1. C I M M Y T MR International Maize and Wheat Improvement Center The Role and Importance of Residues in Conservation Agriculture The Role and Importance of Residues in Conservation Agriculture Conservation Agriculture Training Course, Zimbabwe 2010 by Christian Thierfelder

2. C I M M Y T MR International Maize and Wheat Improvement Center  Minimum soil movement  Residue retention  Crop rotations and GMCCs  Minimum soil movement  Residue retention  Crop rotations and GMCCs Basic principles of Conservation Agriculture

3. C I M M Y T MR International Maize and Wheat Improvement Center Residues – what are we talking about? Maize stover covering a field before planting

4. C I M M Y T MR International Maize and Wheat Improvement Center What are residues? continued…. Maize residues in maize-cotton rotation

5. C I M M Y T MR International Maize and Wheat Improvement Center Sunnhemp residues (left) Cotton residues (right)

6. C I M M Y T MR International Maize and Wheat Improvement Center How to manage residues - rolled maize stalks or sunnhemp

7. C I M M Y T MR International Maize and Wheat Improvement Center The challenge – burning of stover CIMMYT Research Station

8. C I M M Y T MR International Maize and Wheat Improvement Center Competing uses for stover residues…!

9. C I M M Y T MR International Maize and Wheat Improvement Center  Water erosion  Water infiltration  Evaporation  Soil temperature  Weed control  Soil organic matter  Soil biological activity  Water erosion  Water infiltration  Evaporation  Soil temperature  Weed control  Soil organic matter  Soil biological activity The Role and Importance of Residues in CA

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11. C I M M Y T MR International Maize and Wheat Improvement Center Impact of raindrop on different soil surfaces

12. C I M M Y T MR International Maize and Wheat Improvement Center Crusting and sealing leads to rill erosion

13. C I M M Y T MR International Maize and Wheat Improvement Center Amount of soil being eroded after 7 years of bare fallow (plot size 224 m²)

14. C I M M Y T MR International Maize and Wheat Improvement Center Treatment Erosion in t ha -1 Runoff l m -2 Conventional ploughing (CP) 11.99 a 545.1 a Direct seeding (DS) 8.01 b 383.9 b Magoye ripper + M. pruriens intercropping (MR) 6.91 b 314.7 b LSD (p ≤ 0.05) 3.50 75.7

15. C I M M Y T MR International Maize and Wheat Improvement Center About 50% of rainfall is lost on conventional systems

16. C I M M Y T MR International Maize and Wheat Improvement Center 204060 80 20 40 60 80 100 2 4 6 8 Cover % Relative Erosion % Residue t/ha Erenstein, 1997. Based on data of Shaxon et al., 1989, Tripp and Barreto, 1993, and Kok and Thien, 1994. Relationshipbetween residue amount, Relationship between residue amount, ground cover and water erosion

17. C I M M Y T MR International Maize and Wheat Improvement Center  The soil needs to be permeable (no crusts)  The soil has to have pores (earthworms)  CA plots covered with residues provide for soil micoorganisms, build stable aggregates (natural swelling and shrinking) and increase the organic matter which all improve infiltration  The soil needs to be permeable (no crusts)  The soil has to have pores (earthworms)  CA plots covered with residues provide for soil micoorganisms, build stable aggregates (natural swelling and shrinking) and increase the organic matter which all improve infiltration Why soil erosion? Because water is not infiltrating!

18. C I M M Y T MR International Maize and Wheat Improvement Center Pore system has to be unsealed and easy to moisten to enable infiltration

19. C I M M Y T MR International Maize and Wheat Improvement Center Time to Pond – On-farm Results Conventional6.26b6.60b Rip-line seed11.50a a Direct Seed11.99a10.88a CV%22.723.9 SE Diff1.301.24 ShamvaZimuto

20. C I M M Y T MR International Maize and Wheat Improvement Center Infiltration is reduced on conventional systems

21. C I M M Y T MR International Maize and Wheat Improvement Center Effects of mulch rate on soil water conservation during fallow and on subsequent sorghum grain yield, Texas Source: Unger 1978 Mulch rate, tha -1 Precipitation storage, mm Sorghum yield, t ha -1 0 72 c 1.8 c 1 99 b 2.4 b 2 100 b 2.6 b 4 116 b 3.0 b 8 139 a 3.7 a 12 147 a 4.0 a

