Soil and Agriculture - Environmental Sciences - Lecture Slides, Slides of Environmental Science

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Soil and Agriculture Chapter 9 Environmental Science docsity.com Soil: the foundation for agriculture • Land devoted to agriculture covers 38% of Earth’s land surface • Agriculture = practice of raising crops and livestock for human use and consumption • Cropland = land used to raise plants for human use • Rangeland or pasture = land used for grazing livestock • Soil = a complex plant-supporting system – is a renewable resource docsity.com Industrialized agriculture is a recent phenomenon • Industrialized agriculture = using large-scale mechanization and fossil fuels to boost yields – uses pesticides, irrigation and fertilizers – Monocultures = uniform planting of a single crop • Green revolution = introduced new technology, crop varieties and farming practices to developing countries – increased yields – created new problems and worsened old ones docsity.com Soil as a system • Soil consists of mineral matter, organic matter, air, and water – dead and living microorganisms, and decaying material – bacteria, algae, earthworms, insects, mammals, amphibians, and reptiles 6 Since soil is composed of interacting living and nonliving matter, it is considered an ecosystem docsity.com Soil formation is slow and complex • Parent material = the base geologic material of soil – lava, volcanic ash, rock, dunes – Bedrock = the continuous mass of solid rock comprising the Earth’s crust • Weathering = the physical, chemical, or biological processes that break down rocks to form soil – Physical (mechanical) = wind and rain, • no chemical changes in the parent material – Chemical = substances chemically interact with parent material – Biological = organisms break down parent material 7 docsity.com Soils are characterized in many ways • Soils are classified based on color, texture, structure, and pH – Soil color = indicates its composition and fertility • black or dark brown = rich in organic matter • pale gray or white = indicates leaching – Soil texture = determined by the size of particles • from smallest to largest = clay, silt, sand – Loam = soil with an even mixture of the three • influences how easy it is to cultivate and let air and water travel through the soil docsity.com Soil structure and pH – Soil structure = a measure of soil’s “clumpiness” • large clumps can discourage plant roots • repeated tilling compacts soil, reduces water-absorbing capabilities • Plowpan = a hard layer resulting from repeated plowing…resists water infiltration and root penetration – Soil pH = influences a soil’s ability to support plant growth • soils that are too acidic or basic can kill plants docsity.com Cation exchange is vital for plant growth • Cation exchange = process that allows plants to gain nutrients – negatively charged soils hold cations (positively charged ions) of calcium, magnesium, and potassium • Cation exchange capacity = a soil’s ability to hold cations – preventing them from leaching – increasing their availability to plants – a useful measure of soil fertility docsity.com Various types of soil erosion Splash Sheet Rill Gully docsity.com Desertification • Desertification = a loss of more than 10% productivity • erosion • soil compaction • forest removal • overgrazing • salinization • climate change • depletion of water sources • Most likely areas = arid and semiarid 16 Signs of desertification in fields located on the outskirts of Ségou, Mali docsity.com The Dust Bowl • In the late 19th and early 20th centuries…settlers arrived in Oklahoma, Texas, Kansas, New Mexico and Colorado – grew wheat, grazed cattle • removed vegetation • A drought in the 1930s made conditions worse docsity.com Protecting soil: crop rotation and contour farming • Crop Rotation = alternating the crops grown from one season or year to the next – Returns nutrient to soil – Prevents erosion, reduces pests – wheat or corn and soybeans • Contour Farming = plowing furrows sideways across a hillside, perpendicular to its slope – prevent rills and gullies 20 docsity.com Protecting soil: terracing and intercropping • Terracing = level platforms are cut into steep hillsides – a “staircase” to contain water • Intercropping = planting different types of crops in alternating bands – increases ground cover – Replenishes soil docsity.com Protecting soil: shelterbelts and reduced tillage • Shelterbelts or Windbreaks = rows of trees or tall, perennial plants…planted along edges of fields to slow the wind • Reduced Tillage = furrows are cut in the soil, a seed is dropped in and the furrow is closed – No-till farming • disturbs the soil even less 22 docsity.com Salinization prevention • Do not plant water- guzzling crops in sensitive areas • Irrigate with low-salt water • Irrigate efficiently… supplying only water that the crop requires – drip irrigation targets water directly to plants 25 docsity.com Fertilizers boost yields but cause problems • Fertilizer = substances that contain essential nutrients • Inorganic fertilizers = mined or synthetically manufactured mineral supplements • Organic fertilizers = the remains or wastes of organisms – manure, crop residues, fresh vegetation – Compost = produced when decomposers break down organic matter Applying synthetic fertilizer, vs. Planting rye, a “green manure” docsity.com Over-application of Fertilizer • Over applying fertilizer: – ruins the soil – severely pollutes several areas • runoff causes eutrophication in nearby water systems • nitrates leach through soil and contaminate groundwater 27 docsity.com