Soil – A Renewable Resource Chapter 13: Food, Soil, Conservation, and Pest Management March 2009

What is Soil? “Soil is a thin covering over most land that is a complex mixture of eroded rock, mineral nutrients, decaying organic matter, air, and billions of living organisms” Produced by physical, chemical, and biological weathering Bedrock is broken down, then organisms such as lichen add nutrients. Takes a very long time to develop the various layers of soil (100 years for topsoil) Basis for life on land – provides nutrients to primary producers and so on. Recycles dead and decaying materials and thus serves as a carbon sink.

Soil Horizons Mature soils that have developed over a long time are arranged in a series of horizontal layers called soil horizons. Each has a distinct texture and composition. A cross section of the horizons is called a soil profile Most mature soils have at least three layers. O horizon – surface litter layer – freshly fallen undecomposed or partially decomposed leaves, twigs, crop wastes, animal waste, fungi, and other organic materials (brown to black) A horizon – topsoil layer – porous mixture of partially decomposed bodies of dead plants and animals called humus. May contain silt, clay or sand.fertile O and A concentrate the organic material and hold most roots and absorb and release most of the water Most developed soils teem with organisms Breakdown and recycle nutrients, dissolve them in water, make them available to plant life Color of topsoil suggests how useful it is. – dark brown or black are rich in N and organic material B horizon – subsoil – consists of silt, clay, or gravel that has been broken down. C horizon – parent material – sits on a base of bedrock, the ultimate parent supplier of fragments B and C are inorganic layers Create spaces or pores through which air can reach the roots of plants

Layers in Mature Soils Infiltration: the downward movement of water through soil. Leaching: dissolving of minerals and organic matter in upper layers carrying them to lower layers. The soil type determines the degree of infiltration and leaching.

Desert Soil (hot, dry climate) Grassland Soil semiarid climate) Mosaic of closely packed pebbles, boulders Weak humus-mineral mixture Alkaline, dark, and rich in humus Dry, brown to reddish-brown with variable accumulations of clay, calcium and carbonate, and soluble salts Figure 3.24 Natural capital: soil profiles of the principal soil types typically found in five types of terrestrial ecosystems. Clay, calcium compounds Desert Soil (hot, dry climate) Grassland Soil semiarid climate) Fig. 3-24a, p. 69

Tropical Rain Forest Soil (humid, tropical climate) Acidic light-colored humus Figure 3.24 Natural capital: soil profiles of the principal soil types typically found in five types of terrestrial ecosystems. Iron and aluminum compounds mixed with clay Tropical Rain Forest Soil (humid, tropical climate) Fig. 3-24b, p. 69

Deciduous Forest Soil (humid, mild climate) Forest litter leaf mold Humus-mineral mixture Light, grayish-brown, silt loam Figure 3.24 Natural capital: soil profiles of the principal soil types typically found in five types of terrestrial ecosystems. Dark brown firm clay Deciduous Forest Soil (humid, mild climate) Fig. 3-24b, p. 69

Coniferous Forest Soil Acid litter and humus Light-colored and acidic Figure 3.24 Natural capital: soil profiles of the principal soil types typically found in five types of terrestrial ecosystems. Humus and iron and aluminum compounds Coniferous Forest Soil (humid, cold climate) Fig. 3-24b, p. 69

Soil Properties Particle size: clay, silt, and sand Soil texture: relative amounts of each different particle size Porosity: how well water infiltrates the soil Soil Moisture: how much water is retained in the soil % Organic Matter Percolation Rate – how fast water infiltrates the soil

Silt Clay Sand less than 0.002 mm Diameter 0.002–0.05 mm diameter Water Water 0.05–2 mm diameter Figure 3.25 Natural capital: the size, shape, and degree of clumping of soil particles determine the number and volume of spaces for air and water within a soil. Soils with more pore spaces (left) contain more air and are more permeable to water than soils with fewer pores (right). High permeability Low permeability Fig. 3-25, p. 70

SOIL EROSION AND DEGRADATION Soil erosion is the movement of soil components, especially surface litter and topsoil, by wind or water. lowers soil fertility overload nearby bodies of water with eroded sediment. increases through activities such as farming, logging, construction, overgrazing, and off-road vehicles.

