirement, if considered as a demand, it includes the quantity of water needed to meet the losses due to evapotranspiration (ET), plus the losses during the application of irrigation water (unavoidable losses) and the additional quantity of water required for special operations such as land preparation, transplanting, leaching of salts below the crop root zone, frost control etc. It can also be expressed in supply terms as WR = Irr + ER + ΔS + GWC Where: Irr = Total depth of irrigation water during crop life ER = Effective rainfall received during crop life ΔS = Profile water use i.e., difference in soil moisture in the crop root zone at the beginning and end of the crop GWC = Groundwater contribution, if any. Accurate crop water requirement data is essential in irrigated agriculture for: 1. Economic appraisal of irrigation projects 2. Design and operation of irrigation schemes 3. Fixing cropping patterns and irrigated areas 4. Irrigation scheduling to crops 5. Efficient use of limited water Irrigation Requirement Irrigation requirement is the total amount of water applied to a field to supplement rainfall and soil profile contribution to meet the water needs of crops for optimum growth. Irrigation requirement = WR – (ER + S) The net irrigation requirement is the amount of irrigation water just required to bring the soil moisture content in the root zone depth of the crops to field capacity. Thus the net irrigation requirement is the difference between field capacity and soil moisture content in the root zone before irrigation. Gross irrigation requirement is the total of net irrigation requirement and other losses such as conveyance, distribution and application. Factors Affecting Water Requirement The water requirement of any crop is dependent upon Crop Factors: variety, growth stage, duration, plant population and growing season Varieties of the same crop differ in duration, rooting pattern and canopy structure. The variety, with longer duration obviously requires more water for completion of the life cycle. During the growth of crop, consumptive use is maximum during flowering and grain filling in cereals compared to that in seedling stage. Crops differ in producing leaf area and covering the ground. Higher the leaf area index, more is the evapotranspirtion. Evaporanspirtion also differs with height of the crop. Tall crops intercept more solar radiation and have more evapotranspiration than short crops. Soil factors: texture, structure, depth, topography Evaporation from soils differs due to their difference in hydraulic conductivity, reflectivity and thermal conductivity. At higher moisture regimes, coarse textured soils have higher hydraulic conductivity than fine textured soils. With the result, evaporation is faster in coarse textured soils under intermittent wetting and drying. Evaporation mostly occurs from the top 5 cm of soil and soil structure up to 15 cm depth influences evaporation through its influence on water supply to evaporation site. Higher percentage of aggregates of more than 1.0 mm diameter reduce the upward movement of water and hence evaporation. Formation of ridges and furrows reduces evaporation due to the presence of large sized aggregates. Colour of the soil also has considerable influence on evaporation from the soil surface. Dark coloured soils absorb more of solar radiation and thus increase evaporation. Can Evaporimetry Small cans of one litre capacity (14.3 cm height and 10. cm diameter) are used to indicate evaporation from the cropped field. These cans are painted white and covered with 6/20 size mesh. An indicator pointer is fixed at 1.5 the can is filled up with water to pointer level and kept at the crop height. Evaporation from can is directly related to crop evapotranspiration. Critical Stage Approach In each crop, there are some growth stages at which moisture stress leads to irrevocable yield loss. Moisture sensitive stages of important crop) Crop Important moisture sensitive stages Rice Panicle initiation, flowering Wheat Crown –root initiation, joining, milking Sorghum Seedling, flowering Maize Silking, tasseling Pearl millet Flowering, panicle initiation Finger millet Panicle initiation, flowering Groundnut Rapid flowering and pod formation Redgram Greengram Blackgram Sugarcane Formative stage Sesamum Blooming stage to maturity Sunflower Two weeks before flowering to two weeks after flowering Safflower From rosette to flowering Simple Techniques for Irrigation Scheduling Soil –cum-sand Miniplot Technique In this method one-cubic-metre pit is dug in the middle of the field. About five per cent of sand by volume is added to the dug soil, mixed well and the pit is filled up in the natural order. Crops are grown as usual in the entire area of the field including the pit area. The plants in the pit show wilting symptoms earlier than the other plants in the remaining area. Irrigation is scheduled as soon as wilting symptoms appear on the plants in the pit. Sowing High Seed Rate In an elevated area, one-square-metre plot is selected and crop is grown with four times thicker than normal seed rate. Because of high plant density, plants show wilting symptoms earlier than in the rest