Soil, alimitedresource wedepend upon,but take forgranted
Soil Erosion What causes soil erosion? How serious of a problem is it? Good news and bad news from the U.S. What is desertification? How do salts degrade the soil?
CAUSES OF SOIL EROSIONWind WHY CARE aboutWater #1 soil erosion?People
Impacts of Soil Erosion Loss of soil fertility Sediment runoff causes problems in surface water (pollution, clog ditches, boat channels, reservoirs) #1 source of U.S. water pollution Renewable only on LONG timeframes (200-1,000yrs. for 1 inch)
Soil Erosion On Ag. land in U.S. today, soil is eroding 16 times faster than it is created
Global Soil Erosion Areas of serious concern Areas of some concern Stable or nonvegetative areas Fig. 14-7 p. 280
Causes of DesertificationOvergrazingDeforestationErosionSalinizationSoil CompactionNatural Climate Change
World Desertification Fig. 14-9 p. 282
Desertification: causes and consequences.•Occurring on 1/3 of world’s land
SALINIZATION1. Irrigation water contains small amounts of dissolved salts2. Evaporation and transpiration leave salts behind3. Salt builds up on soil
Reducing and Cleaning Up SalinizationReduce irrigationSwitch to salt-tolerant cropsFlush soilsNot growing crops for 2-5 yearsInstall underground drainage
Soil Degradation on Irrigated Land Salinization Evaporation Evaporation Transpiration Waterlogging1. Precipitation and irrigation water percolate downward2. Water table rises Waterlogging3. Bad for roots Less permeable clay layer Fig. 14-11 p. 283
What controls soil productivity? Water -infiltration, drainage, storage Nutrients/toxins (12/17) Gas Exchange -CO2 out, O2 in Strength/rooting volume Waste Disposal Seed/seedling nursery
Where is the best soil?
Where are the productive soils? We see what we know. The more we know, the more options we realize we have w/ the world’s soils.
What are some threats? Finite arable land: 1.1 billion hectares 1961 0.32 ha/p; today 0.15 ha/p; 2050 0.12 ha/p Erosion – today 12-40 Mg/ha 30% agricultural lands irreversibly damaged. Desertification – e.g., 27% China affected w/ new 2500 km2/yr. Salinization- affects 20% of world’s 250+ million hectares of irrigated lands. Contamination w/ heavy metals. Urbanization and other competing uses. Problematic off-site issues & competing uses.
Threats? Think little things. Compaction or loss of porosity. Loss soil organic matter. Loss CEC other buffering potential. Doolittle Prairie – e.g., 10% reduction in pore volume = 152 m3/ha = 2200 ft3/ac -less gas exchange, water storage, root volume; poorer nursery. -water quality & quantity, air quality
Soil Conservation What is soil conservation and how does it work? What are some methods for reducing soil erosion? Inorganic versus organic fertilizers
Soil ConservationInvolves many ways of reducing soil erosion and restoring fertility to soil.
Conventional Tillage Farmers plow the land and then break up and smoothes soil to make a planting surface Leaves soil vulnerable to erosion Midwest tillage often down in fall (winter bare)
Conservation Tillage Disturbing the soil as little as possible while planting crop Not tilling over winter Planting without disturbing soil Special equipment “inject” soil with seed, fertilizer etc. In 2003 45% of U.S. farms
Organic Fertilizer Has decreased in the U.S. due in part because most farmers no longer raise livestock and it costs too much to transport Poop Factory and Phillies Soil Inorganic fertilizers have taken off
Inorganic Fertilizers Nitrogen, Phosphorous, Potassium Grown in usage worldwide Credited with increasing crop yields (1/4 of world crops) W/o could only feed 2-3 billion people Many problems associated (see next slide)
“Conservation is a state of harmony between men andland.” - Ibid.“What greater grief than the loss of ones nativeland.” -Euripides“The land belongs to the future” -Willa Cather