Soil – A Renewable Resource

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

2. 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

3. Soil Horizons

4. 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.

5. 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 Clay, calcium compounds Desert Soil (hot, dry climate) Grassland Soil semiarid climate) Fig. 3-24a, p. 69

6. Acidic light-colored humus Iron and aluminum compounds mixed with clay Tropical Rain Forest Soil (humid, tropical climate) Fig. 3-24b, p. 69

7. Forest litter leaf mold Humus-mineral mixture Light, grayish-brown, silt loam Dark brown firm clay Deciduous Forest Soil (humid, mild climate) Fig. 3-24b, p. 69

8. Acid litter and humus Light-colored and acidic Humus and iron and aluminum compounds Coniferous Forest Soil (humid, cold climate) Fig. 3-24b, p. 69

9. 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

10. Silt Clay Sand less than 0.002 mm Diameter 0.002–0.05 mm diameter Water Water 0.05–2 mm diameter High permeability Low permeability Fig. 3-25, p. 70

11. 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.

12. 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.

13. Sheet erosion

14. Rill erosion

15. Gully erosion

16. Global Outlook: Soil Erosion Figure 13-10

17. 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.

18. 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.

19. Moderate (10-25% drop) Severe (25-50% drop) Very severe (>50% drop) Fig. 13-11, p. 280

20. Causes and Consequences of Desertification Causes Consequences Overgrazing Worsening drought Deforestation Famine Erosion Economic losses Salinization Lower living standards Soil compaction Natural climate change Environmental refugees Fig. 13-12, p. 280

21. 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. Salinization and Waterlogging Figure 13-13

22. The Effects of Soil Salinization Figure 13-14

23. Solutions Soil Salinization Prevention Cleanup Reduce irrigation Flush soil (expensive and wastes water) Stop growing crops for 2–5 years Switch to salt-tolerant crops (such as barley, cotton, sugarbeet) Install underground drainage systems (expensive) Fig. 13-15, p. 281

24. 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

25. Conservation Tillage

26. Strip Cropping/ Contour Planting

27. Terracing

28. Alley Cropping

29. Shelter Belts

30. Cover Crops

31. 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

32. 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.

33. Costs of Cover Crops 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 .

34. Livestock Rotation • 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 • 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

35. 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.