of the crop area indicating the need for scheduling of irrigation. Feel and Appearance Method Moisture content can be roughly estimated by taking the soil from root zone into the hand and making it into a ball. It requires a lot of experience to estimate the soil moisture by this method and rough guidance is given in Table 9. Irrometers or Tensiometers Irrigation can be scheduled based on soil moisture tension. Tensiometers (irrometers) are installed at specified depth in the root zone. When the soil moisture tension reaches a specified value (0.5, 0.75 or 1.0 bars etc) irrigation is given. These are generally used for irrigation orchards, especially in coarse textured soils. However, irrometers do not give any information on the amount of irrigation water to be applied at each irrigation. Water Use Efficiency Water-use efficiency is defined as the yield of marketable crop produced per unit of water used in evapotranspiration. WUE= Y/ET Where WUE is water-use efficiency (kg/ha mm); Y the marketable yield (kg/ha) and ET is evapotranspiration (mm). If yield is proportional to ET, water-use efficiency has to be a constant but it is not so. Actually, Y and ET are influenced independently or differently by crop management and environment. Yield is more influenced by crop management practices, while ET is mainly dependent on climate and soil moisture. Fertilization and other cultural practices for high crop yields usually increase WUE, because they relatively increase crop yield more than crop water-use. Also any increase in water-use accompanying fertilization is often negligible. Crop production can be increased by judicious irrigation without markedly increasing ET. Under an optimal water supply, ET is not dependent on the kind of plant canopy, provided the soil is adequately covered with crop. Increasing the amount of plant canopy has, therefore, little or no effect on ET. Obviously, any practice that promotes plant growth and the more efficient use of sunlight in photosynthesis without causing a corresponding increase in ET will increase WUE. Factors Affecting WUE Type of the Plant There are considerable differences between plant species to produce a unit of dry matter per unit amount of water used resulting in widely varying values of WUE. Water –use efficiency of different crops Crop Water requirement (mm) Grain yield (kg/ha) WUE (kg/ha mm) Rice 2,000 6,000 3.0 Sorghum 500 4.500 9.0 Pearl millet 500 4,000 8.0 Maize 625 5,000 8.0 Groundnut 506 4,680 9.2 Wheat 280 3,534 12.6 Finger millet 310 4,137 13.4 There are also differences in WUE between varieties of the same crop. Selection of properly adopted crops, with good rooting habits, low transpiration rates and improved energy consumption in photosynthesis will increase WUE. Climate Conditions Weather affects both Y and ET. Manipulation of climate to any great extent is not possible at present. However, ET can be reduced by mulching, use of antitranspirants etc., to a limited extent, but may not be economical or practical. Weed control is the most effective means of reducing ET losses and increasing the amount of water available to the crop thereby increasing WUE. Soil Moisture Content Inadequate supply of soil moisture as well as excess moisture supply to the crop have an adverse effect on plant growth and productivity and are, therefore, conductive to low WUE. For each crop and combination of environmental conditions, there is a narrow range of soil moisture levels at which WUE is higher than with lesser or greater supply of water. Proper scheduling of irrigation will increase WUE. QUALITY OF IRRIGATION WATER Irrigation water contains different impurities in varying concentrations. The suitability of irrigation water mainly depends on the amount and type of salts present in the water. The main soluble constituents are calcium, magnesium, sodium as cations and chloride, sulphate, bicarbonate as anions. The other ions present in minute quantities are boron, selenium, molybdenum and fluorine which are harmful to animals fed on plants grown with excess concentration of these ions. Quality of irrigation water is judged with three parameters: (1) total salt concentration, (2) sodium adsorption ratio and (3) bicarbonate and boron content. Total salt Concentration Salt content of irrigation water is measured as electrical conductivity (EC). Conventionally, water containing total dissolved salts to the extent of more than 1.5 m mhos/cm has been classified as saline. Saline waters are those which have sodium chloride as the predominant salt. Brackish water contains more of salts other than sodium chloride. Scientifically, brackish water is one that is contaminated with acids, bases, salts or organic matter, whereas saline water contains mainly dissolved salts. Based on EC, irrigation water is classified as shown in Table 13. Sodium Adsorptions Ratio and Boron Content In addition to EC, which has been used as a main criterion to determine the quality of irrigation water, sodium adsorption ratio (SAR), residual sodium carbonate (RSC) and boron content are also used to find suitability of irrigation water. Classification of irrigation water based on total salt content Class