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The Problem of Soil and Land Degradation

CIMMYT ®. The Problem of Soil and Land Degradation. P.C. Wall. Two major types of degradation:. Soil erosion Fertility decline

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The Problem of Soil and Land Degradation

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  1. CIMMYT® The Problem of Soil and Land Degradation P.C. Wall

  2. Two major types of degradation: • Soil erosion • Fertility decline These are linked as erosion generally removes the most fertile soil, and the processes which lead to highly erodible soils are caused largely by soil fertility decline.

  3. Effect of Tillage on Soil Erosion

  4. Soil fertility degradation What is a fertile soil? A fertile soil allows the crop to produce close to the maximum dictated by the environment (moisture and radiation) … provided other management factors are optimal.

  5. Argentinian Pampa Wheat Yield Over Time Yield (t/ha) 120-60-0 0-0-0 Years of continuous agriculture

  6. Chemical Fertility The Triangle of Soil Fertility Physical Fertility Biological Fertility Biological Fertility The forgotten parts of soil fertility

  7. Decline of Crop Yields and Profitability over Time using Conventional Agriculture 100 Relative Profitability (%) Cost of production Profitable Not Profitable 0 Years of Continuous Agriculture

  8. Problems Caused by Soil Physical Degradation • Weak aggregates • Lower soil porosity • Soil crusting and surface sealing • More soil compaction

  9. Copied from Elwell, 1989

  10. The Triangle of Soil Fertility Chemical Fertility S.O.M. Physical Fertility Biological Fertility Soil Organic Matter (soil carbon) is linked to all aspects of soil fertility and Soil Quality

  11. Effect of Conventional Agriculture on Soil Organic Matter (%)

  12. Raindrop effects (from Elwell, 1989) Time

  13. Effect of Conventional Agriculture on Water Infiltration Rates (mm/h)

  14. The surface crust impedes both water infiltration and gas interchange – especially oxygen. And so this woman farmer knows she will get benefits from breaking the crust – but that involves a lot of work!

  15. More crops per year More tillage Reduction in Soil Structural Stability Less root exploration Reduced water infiltration Soil compaction Water stress Waterlogging Soil erosion More rapid crop development High Temperatures Faster oxidation of organic matter High intensity rainfall Surface sealing Surface crusting Reduced plant populations

  16. Reduction in Soil Structural Stability Less root exploration Reduced water infiltration Soil compaction Water stress Waterlogging Soil erosion High Temperatures Faster oxidation of organic matter More tillage High intensity rainfall Surface sealing Surface crusting Reduced plant populations

  17. Reduction in Soil Structural Stability Less root exploration Reduced water infiltration Soil compaction Water stress Waterlogging Soil erosion High Temperatures Faster oxidation of organic matter More tillage High intensity rainfall Surface sealing Surface crusting The Vicious Circle Reduced plant populations

  18. Chemical Fertility The Triangle of Soil Fertility Physical Fertility Biological Fertility Biological Fertility

  19. Carbon lost as CO2 contributes to Global Warming

  20. TILLAGE-INDUCED CO2 "FLUSH" AND CURRENT CROP RESIDUE 19 days after tillage 300 2 249 250 2 185 g C/m from residue of previous wheat crop 200 TOTAL C LOST IN 19 DAYS (g C/m ) 150 129.5 106.6 99.8 100 49.9 50 0 NT CP DH MP MP+DH2 TILLAGE TYPE

  21. Long Term Study July 14 - October 9, 1998 Cumulative loss after 87 days (avg of 4 reps) Cumulative CO2 Flux ( g CO2 m-2)

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