Applied Soil Physics: Understanding Soil Heterogeneity and Its Impact on Plant Growth - Pr, Study notes of Agricultural engineering

Download Applied Soil Physics: Understanding Soil Heterogeneity and Its Impact on Plant Growth - Pr and more Study notes Agricultural engineering in PDF only on Docsity! “ Soil Heterogeneity ‘. among profiles and roots ‘ i WELCOME to Applied Soil Physics, CSS 340 Soil Physical Conditions and their Control of Sustainable Soil and Plant Production Row Crops, Turfgrass and Cellulosic Biomass Including Environmental Applications Spring 2012 Course Objectives: 1. CSS340 is designed to identify key physical properties that control the transport of soil water, solutes, organics, gases, and thermal conditions affecting plant growth and development. 2. CSS340 is designed to introduce students to a range of soil physical property measurements important for agricultural, environmental and turf grass majors in a manner that assists students to solve real world problems. 3. Ecosystem management modifications of soil physical heterogeneity: Recent journal articles and book publications. Course Evaluations: 1. Quizzes: Given at the beginning of selected class lectures; 15% Therefore be prepared for a possible quiz before each class lecture by reading the assigned reading, for each lecture, before each class lecture. 2. Exam 1; (Lectures 1-5 ) 25% 3. Laboratory Sessions, Reports and Problem Sets; 25% 4. Final Exam; (Lectures 6 – 12, lab sessions and reading assignments) 35% Lecture 1 1.0 Introduction 1.1 Historical 1.2 First soil science book 1.3 Civilization depends on the soil-plant- atmosphere continuum for survival 1.4 Soil is the foundation matrix of life 1.5 Concealment of roots 1.6 Course goals 1.7 Three general soil stresses to plant growth 1.8 Definition of Soil Physics 1.9 Soil-Plant-Atmosphere Continuum (SPAC) 1.4 Today, as throughout history, we ultimately depend upon the dynamic nature of the soil-plant root-atmosphere continuum (SPAC) for our survival. Ironic dilemma of SPAC is that 80% of what we know about plants is based upon the above ground portions of the plant. At least half of all photosynthetic carbon is used below ground, in the soil and by dark respiration. 1.5 Concealment of plant roots by the soil introduces an obvious complication into the SPAC studies of root and soil relationships. Furthermore, difficulties arise from the random and highly variable nature of the roots in soil profiles. One of the paradoxes of soil and the plant root system interrelationships is that the very environment which supports root growth often becomes too hostile, and actually inhibits normal root function. Unfavorable soil conditions restricting the performance of roots are a common reason why crop yields and plant quality are much lower than their potential maximum, based upon their genetic characteristics, incident solar radiation and thermal conditions permit. R.S. Russell, 1980 The Plant Root System – Their Function and Interaction with the Soil Millions 106/g Billions of cells 109/g soil 1015 cells per m3 80% of the reductions in plant productivity, for 8 different crops, resulted from physiochemical soil stresses. John Boyer, Science, 1982 Breman (2002) has identified annual yield losses, among most major cereal crops, exceed $10 billion due to drought. Breman also demonstrates accompanying land degradation, resulting from inadequate vegetative cover on doughty soils adversely affects 25% of the world's total land area and 19% of the world’s population. Reality is that the grim figure of 940 million people who experience daily hunger and/or starvation mandate extraordinary science that will bring releaf to the human race and environmental sustainability to soil, water and other natural resources. Long-term world population growth, 1750-2050. (Source: United Nations Population Division; “The World at Seven Billion”) What is our responsibility, as global citizens, to improve the world food supply and other plant life on this planet? Mr. Cullers produced 139 bu. soybeans per acre. Average soybean yield in Michigan is 40 bu/a. 8,340 pounds per acre (9341 kg/ha) Mr. Cullers also produced 346 bu (20,760 pounds) of corn grain per acre. 120 pods/plant Protein = 41% Irrigated