EC (m mhosicm) Quality characterization Soils for which suitable C1 < 1.5 Normal waters All soils C2 1.5-3 Low salinity waters Light and medium textured soils C3 3.5 Medium salinity waters Light and medium textured soils for semi-tolerant crops C4 5.10 Saline waters Light and medium textured soils for tolerant crops C5 < 10 High salinity waters Not suitable Irrigation water which contains more than 3 ppm boron is harmful to crops, especially on light soils. Classification of irrigation water based on boron content is given in Table. Classification of irrigation water based on boron content Class Boron (ppm) Characterization Soils suitable B1 < 3 Normal water All soils B2 3-4 Low boron waters Clayey soils and medium textured soils B3 4-5 Medium boron waters Heavy textured soils B4 5-10 Boron waters Heavy textured soils B5 >10 High boron waters Not suitable QUALITY OF WATER OF DIFFERENT SOURCES Water quality of most of the Indian rivers is good with EC values less than 0.7 m mhos/cm except in Krishna (1.4), Hagari (1.6) and Tungabhadra (1.7) rivers. Water quality of most of the tanks, lakes etc., is fairly good except in those which are fed by streams passing through salt-affected areas. Quality of ground water is influenced by soil characteristics, water table and rainfall of the region. Water quality in semi arid and arid regions is generally poor with high salt content. IRRIGATION WITH POOR QUALITY WATER Crop growth in soils irrigated with poor quality water decreases due to increased osmotic stress and poor physical condition of highly dispersed sodic soils. The degree of harmful effect varies with the crop, variety, stage of growth and management practices. The adverse effect of poor quality irrigation water can be minimized by improving water quality and by suitable soil and irrigation management practices. Improving Water Quality The harmful effects of poor quality irrigation water can be minimized by adding chemicals which precipitate the harmful constituents. There appears to be no practical method to reduce the total concentration of salt in irrigation water of large irrigation projects. Drainage: Removal of excess water from the surface or below the surface of the soil so as to create favourable conditions for plant growth. Causes of Water Logging 1. Intensive rains 2. Floods 3. Soil slope 4. Bunds 5. Defective irrigation 6. Seepage from unlined canals. Effects of ill drained conditions: 1. Lack of aeration of soil. 2. Restricted root growth and lodging problems 3. Difficult to till the land 4. Increase in salinity in top layers of soil. All crops including rice require well drained conditions. Crops like maize mustard are very sensitive to water logging or ill drainage even for a short period. Mid season drainage is important in rice. 2. Drainage can be surface drainage (or) Sub surface drainage. Benefits of drainage 1. Helps in soil ventilation/aeration 2. Facilitates timely tillage operations. 3. Better and healthy root growth. 4. Favours growth of soil microorganism (better mineralization) 5. Warming up for optimum soil temperature maintenance. 6. Promotes leaching and reduce logging. 7. Improves anchorage and reduce lodging. 8. Improves soil structure and decrease soil erosion. 9. Improves sanitary and health conditions and makes rural life happy. Health hazards for human and animals Sl No. Weed host Diseases 1 Argemone mexicana Alkaloid Sanguinarin Dropsy in humans due to its mixing in mustard seeds, Blindness, Death 2 Parthenium hysterophorus Skin itching, asthama, fever, septicemia 3 Ambrosia sp. Hay fever 4 Brush weeds African sleeping sickness 5 Pistia lanceolate, Salvinia auriculata Malaria, Encephalitis and Filaria Suffocation, Asphyxation Quality Reduced quality of produce Mix with crop seeds during harvest Cuscuta in Lucerne, wild rice in rice, Solanum nigrum in cowpea or soybean; Avena fatua in cultivated oats; Phalaris minor in wheat; Classification of weeds There are over 2,50,000 - 3,00,00 plant species around the world, of which 25,000-30,000 behave as weed and 250 weed species are prominent in agricultural and non- agricultural system. It becomes necessary that these should be studied in various aspects so that ways and means may be devised to control them and utilize them. There are many ways weeds can be grouped for the convenience of planning, interpreting and recording control measures against them. Some important classifications of weeds used by the weed scientists the world over for different purposes are follows: I. Botanical/Taxonomic classification: II. Classification according to ontogeny/life cycle of weeds: Depending upon their life cycles, weeds can be classified as annuals, biennials and perennials. Weed based on life cycle ……………………………………………………………………………………………………… Annuals/ Seasonal Biennials/ Bi seasonal Perennials/ Multi seasonal …………………………………………. Summer annuals Usual mode of reprdn. Depth of root system Rainy season annuls Winter annuals An annual weed can be either being a summer annual or a winter annual depending upon part of the year when it puts forth its major growth. Summer annuals; Ageratum conyzoides, Amaranthus viridis/spinosus, Trianthema portulacastrum/monogyna spp.