erosion feedlots fertilizer food security genetic engineering genetically modified (GM) organisms green revolution gully erosion horizon humus industrialized agriculture inorganic fertilizers integrated pest management (IPM) irrigation leaching low input agriculture monoculture no-till agriculture O horizon organic agriculture organic fertilizers overgrazing parent material pesticides pollination precautionary principle R horizon rangelands rill erosion salinization seed banks sheet erosion shelterbelts soil soil profile splash erosion strip cropping sustainable agriculture terracing topsoil Key Words A horizon agriculture aquaculture B horizon bedrock biocontrol biological control biotechnology C horizon conservation tillage contour farming conventional irrigation crop rotation croplands deposition desertification drip irrigation Dust Bowl E horizon traditional agriculture transgenic waterlogged weathering
Objectives • Soil science fundamentals • Soil erosion and degradation • Soil conservation policies • Pest management and pollination • Genetically modified food and preserving crop diversity • Feedlot agriculture and Aquaculture • Organic agriculture
Central Case: No-Till Agriculture in Brazil • Southern Brazil’s farmers were suffering falling yields, erosion, and pollution from agrichemicals. • They turned to no-till farming, which bypasses plowing. • Erosion was reduced, soils were enhanced, and yields rose greatly. No-till methods are spreading worldwide.
Agriculture today We have converted 38% of Earth’s surface for agriculture, the practice of cultivating soil, producing crops, and raising livestock for human use and consumption. Croplands (for growing plant crops) and rangelands (for grazing animal livestock) depend on healthy soil.
Natural Capital Croplands Croplands Ecological Services Economic Services Ecological Services Economic Services • Help maintain water flow and • soil infiltration • Provide partial erosion protection • Can build soil organic matter • Store atmospheric carbon • Provide wildlife habitat for some • species • Food crops • Fiber crops • Crop genetic • resources • Jobs • Help maintain water flow and soil infiltration • Provide partial erosion protection • Can build soil organic matter • Store atmospheric carbon • Provide wildlife habitat for some species • Food crops • Fiber crops • Crop genetic resources • Jobs
Soil as a system • Parent material, such as bedrock, is weathered to begin process of soil formation. • Parent material = the base geological material in a location • Bedrock = the continuous mass of solid rock that makes up Earth’s crust • Weathering = processes that break down rocks
World soil conditions • Soils are becoming degraded in many regions. Figure 8.1a
Soil degradation by continent • Europe’s land is most degraded because of its long history of intensive agriculture. • But Asia’s and Africa’s soils are fast becoming degraded. Figure 8.1b
Causes of soil degradation • Most soil degradation is caused by: • • livestock overgrazing • • deforestation • • cropland agriculture. Figure 8.2
Components of soil • Soil is a complex mixture of organic and inorganic components and living organisms.
Humus • Dark, crumbly mass of undifferentiated material made up of complex organic compounds • Soils with high humus content • hold moisture better and • are more productive for plant life.
Soil profile • Consists of layers called horizons. • Simplest: • A = topsoil • B = subsoil • C = parent material • But most have O, A, E, B, C, and R Figure 8.8
Soil profile • O Horizon: Organic or litter layer • A Horizon: Topsoil. Mostly inorganic minerals with some organic material and humus mixed in. Crucial for plant growth • E Horizon: Eluviation horizon; loss of minerals by leaching, a process whereby solid materials are dissolved and transported away • B Horizon: Subsoil. Zone of accumulation or deposition of leached minerals and organic acids from above • C Horizon: Slightly altered parent material • R Horizon: Bedrock
Soil characterization • Soil can be characterized by color and several other traits: • Texture (percentage sand, silt, clay) • Structure • Porosity • Cation exchange capacity • pH • Parent Material • Infiltration rate • Nutrient concentrations • Best for plant growth is loam, an even mix of sand, silt and clay.
Erosion and deposition • Erosion = removal of material from one place and its transport elsewhere • by wind • or water • Deposition = arrival of eroded material at a new location • These processes are natural, and can build up fertile soil. • But where artificially sped up, they are a big problem for farming.
Erosion and Deposition • Sand dunes around Moses Lake are all that are left of the wind erosion in that area. The smaller particles, silt and clay were blown eastward toward the Palouse. The deposition of the silt and clay particles led to the formation of the Palouse Hills. The Palouse Hills are a wind/water erosional surface.
Erosion • Commonly caused by: • • Overcultivating, too much plowing, poor planning • • Overgrazing rangeland with livestock • • Deforestation, especially on slopes
Types of soil erosion Splash erosion Rill erosion Gully erosion Sheet erosion Figure 8.11
Erosion: A global problem • Over 19 billion ha (47 billion acres) suffer from erosion or other soil degradation. • Mississippi River…to thin to plow to thick to drink (Sam Clemens)
Desertification • A loss of more than 10% productivity due to: • • Erosion • • Soil compaction • • Forest removal • • Overgrazing • • Drought • • Salinization • • Climate change • • Depletion of water resources • • etc. When severe, there is expansion of desert areas, or creation of new ones, e.g., the Middle East, formerly, “Fertile Crescent”.
The Dust Bowl • Drought and degraded farmland produced the 1930s Dust Bowl. • Storms brought dust from the U.S. Great Plains all the way to New York and Washington, and wrecked many lives. Figure 8.14
Kansas Colorado Dust Bowl Oklahoma New Mexico Texas MEXICO
Consequences Causes Overgrazing Deforestation Erosion Salinization Soil compaction Natural climate change Worsening drought Famine Economic losses Lower living standards Environmental refugees
Soil conservation • As a result of the Dust Bowl, • the U.S. Soil Conservation Act of 1935 and • the Soil Conservation Service (SCS) were created. • SCS: Local agents in conservation districts worked with farmers to disseminate scientific knowledge and help them conserve their soil.