with 0.2 to 0.3 inches/d July – September on soil with clay pan below root zone. Kip Cullers SW Missouri A B Roots of maize which recolonize previous soil macropores developed by maize roots of previous crops, develop many more disease lesions (arrows in B) than maize roots which occupy bulk soil (A) or recolonize root induced macropores (RIMs) developed by alfalfa species. Healthier roots of maize following other crops may be one of the major factors contributing to the positive contribution referred to as the rotation effect. Digital micro-camera, with lights for recording root numbers intersecting clear plastic minirhizotron tubes in soils. Depth: Kalamazoo loam KBS/LTER Alfalfa G ro w th D ea th - MPa Growth and death responses of ephemeral roots of maize in a Spinks sand (mixed, mesic Psammentic Hapludalf) soil during 32 days of a water deficit during the vegetative stage. Maximum root branching occurred until soil water potentials approached -60 kPa, when these tertiary branches died back to original parent roots accounting for the 1700 roots lost m-2 in the surface 50 cm depths. (From Smucker and Aiken, 1992). -60 kPa Water potential (- MPa) Growth and death responses of ephemeral roots of maize in a Spinks sand (mixed, mesic Psammentic Hapludalf) soil during 32 days of a water deficit during vegetative stage. Maximum root branching occurred until soil water potentials approached -60 kPa, when these tertiary branches died back to original parent roots accounting for the 1700 roots lost m-2. (From Smucker and Aiken, 1992). -60 kPa Excellent soil water contents cause roots to grow and absorb water and utrients. Dry soils kill plant roots! 2/3 of roots died Second goal: 2) Develop correct prognoses during your identification of specific problem areas encountered in the fields, lawns, golf courses, parks, grassland and forested areas. 1.7 Three general soil stresses to plant growth: 1) Biological stresses: Includes disease caused by a biological or causal organism. Types: a) Allelopathic: suppression of plants b) Competitive: weeds/intercropping c) Symbiotic: Rhizobium nodules 2) Chemical stresses: Shortage or imbalance of nutrients or toxic levels of some heavy metals or non-essential elements in any region of the soil. a) Crop yields are frequently limited by inadequate supplies of essential nutrients. b) Soil chemists have discovered ways of alleviating these chemical stresses, during the past 50 years, by using the proper balance of inorganic fertilizers, crop rotations with legumes, high- biomass cover crops, and organic amendments. 3) Physical stresses: gaseous, liquid or solid limitations to root growth and plant productivity. a) Causes are heavy machinery, frequent traffic and excessive tillage when soils are too wet. b) During the next 12 to 14 class periods and two laboratory exercises we will identify a portion of these physical stresses. Relationship between soil water film thickness and moisture tension or matric potential (-M) (Source: Physical Geography. net.) Within the soil system, the storage of water is influenced by several different forces. The strongest force is the molecular force of elements and compounds found on the surface of soil minerals. The water retained by this force is called hygroscopic water and it consists of the water held within 0.0002 millimeters of the surface of soil particles. The maximum limit of this water around a soil particle is known as the hygroscopic coefficient. Hygroscopic water is essentially non-mobile and can only be removed from the soil through excessive heating. Matric force holds soil water from 0.0002 to 0.06 millimeters from the surface of soil particles. This force is due to two processes: soil particle surface molecular attraction or adhesion of water molecules to mineral surfaces, and the cohesion that water molecules have to each other. Available water to plants Unavailable water to plants. General relationship between soil water characteristics and soil texture. Remember these are representative curves & individual soils will likely have values different from those shown. (Brady and Weil, 2004, p. 157) 1) Note that wilting coefficient increases as texture becomes finer. 