- carpet weed, Setaria glauca-foxtail, Degera arvensis- Digera, Dactyloctenium aegyptium are typical weeds. Winter annuals: Chenopodium album- Lambsquarters; Phalaris minor/paradoxa; Avena fatua/ludoviciana; Vicia spp- vetches are typical weeds. Amaranthus virdis-may grow round the year near irrigated channels and most places, but primary it is a summer annual. Rainy/Wet season annuals: Germinate during rainy/wet season when there is ample moisture in the soil. Ageratum conyzoides; Amaranthus hybridus/spinosus; Commelina benghalensis; Digera arvensis; Setaria glauca; Trianthema monogyna/portulacastrum. Biennial weeds: Biennial weeds complete their life cycle in two seasons/ years: They take more than one year but less than two years. In the first year they remain vegetative/ rosette stage and in the second year they produce flowers and set seeds. The usual feature biennial weeds to flower in the second year of growth limits their dispersal crop seeds, very much. Ex: Cichorium intybus- Cichory; Tribulus terrestris-Puncture wine weed, Cirsium vulgare (bull thistle) are found in cropped areas. Simple perennial Shallow perennial Creeping perennial Deep rooted perennial Woody perennial Daucus carota-Wild carrot, Altenanthera echinata/pungens are found in non cropped areas. Perennial weeds: They grow for more than two years before they wither away or die-up. They flower for the first time in the second year of their growth and then flower each year regularly and grow indefinitely from the same root system. Besides through seeds, the perennial weeds reproduce vegetative from underground, specialized structures. Weed species within the genus may show considerable variation. Some plants may show annual habit i.e., Cyperus iria/difformis, Physalis minima, Digitaria sanguinalis. Panicum maximum, Agropyron repens are the good examples of perennial weeds. Classification according to cotyledon character: The discovery of 2,4-D (MCPA) as highly selective trasnlocated herbicide in 1940’s gave strong recognition to two great class of weeds namely A) Monocotyledonous: The seeds have one cotyledon and cannot be split into two halves. Monocot plants include cereal crop, all grasses, sedge, water hyacinth, sugarcane, palm, orchid cattail, banana, iris and lily. It should be remembered that all grasses are monocots, but all monocots, are not grasses. Monocot weed may be annual, biennial or perennial in nature They are further divided into grasses and sedges. a) Grasses: Several grassy weeds are Phalaris minor, Cynodon dactylon, Digitaria abyssinica, Polygon monspeliensis, Avena fatua/ludoviciana/sterilis, Poa annua, Commelina and Cynotis Grasses may be Narrow leaved monocot: the majority of grasses are narrow leaved ones. Ex. Cyanodon, Digitaria sanguinalis, Avena fatua, Poa annua Broad leaved monocot: They have broad leaved plants with palmate like venation, Commmelina, Cynotis, Eichhornia spp are monocot grass weeds but have broad leaves. Weed Management Weed management methods can be divided into two 1. Preventive method 2. Curative/ remedial method: Curative method is sub divided into eradication and control Weed Eradication: Eradication is the ideal method of weed control, rarely achieved. Eradication is complete elimination all live plants, plant parts and seeds from an area. Once eradicated, the weed should not reappear unless re introduced to the area. Need for eradication: Some are undesirable under variety of situation if such weeds are left without extermination, they produce seeds and the axiom “ One year seedling seven years weeding becomes absolutely true” So when and where new weed species is found, it must be destroyed immediately before its multiplication, dispersion and acclimatization. Weed prevention: Weed prevention comprises all measures which deny entry/establishment of weed in an area. • It includes farm hygiene that prevents every year production of seeds, tubers and rhizomes of weed species already present on the farm. • Any physical/chemical method adopted with objective of not allowing weeds to set viable seeds is to be considered of a part of weed prevention. • In other words, all practices that help to discourage the weed from becoming a problem over a time called prevention. • It reduces the farmers efforts in controlling weeds later by physical/ chemical / other methods and that is why preventive measures are “cost effective” • “Prevention is better than cure”- a popular axiom Pulses 15-60 Jute 30-45 Green gram/Black gram/ Cowpea 15-30 Vegetables Chick pea 30-60 Cauliflower/cabbage/ Tomato 30-45 Peas 30-60 Okra 15-30 Soybean 20-45 The following preventive measures are suggested for adoption, wherever possible and practicable Prevention by use of weed free crop seed: Weeds spread on the farm lands with certain crops seed. Ex. Avena fatua, Brassica with small grains. Lucerne, berseem and other small seed forage legumes and grasses are particularly prone to easy contamination with specific seed of similar size and shape. Objectionable weed species and their maximum permissible limits and total weed species permissible limits in certified seeds of certain crops. Crop Objectionable weed Permissible weed