楒惯摲匠污庆润-SoilsasabaseforAgriculture.ppt

Soils as a base for Agriculture Lee Burras Department of Agronomy Iowa State University Global Agriculture Science Policy Institute February 28, 2002 What are the potential constraints on soil productivity? Outline Lee’s premises What makes a soil productive? Where are the productive soils? Will the world’s soils stay productive? Summary Questions Lee’s premises We see what we know. We think about what’s important to us. Soil and weather are the abiotic foundation of plant productivity. Plant production forms the basis for health, wealth, environmental quality. 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 are the productive soils? Where is the best soil? Where are the productive soils? Will the world’s soils stay productive? What are the lessons from history? What are the threats? Are there opportunities? What are the lessons from history? Mesopotamia – “cradle of agriculture” – boomed then salinization erosion. Greece – wheat erosion ? olives grapes Rome – wheat erosion ? olives, grapes Egypt. China – 3,000 years of agriculture on loess, soil conservation 2000 BP b/c 1.2 billion tons erosion, today 2.4 billion tons. Cotton production – eastern USA for 150 years. Summary – soil productivity typically finite. 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. Is continued productivity possibl