02 Major components of soil of soil science.pptx.pdf
- 1. Soil components Soil Components: Soils consist of four major components: (1) mineral (or inorganic), (2) organic, (3) water, and (4) air. The relative proportions of these four soil components vary with soil type and climatic conditions.
- 2. Review the approximate proportions (by volume) of the four soil components in a mineral soil under optimum conditions for plant growth.
- 3. Mineral particles are inorganic materials derived from rocks and minerals. They are extremely variable in size and composition. Minerals Primary Minerals Secondary Minerals 1. Mineral Components
- 4. Primary minerals – has the same chemical composition as the primary rock • Primary minerals are formed at high temperature and pressure, under reducing conditions without free oxygen. • These minerals are mainly present in soils as sand and silt particles. • They are not crystallized and deposed from molten lava.
- 5. Secondary minerals – has different composition from parent rock • Secondary minerals are formed at low temperature and pressure through oxidation. • They are the weathering product of primary minerals, either through alteration of their structure or through re-precipitation. • Secondary minerals are usually present in soil as clay particles.
- 6. Soil mineral particles Size Characteristics Sand 2.0 mm-0.05mm Sand, visible to naked eye, no plasticity, stickiness, shrinkage or swelling capacity. Quartz dominant Silt 0.05mm -0.002mm Not visible to the naked eye. Increases water holding capacity Some plasticity and stickiness, capability of adsorption Clay ˂ 0.002mm High water holding capacity, Many small pores, Hold nutrients High plasticity, stickiness and shrinkage, high adsorptive Include ………………More
- 7. 2. Organic Matter Soil organic matter (SOM) can be of plant, animal, or microbial origin and may be relatively fresh or highly decomposed and transformed. In this course, terms soil organic matter and humus are considered synonyms. Living components Non living components waste macro O. M. Dissolved O. M. Humus (humic acid) Phytomass – living plants Micro biomass- micro organism Faunal biomass- worms insects Organic Matter
- 8. • Reservoir of metabolic energy • Source of macro-nutrients • Ecosystem resilience • Stimulation and inhibition of enzyme activities of plant and microbial growth. • Enhance exchange capacity • Enhance buffering capacity
- 10. (OM) Important soil component because it: • holds soil particles together and stabilizes the soil, thus reducing the risk of erosion; • b) aids crop growth by improving the soil's ability to store and transmit air and water; • c) stores and supplies many nutrients needed for the growth of plants and soil organisms; • d) prevents or minimizes soil compaction; • e) retains carbon from the atmosphere; • f) reduces the negative environmental effects of pesticides, heavy metals, and many other pollutants.
- 11. 3. Water • Water is the major transport agent for fluxes within and between terrestrial ecosystems. • It is a prerequisite for all active life, and participates in geochemical cycles by weathering geological substrates, by leaching materials to groundwater and by moving ions and particles through the soil profile. • Soil water is part of the global hydrological cycle, which shows how water that falls as precipitation returns to the atmosphere through transpiration and evaporation. On a local scale, how well the soil stores water is of great importance to crop production and the vitality of the land.
- 12. Water Content: Comparisons of a soil under saturated, field capacity, and wilting point, and hygroscopic point conditions
- 13. Hydrological cycle and soil water contained
- 14. Necessity of soil water • Optimum water supply essential for plant growth • It helps in seed germination • Need for evapotranspiration (for large trees) • Dissolve the nutrients and make them available to plants • It effect soil structure and other chemical, physical and biological attributes • Destroy soil temperature (excess temp.)
- 15. 4. Air • Soil pores, the voids between minerals, organic matter, and living organisms, are filled with air or water. There is a dynamic equilibrium between water and air content within a soil. When water enters the soil, it displaces air from some of the pores. • Composition of soil air • The composition of soil air is different from that of the atmosphere because it cannot readily mix with air above the soil. • The metabolic activity of plant roots, microbes and soil fauna all affect the composition of soil air. • For example, the concentration of carbon dioxide (CO2 ) in soil (between 0.3 and 3%) is often several hundred times higher than the 0.03% found in the atmosphere.
- 16. • In extreme cases oxygen can be as low as 5-10%, compared to 20% in the atmosphere. • Soil air has a higher moisture content than the atmosphere, with relative humidity approaching 100% under optimum conditions. (humidity is not as variable in soil as it is in the atmosphere). • The amount and composition of air in soil are dynamic and to a large degree are determined by water content and activity of soil organisms.
- 17. Measurement of soil respiration
- 18. Movement of gasses within soil • The exchange of gases between the atmosphere and soil is facilitated by two mechanisms: • 1) Mass flow (convection) of air - the moving force is a gradient of total gas pressure, and it results in the entire mass of air streaming from a zone of higher pressure to one of lower pressure. Mass flow of air is much less important than diffusion, except perhaps in layers at or very near the soil surface. • 2) Diffusion - moving force is gradient of partial pressure of any constituent member of air to migrate from a zone of higher to lower pressure, even while air as a whole may remain stationary. In other words, through diffusion each gas moves in a direction determined by its own partial pressure.
- 19. • Thanks