Lecture 4.pdf

Environmental Engineering and Science (HS103C) Credit: 2 Dr. JYOTI KAINTHOLA Why soil is important ? Soil and Soil Dynamics Soil is important because it Is a medium for plant growth Serves as a filter for water A habitat for living organisms Serves as a fi...

Environmental Engineering and Science (HS103C) Credit: 2 Dr. JYOTI KAINTHOLA Why soil is important ? Soil and Soil Dynamics Soil is important because it Is a medium for plant growth Serves as a filter for water A habitat for living organisms Serves as a filter for pollutants Factors that determine the formation of soil: Parent material- Climate Topography Organisms Time Soil as an Ecosystem  Soil consists of 50% mineral matter  Up to 5% organic matter Dead and living microorganisms Decaying material from plants and animals  The remainder is pore space taken up by air and water  Soil is teeming with bacteria, algae, fungi, and protists and provides habitat for earthworms, insects, mammals, reptiles, and amphibians.  Since soil is composed of interacting living and non-living matter, it is considered an ecosystem Soil forms slowly ▪ Parent material = the base geologic material of soil ▪ Lava, volcanic ash, rock, dunes ▪ Bedrock = solid rock comprising the Earth’s crust ▪ Weathering = processes that break large rock particles down into smaller ones ▪ Physical (mechanical) = wind and rain; no chemical changes in the parent material ▪ Chemical = parent material is chemically changed ▪ Biological = organisms produce soil ▪ Humus = spongy material formed by partial decomposition of organic matter; holds moisture A soil profile consists of horizons ▪ Horizon = each layer of soil ▪ Soil can have up to six horizons ▪ Soil profile = the cross-section of soil as a whole Degree of weathering and amount of organic matter decrease in lower horizons ▪ Leaching = process whereby dissolved particles move down through horizons and may end up in drinking water Some materials in drinking water are hazardous ▪ Topsoil = inorganic and organic material most nutritive for plants Vital for agriculture Soils differ in color, texture, structure, and pH ▪ Soil color indicates its composition and fertility ▪ Black or dark brown soil is rich in organic matter ▪ Soil texture is determined by the size of particles ▪ From smallest to largest: clay, silt, sand ▪ Loam = soil with an even mixture of the three ▪ Affects how easily air and water travel through the soil ▪ Influences how easy soil is to cultivate ▪ Soil pH affects a soil’s ability to support plant growth ▪ Soils that are too acidic or basic can kill plants ▪ pH influences the availability of nutrients for plants Damage to soil and land makes conservation vital ▪ Soil degradation = a decline in soil quality and productivity ▪ Primarily from deforestation, cropland agriculture, overgrazing ▪ Over the past 50 years, soil degradation has reduced potential food crop production by 13% ▪ Land degradation = a general deterioration of land, decreasing its productivity and biodiversity ▪ Erosion, nutrient depletion, water scarcity, salinization, waterlogging, chemical pollution Conserving Soil ▪ Feeding the world’s rising human population requires changing our diet or increasing agricultural production ▪ But land suitable for farming is running out ▪ Mismanaged agriculture turns grasslands into deserts, removes forests, diminishes biodiversity and encourages the growth of non-native species ▪ It also pollutes soil, air, and water with chemicals ▪ Fertile soil is blown and washed away ▪ We must improve the efficiency of food production while we decrease our impact on natural systems Erosion threatens ecosystems and agriculture ▪ Erosion = removal of material from one place to another by wind or water ▪ Deposition = arrival of eroded material at a new location ▪ Flowing water deposits nutrient-rich sediment in river valleys and deltas ▪ Floodplains are excellent for farming ▪ Erosion occurs faster than soil is formed ▪ It tends to remove topsoil—the most valuable layer for plant growth Erosion threatens ecosystems and agriculture ▪ Erosion can be hard to detect and measure ▪ Physical barriers to capture soil can prevent erosion ▪ Plants prevent soil loss by slowing wind and water flow ▪ Roots hold soil in place ▪ No-till agriculture leaves plant residue on fields ▪ Cover crops protect soil between crop plantings Desertification reduces productivity of arid lands ▪ Desertification = a form of land degradation with more than a 10% loss of productivity ▪ Caused primarily by wind and water erosion, but also by: ▪ Deforestation, soil compaction, and overgrazing ▪ Drought, salinization, water depletion ▪ Climate change ▪ Arid and semiarid lands (drylands) are most prone to desertification ▪ Cover about 40% of the Earth’s surface Remedies?? Farmers protect soil in many ways ▪ Crop rotation = growing different crops from one year to the next ▪ Returns nutrients to soil ▪ Prevents erosion, reduces pests ▪ Like crop rotation, no-till farmers may alternate wheat or corn with nitrogen-fixing soybeans ▪ Contour farming = ploughing furrows sideways across a hillside perpendicular to its slope ▪ Sides of furrows trap water and prevent erosion ▪ Terracing = cutting level platforms into steep hillsides Farmers protect soil in many ways ▪ Intercropping = planting different crops in alternating bands or mixed arrangements ▪ Increases ground cover, preventing erosion ▪ Decreases pests and disease ▪ Replenishes soil ▪ Shelterbelts (windbreaks) = rows of trees planted along edges of fields to slow the wind ▪ Can be combined with intercropping ▪ Conservation tillage = strategies that reduce the amount of tilling relative to conventional farming ▪ Leaves at least 30% of crop residues in the field ▪ No-till farming disturbs the soil even less THANK YOU