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

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.

8. Effect of Tillage on Soil Erosion

9. 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.

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

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

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

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

17. Copied from Elwell, 1989

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

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

20. Time Raindrop effects (from Elwell, 1989)

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

22. 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!

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

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

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

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

35. Carbon lost as CO 2 contributes to Global Warming

36. 249 129.5 106.6 99.8 49.9 MP MP+DH2 DH CP NT TILLAGE TYPE 0 50 100 150 200 250 300 TOTAL C LOST IN 19 DAYS (g C/m ) 2 185 g C/m from residue of previous wheat crop 2

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