TYPES OF SOIL EROSION Sheet erosion: surface water or wind peel off thin layers of soil. Rill erosion: fast-flowing little rivulets of surface water make small channels. Gully erosion: fast-flowing water join together to cut wider and deeper ditches or gullies. Soil erosion – movement of soil components

Sheet erosion

Rill erosion

Gully erosion

Global Outlook: Soil Erosion Soil is eroding faster than it is forming on more than one-third of the world’s cropland. Eroding faster than it was being created on 38% of the world’s cropland. Soil erosion can increase a country’s need for importing food and cause intense competition among nations for food. Soil erosion costs $375 billion per year ($45 billion /year in US) Figure 13-10

Soil Erosion in the U.S. Soil erodes faster than it forms on most U.S. cropland, but since 1985, has been cut by about 40%. 1985 Food Security Act (Farm Act): farmers receive a subsidy for taking highly erodible land out of production and replanting it with soil saving plants like grasses and trees for 10-15 years.

Desertification “Occurs when the productive potential of drylands falls by 10% or more because of a combination of natural climate change that causes drought and human activities that reduce or degrade topsoil.” Natural oscillating process that has been accelerated by human activities Affects 1/3 of world’s land and 70% of all dry lands.

(10-25% drop) Moderate Severe Very severe (>50% drop) (25-50% drop) Figure 13.11 Natural capital degradation: desertification of arid and semiarid lands is caused by a combination of prolonged drought and human activities that expose soil to erosion. QUESTION: What three things would you do to reduce desertification? (Data from UN Environment Programme and Harold E. Drengue) Moderate (10-25% drop) Severe (25-50% drop) Very severe (>50% drop) Fig. 13-11, p. 280

Causes and Consequences of Desertification Overgrazing Worsening drought Deforestation Famine Erosion Economic losses Salinization Lower living standards Soil compaction Natural climate change Environmental refugees Figure 13.12 Natural capital degradation: causes and consequences of desertification. QUESTION: How serious is the threat of desertification where you live? Fig. 13-12, p. 280

Salinization and Waterlogging Salinization results from repeated irrigation in dry climates where salts gradually accumulate in the upper soil layers. Waterlogging occurs when farmers apply too much irrigation water to leach salts deeper into the soil. Figure 13-13

The Effects of Soil Salinization Figure 13-14

Solutions Soil Salinization Prevention Cleanup Reduce irrigation Flush soil (expensive and wastes water) Stop growing crops for 2–5 years Figure 13.15 Solutions: methods for preventing and cleaning up soil salinization. QUESTION: Which two of these solutions do you think are the most important? Switch to salt-tolerant crops (such as barley, cotton, sugarbeet) Install underground drainage systems (expensive) Fig. 13-15, p. 281

SOIL CONSERVATION Soil conservation involves reducing soil erosion and restoring soil fertility mostly by employing vegetation. Conservation tillage Strip cropping/contour planting Terracing Alley cropping Shelter breaks/windbreaks Cover crops Livestock rotation

Conservation Tillage Conservation-tillage farming: Increases crop yield. Raises soil carbon content. Lowers water use. Lowers pesticides. Uses less tractor fuel.

Strip Cropping/ Contour Planting

Terracing

Alley Cropping

Shelter Belts

Cover Crops

Cover Crops Planting of a grass or grain that establishes well in fall and winter on a field shortly before (early) or not long after (late) the main cash crop has been harvested

Cover Crops Benefit Ground and Groundwater Reduce nutrient concentrations in groundwater. Promotes root growth of subsequent cash crop especially in compacted soils. Especially effective against nitrogen.

Costs of Cover Crops Costs Hairy vetch and winter rye at Clagett Farm Costs Require extra management by the farmer in order to perform well Not always an available market/use for the cover crop Few programs advocate for them in MD and VA Requires farmers to incur the cost of the cover crop (seeds) – Horton estimates this at $56 million/year in Chesapeake Bay watershed In 2005, Gov. Robert L. Ehrlich Jr. provided $5 million in grants to MD farmers to plant cover crops through the Maryland Agricultural Water Quality Cost-Share (MACS) Program .

Livestock Rotation the movement of cattle or other grazing livestock from pasture to pasture Benefits Prevents over-grazing of pastureland and excess soil erosion Reduces the need for equipment intensive “hay” operations and the expense of fertilizers and pesticides that go with them Cattle require fewer medicines, antibiotics, and hormones Rotation of livestock reduces the impact of animal waste and reduces run-off of nutrients Produce healthier meat products In addition, converting crop land into pasture can broaden a farm’s economic base. Costs Often means a reduction in gross sales for the farmer Reduces the amount of land farmer has for crop production

SUSTAINABLE AGRICULTURE THROUGH SOIL CONSERVATION Fertilizers can help restore soil nutrients, but runoff of inorganic fertilizers can cause water pollution. Organic fertilizers: from plant and animal (fresh, manure, or compost) materials. Commercial inorganic fertilizers: Active ingredients contain nitrogen, phosphorous, and potassium and other trace nutrients.