admixture limit Objectionable Total Oryza sativa Wild rice (0. Satuiva. Var. futua) 0.01 % 0.1 % T. aestvum Convoluulus arventsis 0.01 % or (5 seed/kg of crop seed) 0.1% B. campestris , B. juncea Argemone mexicana 0.1% 0.5% Trifolium alexandrium (Egyptian clover) Chicory (Chichorium intybus) 0.05 % 20seeds/kg crop seed 0.05% Medicago sativa Cuscuta spp. 0.05% 20seeds/kg crop seed 0.05% Lettuce Lactuca sativa) Wild lettuce (L.serriock) 0.1 0.2% Cucurbit Cucurbita sp) Wild cucurbit 0.0 0.0 Okra (Ablemoschus esculentus) Wild okra (Ablemoschus spp) 0.0 0.0 ➢ Prevention by use of well decomposed FYM/ Compost/ Vermicompost: ➢ Isolation of introduced livestock to prevent spread of weed seeds form digestive tract ➢ Use of clean farm equipments and cleaning equipments including combiners, cultivator’s etc. ➢ Cleaning irrigation water before it enters a field. ➢ Moving and other appropriate weed control practices to prevent seed production on irrigation ditch banks. ➢ Inspection of imported nursery stock for seeds, seeds and vegetative reproductive organs. ➢ Inspection and cleaning of imported gravel, sand and soil. ➢ Special attention to fence lines. Roads, field boundaries and irrigation channels etc. as source of weed. ➢ Field should be regularly be surveyed to indentify new weeds. When indentified, small patches of new weeds should be treated to prevent growth and further dispersal. ➢ Keep non crop area clean ➢ Prevention by weed laws/ legal measures: They are important in reducing the spread of weeds. Quarantine laws. Ex: Parthenium, Lantana, Phalaris minor they are all exotic weeds entered Indian because on quarantine/ legal measures Weed Control Definition: 1) Weed control is the process of limiting infestations so that crops can be grown profitably or other operations conducted efficiently. Weed control encompasses those practices where by weed infestations are reduced, but not necessarily eliminated Weed control is a matter of degree ranging from poor to excellent this is dependent on characteristics of weeds (s) included and effectiveness of the method(s) of control used. The various methods of weed control are grouped as cultural, physical, biological and chemical methods. In other words weed control methods are grouped into A) Mechanical and manual • Tillage • Hand pulling/weeding • Hoeing • Mowing • Flooding B) Cultural/ ecological C) Biological a) Flaming /burning: Many plant processes are susceptible to high temperature disruption attributed to coagulation and denaturation of protein, increasing cell permeability and enzyme inactivation. Photosynthesis is stopped or decreased. Initially thermal disruption of cellular membranes takes place followed by dehydration of cells. Thermal death point for most plant tissue is between 45 and 55 C after prolonged period. b) Flame cultivation: When fire is used to burn the crop residue (cotton sugarcane, etc.) for selective weed control of annual weeds (BLW and grasses) in crop rows is called as flame cultivation. Cotton plant can resist the flames if it is properly controlled and hence flame cultivation is adopted in cotton. Controlled burning is done with the help of hand operated vapouring burners. Flame torches and flame throwers. B) Solarizaiton (Solar heating): It is feasible to use the heat of the sun to control weeds in a process called solarization. Weeds seed germination is suppressed by high soil temperatures (55-60C) and seedlings are killed. Transparent opaque polyethylene sheets raise soil temperature above the thermal death point for most seedlings and many sees. The sequence of soil solarization involves I. Covering the soil with transparent polyethylene (PE) film during hottest part of summer months for longer tenure. II. It has potential of raising the surface soil temperature up to 10-120 C over the un filmed control fields, which is adequate for desiccating numerous weed seeds present in the top 5 cm layer. III. The sudden rise in soil temperature is due to hindrance created by the film in permitting back radiation of solar long waves from the soil and prevention of heat loss otherwise incurred in the evaporation of soil moisture. IV. Thin PE sheet of 20-25 mm thickness are ideal for achieving the desired rise is soil temperature, though the thicker ones up to 100 mm thickness has also been successfully used. One Pre –filming irrigation has been found to augment soil solarization effect, both by trapping more heat and by making the weed seeds more susceptible to thermal effects. Several annual grass weed (including P. milnor and Avena spp) as well as BLW’s are susceptiable to soil solarisaion. Weeds with hard seed coats, like Melilotus spp. are difficult to damage by soil solarisation. Perennial weeds are only stunted because not all weeds are equally susceptible to soil solarization. Soil solarization improves crop yield by aiding the control of weeds as well as by damaging insect pest and disease causing organisms. Besides improving the nutrient and biological activity of the soil, Drawbacks: Costly, justified in high value crops can be practiced in nursery. 