2) Field capacity θv increases until as texture becomes finer until silt loams, then levels off. 3) Greatest plant-available H2O capacity (PAWC) occurs with medium- rather than fine-textured soils. 1.9 Soil-Plant-Atmosphere-Continuum (SPAC) 1.9.1 Soil is the weathered and fragmented outer layer of the earth’s mantel that has been modified by climate and cultivation. 1.9.2 Soil is a complex system with multiple components, each having multiple variables. Polyphasic, heterogeneous, particulate, disperse, porous 1) Polyphasic – solid, liquid, and gas 2) Heterogeneous – The soil has many inter- and intra-phasic properties that change with time and space. 0 0.3 0.6 0.9 1.2 1.5 0.10 0.20 0.30 0.40 Volumetric Water Content (cm3/cm3) x 100 S o il M a tr ic W a te r P o te n ti a l (- b a rs ) Soil water retention (characteristic) graph for a well-structured loam soil - 1 atmosphere - 1023 cm water - 760 mm Hg 3) Particulate – size, shape, chemical nature and composite texture 4) Disperse – the colloidal nature and interfacial activity gives rise to swelling, shrinking, aggregation, adsorption, hydration, ion exchange, etc. Ex.-- Area of up to 800 m2 g-1 of 2:1 clay 5) Porous – soil particle arrangements give rise to particles and pores that transmit or retain soil solutions, gases and thermal gradients. Hillel (2004), p. 375 Clearly, the major portion of the overall potential difference in the SPAC occurs between the leaves and the atmosphere. 1.9.5 Examples of dynamic SPAC: Water: Approximately 100 times more water is absorbed from the soil and transported to the atmosphere by plants than is retained by the plant during one season of growth. A corn plant contains approximately one liter of water at physiological maturity, while nearly 100 liters have transpired across the leaf surfaces during the growing season. Calculations: If each corn plant transpires 100 liters/season, and if there are 34,848 corn plants per acre, and we know there are 3.78 liters per gallon then, [100 x 34,848] / 3.78 = 921,905 gallons/acre/season Therefore, nearly a million gallons of water are required to produce an acre of corn each year! Calculation for next Wednesday’s class: If 280 mm of rainfall and supplemental irrigation were added to an acre of corn, would there be adequate water for the corn crop? 0 0.3 0.6 0.9 1.2 1.5 0.10 0.20 0.30 0.40 Volumetric Water Content (cm3/cm3) x 100 S o il M a tr ic W a te r P o te n ti a l (- b a rs ) Soil water retention graph for a well-structured loam soil - 1 atmosphere - 1023 cm water - 760 mm Hg Due to the smaller pore sizes & greater surface area, θv in the clayey soil is > the θv in the sandy soil. Hillel (2004), p. 115 S o il m a tr ic w a te r p o te n ti a l - b a rs 0 Saturated Plant-Available H2O (cont’d) As water infiltrates into the soil by moving across the soil surface, it proceeds into and through the soil profile by a process called internal drainage. Gravity (ψg ) influences most of this type of H2O flow. Then, as water flow ceases, the matric forces (ψm) retain this water at a soil water status often referred to as “field capacity” Effects of soil organic matter content on the field capacity and wilting percentage for a number of silt loam soils showing how PAWC can be increased. (Brady and Weil, 2004, p.158) 1.10. Water Use Efficiency (WUE) Lack of PAW to meet plant ET demands can lead to drought stress. This stress affects physiological processes: 1st, cell growth 2nd, wall synthesis & protein synthesis 3rd, stomatal opening & CO2 assimilation 4th, respiration 5th, proline & sugar accumulation One measure of drought stress on crops & plants is WUE, which can be defined as: WUE = dry matter produced (DM)/actual evapotranspiration (AET) WUE = seed yield (SY)/AET ex., tons DM/ac-in of H2O evapotranspired; lb or bu grain/ac-in of H2O 8-9 bushels of corn per acre inch of water lost by ET WUE (cont’d) WUE varies with climate, soil & crop factors, but between 200–800 kg H2O is used to produce 1 kg DM (or 200–800 lb H2O is used to produce 1 lb DM) Example WUE calculation (Scott, p. 347 & 349): assume 19.6” of seasonal AET to grow 8,450 lb/ac soybean DM WUE = 8,450 lb/ac / 19.6” = 431 lb/ac in. H2O since 1 ac-in = 27,150 gal & 1 gal = 8.34 lb, 1 ac in. ≈ 226,000 lb so, 226,000 lb H2O/431 lb DM = 524 lb H2O lost/lb DM produced