Soil and Agriculture Chapter 9

Soil: The Foundation for Sustainable Agriculture Agriculture – raising of crops and livestock for human use Agriculture can increase need for irrigation and fertilizer Cropland – land used to raise crops Rangeland or pasture – land used for grazing 38% of Earth’s land used for agriculture Soil – combination of mineral, rock, water, air, microorganisms, gases, and decaying organic matter (humus) that supports plant growth Soil is a renewable resource that could be depleted

Sustainable agriculture - agriculture practices that can be employed far into the future without compromising the resource Healthy soil is necessary for: Productive agriculture Soil retention Water retention Many living things depends on healthy soil in some way for their food

Agricultural Revolution 10,000 years ago agriculture arose independently in several areas: China Middle east Americas Africa Societies switched from hunter-gather to fixed Fixed societies grew larger leading to first cities requiring increased food production

Industrial Agriculture Dominates Today Traditional agriculture – agriculture powered by human and animal Uses simple hand tools and machines Subsistence agriculture – agriculture that only produces enough food for the family that grows it Polyculture – having several crops planted in one field Market economies allow farmers to sell their products

Industrialized agriculture – agriculture relying on mechanization and fossil fuels to boost yields Monoculture - planting of a single crop Green Revolution - 1950s introduced new technologies, crop varieties, and farming practices to developing nations Increased food production, decreased starvation Soil degradation increased

Soil as a System Living organisms Decaying organic matter Soil is: 50% mineral and rock Up to 5% organic matter Living organisms Bacteria, algae, protists, fungi, earthworms, insects, mammals, reptiles, and amphibians Decaying organic matter Remaining space is air and water Soil is made of biotic and abiotic factors, therefore is considered an ecosystem

Soil Forms Slowly: Parent material – the geologic base of soil Lava, volcanic ash, rock, dunes Bedrock - solid rock that makes up Earth’s crust Weathering is a key process in the rock and mineral makeup of soil formation is also influenced by Climate – soils form faster is warmer more humid climates than in cooler drier climates Organisms – add organic matter Topography - soils is thicker at the base of a slope that on the side of a slope, amount of exposure to sunlight, wind, and precipitation all affect soil formation

Parent material – determines that type of rock and mineral soil contains Time – soils can take a few years to a few thousand years to form

Soil Profiles and Horizons: Soil profile – a vertical column of soil horizons Soil horizon – the individual layers within a soil profile Can be up to six horizons in a profile Leaching – as rain infiltrates soil, particles are moved through horizons Particles may become part of drinking water If particles are toxic, water could become inconsumable Topsoil – the horizons most beneficial to plants Usually the O and A horizons

Soils Differ: Soil color indicates composition and productiveness The darker the more organic matter it has meaning soil is nutrient rich Pale soil shows leaching often meaning soil is nutrient poor Texture is determined by particle size From smallest to largest Clay Silt Sand

Loam – soil with good mix of silt, clay, and sand Allows water and air to move freely through soil without allowing it to move to quickly Loam soils are easy to cultivate Structure refers to its “clumpiness” Medium clumpiness is good Over tilling or repeated tilling compacts soils, preventing water movement pH affects soil ability to support plant growth To acidic or basic will kill plants

Cation Exchange: Cation exchange is vital for plant growth Cation exchange - a process allowing plants to gain needed nutrients Negatively charged soil holds cations of Ca, Mg, and K Roots donate H to soil in exchange for these nutrients Cation exchange capacity – soil’s ability to hold cations Cations that don’t leach from upper horizons become available to plants Soils with fine texture or rich in organic matter have higher cation exchange capacity

Soil Conservation Soil Conservation is Vital: Increased population requires increased food production Arable land (suitable for farming) is being depleted and mismanagement is causing Deforestation Diminishing biodiversity Encouraging growth of non-native species Soil, air, and water pollution Loss of topsoil from wind and water runoff

Soil degradation – decline in quality and productivity of soil Caused mainly by deforestation, crop agriculture, and overgrazing Land degradation – overall decline of land’s productivity and biodiversity