2 Mulching: Mulching excludes light and prevents shoot growth. Mulches increase soil temperature and may promote better plant growth. It is effective against perennial weeds like C. dactylon, Sorghum halepense etc. main advantage is that they suppress the weeds and eliminates the need for intercultivation. Plastic mulches are found to be effective in controlling weeds in wide spaced crops (cotton, tomato, brinjal, Sugarcane etc.) Flooding: Flooding creates anaerobic condition,which prevents /reduces weed seed germination, and root reparation of already germinated weed and kill plants by reducing oxygen supply for growth, it could be practiced in cropped and non cropped situations if cost economics permits. Ex. Field bind weed and Cynodon can be controlled by flooding in rice Striga in sugarcane, flooding during flowering is most critical. Trap and catch crop : Trap and catch crops should be included in crop rotation particularly for controlling parasitic weed Striga and Orobanche but not for cuscuta. There s no trap or catch crop for Cuscuta. Trap Crops are nothing but false hosts, which exude Striga geminaion stimulant and induce Striga seed germination, but after germination, Striga may die-out for want of /lack if attachment with host roots. This is called suicidal germination. Cotton, soybean, sunflower, cowpea, jute, pigeon pea, chick pea, chick pea, groundnut are trap crop for striga,. sunilarly pepper, seasame, cotton, soybean, lucerne, horse ram, sorghum, niger, brinjal, chickpea are the trap crops for Orobanche. Trap crops are not usually scarified but harvested as crop. Catch crops: On the contrary are parasitic weed susceptible varieties of crop which are grown and ploughed into soil prior to flowering of parasitic weeds and sowing of a crop of principle interest. Ex. Sudan grass (Sroghum sudanense) is effect catch crop and growing it for 5 weeks before cutting and sowing of sorghum in the stubble reduced the infestation of Stiga hermonthica. For Orbanche, toria can be used. Adoption of stale seed bed: Passing light harrow ( or use of paraquat) to disturb weeds after land preparation but before seedling. Here,1-2 flushes of weeds are destroyed before planting of any crop. If a finely prepared seed bed is withheld form planting and it contains adequate moisture in its top 4-5 cm of soil, a flush of young weed seedling will appear on it in about a week’s time . these weeds are destroyed either by contact herbicide like paraqate/ by light harrowing. Smother cropping (competitive crops): These crop germinate quickly and develop large canopy, capable of efficient photosynthesis in relatively short period. They possess both surface and deep roots. They suppress weed seedling by excluding light beneath and utilizing nutrients form the soil. Biological weed control Biological weed control involves the utilization of natural enemies (bio-agent ) for the control of certain weeds. In biological control program, the natural enemies are introduced, encouraged and multiplied by artificial means and disseminated by man with his own efforts instead of leaving it to nature and thus differ from natural control. The objectives of biological control are not eradication but rather the reduction and regulation of weed population below the level of economic injury . Small/narrow span of activity: The span of activity of bio agent in most cases is small/ narrow, whereas weeds may grow all through the year. For example, Parthenium hysterophorus grows all through the year, but Zygogramma bicolarata, the bio agent is active only during rainy season for a period of 2-3 moths starting from July. Conflict of interest over target weed: the biological control for certain weed may have limited acceptance by the people because it may lead to conflict of interest over whether a plant is weed at all times or considered a crop or useful plant in other situation. For example: Lantana is mainly a roadside weed but useful shrub to the farmers since it is available free of cost for making shade in some weak stem climber crops namely bitter gourd, pointed gourd, ridge gourd etc. Controversy is also on biological control of Chromolaena odorata which is considered an important plant for quick rejuvenation of bush fallow lands. Once it is removed, Panicum maximum which is much more difficult to manage in cultivation takes over. Lecture 16 and 17 Crop Growth and Development Crop Growth and Development Factors affecting crop production – climatic – edaphic - biotic- physiographic and socio economic factors I. Internal factors Genetic factors The increase in crop yields and other desirable characters are related to Genetic make up of plants. • High yielding ability • Early maturity • Resistance to lodging • Drought flood and salinity tolerance • Tolerance to insect pests and diseases • Chemical composition of grains (oil content, protein content) • Quality of grains (fineness, coarseness) • Quality of straw (sweetness, juiciness) The above characters are less influenced by environmental factors since they are governed by genetic make-up of crop. 2. External factors A. Climatic B. Edaphic C. Biotic D. Physiographic E. Socio- economic A. Climatic Factors Nearly 50 % of yield is attributed to the influence of climatic factors.The following are the atmospheric weather variables which influences the crop production. 