Less permeable clay layer Transpiration Evaporation Evaporation Evaporation Waterlogging Less permeable clay layer Salinization Figure 13.13 Natural capital degradation: salinization and waterlogging of soil on irrigated land without adequate drainage can decrease crop yields. Waterlogging 1. Irrigation water contains small amounts of dissolved salts 1. Precipitation and irrigation water percolate downward. 2. Evaporation and transpiration leave salts behind. 2. Water table rises. 3. Salt builds up in soil. Fig. 13-13, p. 281

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

Salinization and Waterlogging of Soils: A Downside of Irrigation Example of high evaporation, poor drainage, and severe salinization. White alkaline salts have displaced cops. Figure 13-14

Erosion Control (see Miller pg. 282) Shelterbelts – can reduce wind erosion. Long rows of trees are planted to partially block the wind. They can also help retain soil moisture, supply some wood for fuel, and provide habitats for birds.

Minimum Tillage – (conservation tillage) to disturb the soil as little as possible while planting crops. Special tillers break up and loosen the subsurface soil without turning over the topsoil, previous crop residues, and any cover vegetation.

SUSTAINABLE AGRICULTURE THROUGH SOIL CONSERVATION Modern farm machinery can plant crops without disturbing soil (no-till and minimum tillage. Conservation-tillage farming: Increases crop yield. Raises soil carbon content. Lowers water use. Lowers pesticides. Uses less tractor fuel.

Contour Farming –sloping your growing crops, etc. You run terraces parallel to the ground to stop soil from running down a steep slope. Plowing and planting crops in rows across, rather than up and down, the sloped contour of the land.

Terracing – (what you use for contour farming Terracing – (what you use for contour farming.) Dirt goes up to hold the dirt in place. Broad, nearly level terraces that run across the land contour. Helps to retain water for crops at each level and reduce soil erosion by controlling runoff.

SUSTAINABLE AGRICULTURE THROUGH SOIL CONSERVATION Terracing, contour planting, strip cropping, alley cropping, and windbreaks can reduce soil erosion. Figure 13-16

Strip Cropping – a row crop such as corn alternates in strips with another crop that completely covers the soil, reducing erosion. It catches and reduces water runoff and helps prevent the spread of pests and plant diseases.