Wind and flowing water generate erosion Vegetation holds soil in place No-till agriculture reduces exposure Cover crops protects soil between seasonal plantings Desertification – land degradation with more than a 10% productivity loss Caused by, deforestation, overgrazing, drought, and climate change Arid regions are prone more Arid regions cover nearly 40% of Earth’s surface

The Dust Bowl: During the 1930s in the southern Great Plains, the Dust Bowl formed as a response to prolonged drought, over cultivation, and overgrazing Tons of valuable topsoil were blown away leading to the formation of the Soil Conservation Service in 1935. The service developed conservation plans through the creation of conservation districts that dealt with farms at the county level 1994 the service was renamed the Natural Resources Conservation Services (NRCS) Expanded to include water quality and pollution control

Farming to Protect Soil: Crop rotation – changing what’s grown from year to year Contour farming – planting crops perpendicular to the slope of the land to provide a barrier to erosion Terracing – cutting platforms into hillsides to create flat areas like stair steps Intercropping – alternating rows of crops creating a mixed arrangement Shelterbelts (windbreaks) – rows of tress planted along the perimeter of a field to provide wind protection

Conservation tilling – reduces the amount of tilling needed No-till reduced erosion even more Better soil quality, more humus, carbon storage Less labor, less machinery wear, less fossil fuel used 40% of U.S. farmland uses conservation tillage

Overgrazing - too many animals eating too much plant cover

Watering and Fertilizing Crops Irrigation: Irrigation - providing water to support agriculture 70% of all freshwater is used in agriculture Used in regions normally not arable or for water intensive crops like rice and cotton Matching crops to climate can reduce need for irrigation Traditional irrigational causes up to 45% of water evaporate, drip irrigation puts more water to plants up to 90%

Salinization – the buildup of salts in soils surface layers Easier to prevent than fix Caused by continual irrigation, evaporation leaves salt behind Plant salt tolerant plants Flush soil with low salt water Let soil rest and let rainfall flush soil Waterlogging – over-irrigating until gas exchange in plant roots is prohibited Can lead to crop loss

Fertilizers Soil can be remediated by adding fertilizers Fertilizers – substances that contain essential nutrients N, Ph, K which limit plant growth if not proper amounts Organic fertilizers – the wastes or remains of living things Manure, compost, crop leftovers Compost - mixture of organic matter broken down by decomposers

The Green Revolution of the 19470s saw a rise in food production with: Genetically altered crops Improved pesticides Improved mechanization Inorganic fertilizers – mineral supplements that are mined or manufactured Increase soil compaction Decrease soils capacity to hold water Runoff can create dead zones Nitrate and phosphate build in drinking water can cause cancer and blue-baby syndrome Are cheap, easy to transport, and greatly increase food production

Agricultural Policy Government Policies and Agriculture: Policy has encouraged production Recent policy tries to lessen environmental impact Markets should discourage land degradation Governments spend billions on subsidizes, some are unsustainable Water intensive crops in arid regions Agriculture in areas where land degrades easily

Wetlands: Wetlands – marshes, swamps, bogs, and river floodplains More than 50% have been drained for agriculture in US US policy encouraged draining Swamp Lands Acts (1849, 1860, 1950) drained/converted wetlands to for flood and malaria control Wetlands now considered vital Wetlands Reserve Program – payment encourages landowners to restore, protect, and enhance wetlands

Programs Promoting Soil Conservation: 2008 “farm bill” funded 15 programs providing subsidies for farmers adopting soil conservation plans 1985 Conservation Reserve Program – farmers are paid to out easily eroded land into reserve, meaning it’s not used Income for farmers Money spent saves topsoil Better water quality Wildlife habitat

2012 farm bill never voted on, leaving future conservation programs in limbo Food and Agriculture Organization (FAO) is the UN main agriculture program Supports innovation in resource management and sustainable agriculture in Asia China and India both part of Asia Communities educate and encourage soil conservation and secure the food supply