1. Precipitation • Precipitation includes all water which falls from atmosphere such as rainfall, snow, hail, fog and dew. • Rainfall one of the most important factor influences the vegetation of a place. • Total precipitation in amount and distribution greatly affects the choice of a cultivated species in a place. In heavy and evenly distributed rainfall areas, crops like rice in plains and tea, coffee and rubber in Western Ghats are grown. • Low and uneven distribution of rainfall is common in dryland farming where drought resistance crops like pearl millet, sorghum and minor millets are grown. • In desert areas grasses and shrubs are common where hot desert climate exists • Though the rainfall has major influence on yield of crops, yields are not always directly proportional to the amount of Precipitation as excess above optimum reduces the yields • Distribution of rainfall is more important than total rainfall to have longer growing period especially in dry lands. 2. Temperature • Temperature is a measure of intensity of heat energy. The range of temperature for maximum growth of most of the agricultural plants is between 15 and 40ºC. • The temperature of a place is largely determined by its distance from the equator (latitude) and altitude. • It influences distribution of crop plants and vegetation. • Germination, growth and development of crops are highly influenced by temperature. • Affects leaf production, expansion and flowering. • Physical and chemical processes within the plants are governed by air temperature. • Diffusion rates of gases and liquids changes with temperature. • Solubility of different substances in plant is dependent on temperature. • The minimum, maximum (above which crop growth ceases) and optimum temperature of individual’s plant is called as cardinal temperature. Crops Mini temp Optimum temp Max temp Rice 10 32 36-38 Wheat 4.5 20 30-32 Maize 8-10 20 40-43 Sorghum 12-13 25 40 Tobacco 12-14 29 35 1. Soil moisture • Water is a principal constituent of growing plant which it extracts from soil • Water is essential for photosynthesis • The moisture range between field capacity and permanent wilting point is available to plants. • Available moisture will be more in clay soil than sandy soil • Soil water helps in chemical and biological activities of soil including mineralization • It influences the soil environment Eg. it moderates the soil temperature from extremes • Nutrient availability and mobility increases with increase in soil moisture content. 2. Soil air • Aeration of soil is absolutely essential for the absorption of water by roots • Germination is inhibited in the absence of oxygen • O 2 is required for respiration of roots and micro organisms. • Soil air is essential for nutrient availability of the soil by breaking down insoluble mineral to soluble salts • For proper decomposition of organic matter • Potato, tobacco, cotton linseed, tea and legumes need higher O 2 in soil air • Rice requires low level of O 2 and can tolerate water logged (absence of O2) condition. 3. Soil temperature • It affects the physical and chemical processes going on in the soil. • It influences the rate of absorption of water and solutes (nutrients) • It affects the germination of seeds and growth rate of underground portions of the crops like tapioca, sweet potato. • Soil temperature controls the microbial activity and processes involved in the nutrient availability 4. Soil mineral matter • The mineral content of soil is derived from the weathering of rocks and minerals as particles of different sizes. • These are the sources of plant nutrients eg; Ca, Mg, S, Mn, Fe, K etc 5. Soil Organic matter • It supplies all the major, minor and micro nutrients to crops • It improves the texture of the soil • It increases the water holding capacity of the soil, • It is a source of food for most microorganisms • Organic acids released during decomposition of organic matter enables mineralisation process thus releasing unavailable plant nutrients 6. Soil organisms: • The raw organic matter in the soil is decomposed by different micro organisms which in turn releases the plant nutrients • Atmospheric nitrogen is fixed by microbes in the soil and is available to crop plants through symbiotic (Rhizobium) or non-symbiotic (Azospirillum) association 7. Soil reaction (pH) • Soil reaction is the pH (hydrogen ion concentration) of the soil. • Soil pH affects crop growth and neutral soils with pH 7.0 are best for growth of most of the crops • Soils may be acidic (<7.0), neutral (=7.0), saline and alkaline (>7.0) • Soils with low pH is injurious to plants due high toxicity of Fe and Al. • Low pH also interferes with availability of other plant nutrients. C. Biotic Factors Beneficial and harmful effects caused by other biological organism (plants and animals) on the crop plants 1. Plants • Competitive and complimentary nature among field crops when grown together • Competition between plants occurs when there is demand for nutrients, moisture and sunlight particularly when they are in short supply or when plants are closely spaced • When different crops of cereals