Preventing soil degradation • Several farming strategies to prevent soil degradation: • • Crop rotation • • Contour farming • • Intercropping • • Terracing • • Shelterbelts • • Conservation tillage
Crop rotation • Alternating the crop planted (e.g., between corn and soybeans) can restore nutrients to soil and fight pests and disease. Figure 8.16a
Contour farming • Planting along contour lines of slopes helps reduce erosion on hillsides. Figure 8.16b
Intercropping • Mixing crops such as in strip cropping can provide nutrients and reduce erosion. Figure 8.16c
Terracing • Cutting stairsteps or terraces is the only way to farm extremely steep hillsides without causing massive erosion. It is labor-intensive to create, but has been a mainstay for centuries in the Himalayas and the Andes. Figure 8.16d
Shelterbelts • Rows of fast-growing trees around crop plantings provide windbreaks, reducing erosion by wind. Figure 8.16e
Conservation tillage • No-till and reduced-tillage farming leaves old crop residue on the ground instead of plowing it into soil. This covers the soil, keeping it in place. • Here, corn grows up out of a “cover crop.” Figure 8.16f
Conservation tillage • Conservation tillage is not a panacea for all crops everywhere. • It often requires more chemical herbicides (because weeds are not plowed under). • It often requires more fertilizer (because other plants compete with crops for nutrients). • But legume cover crops can keep weeds at bay while nourishing soil, and green manures can be used as organic fertilizers.
Trade-Offs Conservation Tillage Disadvantages Advantages Can increase herbicide use for some crops Leaves stalks that can harbor crop pests and fungal diseases and increase pesticide use Requires investment in expensive equipment Reduces erosion Saves fuel Cuts costs Holds more soil water Reduces soil compaction Allows several crops per season Does not reduce crop yields Reduces CO2 release from soil
Irrigation • The artificial provision of water to support agriculture • 70% of all freshwater used by humans is used for irrigation. • Irrigated land globally covers more area than all of Mexico and Central America combined. • Irrigation has boosted productivity in many places … but too much can cause problems.
Waterlogging and salinization • Overirrigation can raise the water table high enough to suffocate plant roots with waterlogging. • Salinization (buildup of salts in surface soil layers) is a more widespread problem. • Evaporation in arid areas draws water up through the soil, bringing salts with it. Irrigation causes repeated evaporation, bringing more salts up.
Improved irrigation • In conventional irrigation, only 40% of the water reaches plants. • Efficient drip irrigation targeted to plants conserves water, saves money, and reduces problems like salinization. Figure 8.17
Solutions Soil Salinization Prevention Cleanup Flushing soil (expensive and wastes water) Not growing crops for 2-5 years Installing under- ground drainage systems (expensive) Reduce irrigation Switch to salt- tolerant crops (such as barley, cotton, sugar beet)
Fertilizers • Supply nutrients to crops • Inorganic fertilizers = mined or synthetically manufactured mineral supplements • Organic fertilizers = animal manure, crop residues, compost, etc. Figure 8.18
Global fertilizer usages • Fertilizer use has risen dramatically in the past 50 years. Figure 8.19b
Trade-Offs Inorganic Commercial Fertilizers Disadvantages Advantages Easy to transport Easy to store Easy to apply Inexpensive to produce Help feed one of every three people in the world Without commercial inorganic fertilizers, world food output could drop by 40% Do not add humus to soil Reduce organic matter in soil Reduce ability of soil to hold water Lower oxygen content of soil Require large amounts of energy to produce, transport, and apply Release the greenhouse gas nitrous oxide (N2O) Runoff can overfertilize nearby lakes and kill fish
Overgrazing • When livestock eat too much plant cover on rangelands, impeding plant regrowth • The contrast between ungrazed and overgrazed land on either side of a fenceline can be striking. Figure 8.22
Overgrazing • Overgrazing can set in motion a series of positive feedback loops. Figure 8.21
Recent soil conservation laws • The U.S. has continued to pass soil conservation legislation in recent years: • • Food Security Act of 1985 • • Conservation Reserve Program, 1985 • • Freedom to Farm Act, 1996 • • Low-Input Sustainable Agriculture Program, 1998 • Internationally, there is the UN’s “FAR” program in Asia.
Global food production World agricultural production has risen faster than human population. Figure 9.1
Global food security • However, the world still has 800 million hungry people, largely due to inadequate distribution. • And considering soil degradation, can we count on food production continuing to rise? • Global food security is a goal of scientists and policymakers worldwide.
Nutrition • Undernourishment = • too few calories • (especially developing world) • Overnutrition = • too many calories • (especially developed world) • Malnutrition = lack of nutritional requirements • (causes numerous diseases, esp. in developing world) Figure 9.2
The green revolution • An intensification of industrialization of agriculture, which has produced large yield increases since 1950 • Increased yield per unit of land farmed • Begun in U.S. and other developed nations; exported to developing nations like India and those in Africa • are more productive for plant life.
Transgenic contamination? • UC Berkeley researchers Ignacio Chapela (L) and David Quist (R) ignited controversy by claiming contamination of Mexican maize. • They later admitted some flaws in their methods, but debate continued, revealing the personal and political pressures of high-stakes scientific research. From The Science behind the Stories