Soil Management: the basis of sustainable agriculture FAB-465 Lecture 11 Lecture Outline Soil Formation Soil Structure/Texture Indicators of Soil Health or Fertility Soil Conservation Practices 1
Soil Formation Dynamic Process carried out over millions of years Mainly brought about by weathering of parent material (both chemical and physical action) Continental shift Erosion Transport Weather Plants and animals in soil Soil Formation Complex process involving formation and decay of organic matter Pedogenesis processes involved in the formation of soil A number of different factors are involved Parent material Climate Soil organisms and vegetation Topography Human activities 2
Layers of Soil Soil is usually a combination of sand, silt and clay Assembly of particles gives rise to aggregates Patterns of aggregation vary, resulting in different soil structure Soil Profiles Plough Layer: 20-30 cm thick, organic matter and live roots, dark colour Deep Plough Layer: Less organic matter and live roots, lighter colour, often greyish Subsoil layer: hardly any organic matter, not very important for plant growth Parent rock layer: Bedrock or parent material 3
Soil Structure Variation is mainly based on the permeability of water ftp.fao.org Soil Structure Soil structure mostly described in terms of the following properties of soil aggregates Grade (degree of aggregation) Class (average size) Types of aggregates (form) 4
Soil Texture Size of particles that make up soil The Size of Sand, Silt and Clay Name Particle Diameter Clay below 0.002 millimeters Silt 0.002 to 0.05 millimeters Very fine sand Fine sand Medium sand Coarse sand Very coarse sand Gravel Rock 0.05 to 0.10 millimeters 0.10 to 0.25 millimeters 0.25 to 0.5 millimeters 0.5 to 1.0 millimeters 1.0 to 2.0 millimeters 2.0 to 75.0 millimeters greater than 75.0 millimeters (~2") Soil Texture Triangle 5
Indicators of Soil Health/Fertility Biological Chemical Physical Some common examples of soil stressors USDA Natural Resources Conservation Services 6
Physical Indicators Aggregate Stability Available Water Capacity Bulk Density Infiltration Soil Crusts Soil Structure and Macropores Physical Indicators Aggregate Stability Ability of soil aggregates to resist disintegration Creation of pore space for water infiltration Inherent factors Predominant type & amount of clay Adsorbed cations (Ca, N, Iron oxide content) Stability enhanced with Ca, Mg, Fe, Al -> formation of organic matter Dynamic Organic Matter and Biological Activity 7
Available Water Capacity Maximum amount of plant available water a soil can provide Soil s ability to retain water and make it available for plants Saturation Field capacity Permanent Wilting Point Physical Indicators Bulk Density Physical Indicators Measure of soil compaction Structural support, water and solute movement, soil aeration Infiltration Downward entry of water into the soil (Inches per hour) Dependant on soil texture 8
Physical Indicators Soil Crusts Thin, dense, somewhat continuous layers of nonaggregated soil particles on surface of tilled and exposed soils Influenced by soil texture, organic matter, Na content Indicates poor infiltration, reduced air exchange Increased Na content increased soil dispersion Restriction of seedling emergence Soil Crusts www.soilquality.org 9
Chemical Indicators Soil Electrical Conductivity Soil ph Soil Nitrate Chemical Indicators Soil ph Ideal ph for most crops 6.5-7 Sources of H+ ions include artificial fertilizers Carbon dioxide released from organic matter decomposition Rain water, acid rain Liming, application of limestone to the field to increase ph Direct and indirect impact on plant growth 10
Chemical Indicators Soil Electrical Conductivity The ability of soil water to carry electrical current Cations and anions from salts dissolved in water Saline soils have high electrical conductivity Soil Nitrate Soil texture and nitrate retention Potential to decrease soil ph (acidification) Dependent upon the N fertilizers applied Biological Indicators Earthworms Particulate Organic Matter Potentially Mineralizable Nitrogen (PMN) Soil Enzymes Soil Respiration Total Organic Carbon 11
Biological Indicators Earthworms Burrow narrow channels Feed on a mixture of soil and plant residues The depth of burrowing depends on the type of earthworms Excreted material released back into the soil (N, P, K and Ca) and microbes Fresh cast is the site of excess microbial and nutrient cycling activity Porosity, root development, aggregate stability, soil structure Soil Enzymes Biological Indicators Decomposition of plant residues, increase the rate of release of plant-available nutrients Particulate Organic Matter (POM All soil organic matter particles between 2mm and 0.053mm in size Biologically and chemically active Part of the easily decomposable pool of SOM 12
Phosphate Solubilization by fungus on Pikovskaya medium Soil Respiration Biological Indicators The amount of carbon dioxide produced by the soil as a result of different soil activities Decomposition of organic matter, Affected by temperature, moisture, aeration etc 13
(i) (ii) (iii) (iv) (v) Recommendations for Effective Soil Management liberal use of crop residues, animal dung and other biosolids, minimal disturbance of soil surface to provide a continuous cover of a plant canopy or residue mulch, Judicious use of sub-soil fertigation techniques to maintain adequate level of nutrient and water supply required for optimal growth, an adequate level of microbial activity in the rhizosphere for organic matter turnover and elemental cycling, and use of complex cropping/farming systems which strengthen nutrient cycling and enhance use efficiency of input. 14