and legumes are grown together, mutual benefit results in higher yield (synergistic effect) • Competition between weed and crop plants as parasites eg: Striga parasite weed on sugarcane crop 2. Animals • Soil fauna like protozoa, nematode, snails, and insects help in organic matter decomposition, while using organic matter for their living • Insects and nematodes cause damage to crop yield and considered as harmful organisms. • Honey bees and wasps help in cross pollination and increases yield and considered as beneficial organisms • Burrowing earthworm facilitates aeration and drainage of the soil as ingestion of organic and mineral matter by earthworm results in constant mixing of these materials in the soils. • Large animals cause damage to crop plants by grazing (cattle, goats etc) D. Physiographic factors: • Topography is the nature of surface earth (leveled or sloppy) is known as topography. Topographic factors affect the crop growth indirectly. • Altitude – increase in altitude cause a decrease in temperature and increase in precipitation and wind velocity (hills and plains) • Steepness of slope: it results in run off of rain water and loss of nutrient rich top soil • Exposure to light and wind: a mountain slope exposed to low intensity of light and strong dry winds may results in poor crop yields (coastal areas and interior pockets) E. Socio-economic factors • Society inclination to farming and members available for cultivation Types of Sequential Cropping Double Cropping: Cultivation of two crops in succession on a piece of land in a year. Triple Cropping: Cultivation of three crops in succession on a piece of land in a year. Quadruple Cropping: Cultivation of four crops in succession on a piece of land in a year. Ratoon Cropping/Ratooning: Cultivation of crop re-growth after its harvest is rationing. It is also a type of sequential cropping. In this, more than one harvest is done from one sowing/planting. Thus, ratooning consists of allowing stubbles of the original crop after harvesting and to raise another crop. Intercropping Growing two or more crops simultaneously on the same piece of land.Crop intensification is in terms of both time and space dimensions. Main Crop/Base Crop:It is one which is planted at its optimum population in an intercrop situation and the second crop is planted in between the rows of main or base crop, with a view to obtain some extra inter crop yield without sacrificing the main or base crop yield. Intercrop:The short duration crop is raised in widely spaced crop for getting an additional income from the same piece of land. leFig: Main Crop and intercrop Component Crop: It is used to refer either of the individual crops making the intercropping situation. Benefits of Intercropping 1. Better utilization growth resources like light, nutrients and moisture. 2. Economy in space and time. 3. Suppression of weeds. 4. Serves as insurance against failure of any one of the component crops. 5. Reduces soil crust formation. 6. Improves soil fertility. 7. Ecological stability. 8. Controlling of soil erosion. 9. Serves as physical support or shading to some crops. 10. Additional yield from unit area. 11. Additional income. 12. Provides farmer's daily needs. 13. Provides employment and distribution of labour. 14. Cultivation practices for main crop supplement the requirement of companion crop. 15. Control of pests and diseases. Limitations of Intercropping 1. Labour intensive. 2. Differential maturity and problem of harvesting. 3. Serves as alternate hosts for pests and diseases. 4. Control of pests, diseases and weeds is difficult. 5. Problem for intercultural operations. 6. Mechanization is difficult. 7. Competitive effects among component crops. 8. Allelopathic effect. Types of Intercropping Mixed Intercropping/Mixed Cropping :Growing of two or more crops simultaneously on the same piece of land with no distinct row arrangement. Row Intercropping: Growing of two or more crops simultaneously on the same piece of land with distinct row arrangement. It is simply referred as ‘intercropping’. [e2Row Intercropping lazRow Intercropping. Fig: Row Intercropping. Patch Intercropping:Growing of two or more crops simultaneously on the same piece of land in patches. Criteria for Selection of Crops for Intercropping System Care should be taken to select the crops with different growth habits, root growth, duration and families. The following points to be considered while selecting crops for intercropping system. 1. Tall growing crops with short growing crops. 2. Bushy crops with erect growing crops. 3. Fast growing crops with slow growing crops. 4. Deep rooted crops with shallow rooted crops. 5. Short duration crops with long duration crops. 6. Legume crops with non-legume crops. 7. Crops should have least allelopathic effect. 8. Crops selected should be of different families to avoid pests and diseases. Crop Kotation Growing of different crops alternatively on the same piece of land in a definite sequence or process of growing different crops in succession on a piece of land in a specific period of time with an objective to get maximum profit from least investment without impairing the soil fertility.