BESC 201 10 23 2013 Lecture 22 Outline of Last Lecture I The Changing Face of Agriculture Outline of Current Lecture II Maintaining Healthy Soils III Watering and Fertilizing Crops IV Controlling Pests Current Lecture 10 23 2013 Maintaining Healthy Soils Soil Degradation a process in which soils have deteriorated in quality and declined in productivity Erosion can degrade ecosystems and agriculture Erosion the removal of material from one place and its transport toward another by the action of wind or water Deposition occurs when eroded material arrives at a new location and is deposited Steeper slopes greater precipitation intensities and sparser vegetation cover all lead to greater water erosion People have made land more vulnerable to erosion through three widespread practices 1 Overcultivating fields through poor planning or excessive tilling 2 Overgrazing rangeland with more livestock than the land can support 3 Clearing forests on steep slopes or with large clear cuts Desertification reduces productivity of arid lands Dry Lands arid and semi arid environments Desertification a form of land degradation in which more than 10 of productivity is lost Desertification could worsen as climate change alters rainfall patterns The Dust Bowl prompted the United States to fight erosion A drought exacerbated the ongoing human impacts and the region s strong winds began to erode millions of tons of topsoil Dust Bowl the most affected region in the southern Great Plains now used for the historical event itself These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute The U S Congress passed the Soil Conservation Act of 1935 establishing the Soil Conservation Service SCS Sustainable agriculture begins with soil management Crop Rotation farmers alternate the type of crop grown in a given field from one season or year to the next Rotating crops can return nutrients to the soil break cycles of disease associated with continuous cropping ad minimize the erosion that can come from letting fields lie fallow Contour Farming plowing furrows sideways across a hillside perpendicular to its slope and following the natural contours of the land The side of each furrow acts as a small dam that slows runoff and captures eroding soil most effective on gradually sloping land with crops that grow well in rows Terracing transforms slopes into series of steps like a staircase enabling farmers to cultivate hilly land Intercropping planting different types of crops in alternating bands or other spatially mixed arrangements Shelterbelts rows of trees or other tall plants that are planted along the edges of fields to slow the wind Conservation Tillage an array of approaches that reduce the amount of tilling relative to conventional farming Critics say that no till farming requires substantial use of chemical herbicides and synthetic fertilizer Proponents say that farmers have begun relying more heavily on green manures dead plants as fertilizers Grazing practices can contribute to soil degradation Overgrazing when too many livestock eat too much of the plant cover In a positive feedback cycle soil erosion makes it difficult for vegetation to regrow which gives rise to more erosion Agriculture subsidies affect soil degradation Subsidies can encourage people to cultivate land that would otherwise not be farmed to produce more food than is needed driving down prices for other producers and to practice methods that further degrade the land A number of U S and international programs promote soil conservation Conservation Reserve Program pays farmers to stop cultivating highly erodible cropland and instead place it in conservation reserves with grasses and trees Watering and Fertilizing Crops Irrigation boosts productivity but can damage soil Irrigation the artificial provision of water to support agriculture Waterlogging when over irrigation causes the water table to rise to the point that water drowns plant roots depriving them of access to gases and essentially suffocating them Salinization the buildup of salts in surface soil layers Sustainable approaches to irrigation maximize efficiency One of the most effective ways to reduce water use is agriculture is to better match crops and climate New drip irrigation systems that deliver water directly to plant roots can increase efficiencies Fertilizers boost crop yields but can be overapplied Fertilizer substances that contain essential nutrients Inorganic Fertilizers mined or synthetically manufactured mineral supplements Organic Fertilizers consist of the remains or wastes of organisms Compost a mixture produced when decomposers break down organic matter Inorganic fertilizers are generally more susceptible to leaching than organic fertilizers and more readily contaminate groundwater supplies Sustainable fertilizer use involves monitoring and targeting nutrients Farmers using drip irrigation systems can add fertilizer to irrigation water thereby releasing it only above plant roots No till or conservation tillage systems often inject fertilizer along with seeds concentrating it near the developing plant Controlling Pests Pest any organism that damages crops that are valuable to us Weed any plant that competes with our crops We have developed thousands of chemical pesticides Pesticides chemicals to kill insects insecticides plants herbicides and fungi fungicides Pests evolve resistance to pesticides A small fraction of organisms may by chance already have genes that enable them to metabolize and detoxify a pesticide If an insect that is genetically resistant to an insecticide survives and mates with other resistant individuals the genes for pesticide resistance will be passed to their offspring Industrial chemists are caught up in an evolutionary arms race with the pests they battle racing to increase or retarget the toxicity of their chemicals while the armies of pests evolve everstronger resistance o Nicknamed pesticide treadmill Biological control pits one organism against another Biological Control battling pests and weeds wit organisms that eat or infect them Biocontrol organisms are sometimes more difficult to manage than chemical controls because they cannot be turned off once they are initiated Integrated pest management combines varied approaches to pest control Integrated Pest Management IPM incorporates numerous techniques including biocontrol use of chemicals when