22. C I M M Y T MR International Maize and Wheat Improvement Center Mulch protects the soil from drying out!  Residues reduce radiation energy of the sun - less radiation => less evaporation  Drying forces of the wind are lower  Vapour flux from the soil into the air is reduced  Capillary uptake in the soil maintains moisture transportation from the subsoil to the soil surface  Residues reduce radiation energy of the sun - less radiation => less evaporation  Drying forces of the wind are lower  Vapour flux from the soil into the air is reduced  Capillary uptake in the soil maintains moisture transportation from the subsoil to the soil surface

23. C I M M Y T MR International Maize and Wheat Improvement Center Comparison between capillar uptake in conventional and residue covered soils  Conventional:Radiation is high at the soil surface (less cover), capillary uptake generally is not sufficient from the subsoil. The consequence is drying out of the upper layers  Residue covered:Radiation is lower, capillary uptake can be maintained. Soils supply more moisture for germination and plant growth.  Conventional:Radiation is high at the soil surface (less cover), capillary uptake generally is not sufficient from the subsoil. The consequence is drying out of the upper layers  Residue covered:Radiation is lower, capillary uptake can be maintained. Soils supply more moisture for germination and plant growth.

24. C I M M Y T MR International Maize and Wheat Improvement Center Effect of Crop Residues on Soil Temperature (10 cm Depth) Bare soil Days in August 1973 Temperature (°C ) Source : Lal, 1978

25. C I M M Y T MR International Maize and Wheat Improvement Center Effects of different residues on weed soil cover (in %) and weed population (plants/m 2 ) 7 and 58 day after roling Source: Almeida and Rodríguez, 1985

26. C I M M Y T MR International Maize and Wheat Improvement Center Residues build up the humus in the soil „The organic matter in tropical soils is, besides moisture, more important than any other soil characteristic“ Young, 1976

27. C I M M Y T MR International Maize and Wheat Improvement Center  Residues increase organic carbon content over time  Plant available phosphorus, potassium, calcium and magnesium increases have been reported  Residues may lead to nitrogen lock-up initially especially when soils are very limited in nitrogen (microbes use the nitrogen for their biomass)  After some years the system is in equilibrium, N immobilization will no longer negatively effect nutrient availability  Residues increase organic carbon content over time  Plant available phosphorus, potassium, calcium and magnesium increases have been reported  Residues may lead to nitrogen lock-up initially especially when soils are very limited in nitrogen (microbes use the nitrogen for their biomass)  After some years the system is in equilibrium, N immobilization will no longer negatively effect nutrient availability Effects of residues on nutrient availability

28. C I M M Y T MR International Maize and Wheat Improvement Center  Decomposition in tropical climate  Surface effects (protection, temperature, moisture retention, fodder for soil fauna and flora)  Slow nutrient release  Build-up of organic matter pool  Decomposition in tropical climate  Surface effects (protection, temperature, moisture retention, fodder for soil fauna and flora)  Slow nutrient release  Build-up of organic matter pool Why is surface residue retention important?

29. C I M M Y T MR International Maize and Wheat Improvement Center 40% 32% Microbial Decomposition Ash CO 2 Soil OM 8% Crop Residue CO 2 92%60% Burn Soil OM Crop Residue Microbial Decomposition CO 2 80% 20% No Burn Source: Albrecht et al., 1994 USDA-ARS Pendleton, OR

30. C I M M Y T MR International Maize and Wheat Improvement Center Residues encourage earthworm activity

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32. C I M M Y T MR International Maize and Wheat Improvement Center Effective destruction by ants and termites, fungi and bacteria

33. C I M M Y T MR International Maize and Wheat Improvement Center  Lignin content  C:N ratio  Microbial preferences (maize/sunflower)  Microbial variability (clay soils)  Soil moisture content  Temperature  pH  Lignin content  C:N ratio  Microbial preferences (maize/sunflower)  Microbial variability (clay soils)  Soil moisture content  Temperature  pH Factors influencing decomposition

34. C I M M Y T MR International Maize and Wheat Improvement Center Effect of residue addition on biological activity (% increase in biological activity over control) Day Wheat straw burned stubbles 1 80 29 4 619 7 470 10 280 Source: Albrecht et al., 1994 USDA-ARS Pendleton, OR

35. C I M M Y T MR International Maize and Wheat Improvement Center Problems and challenges with residues (pests and diseases carry over) Perithecia of Pyrenophora trichostoma (Helminthosporium tritici- repentis) on wheat straw

36. C I M M Y T MR International Maize and Wheat Improvement Center Residues increase micro-, meso,- and macro-fauna thus facilitating a biological equilibrium If a system is in equilibrium, insects and pests are controlled by their predators

37. C I M M Y T MR International Maize and Wheat Improvement Center Some people just prefer „clean“ fields The mindset is very important

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39. C I M M Y T MR International Maize and Wheat Improvement Center Thank you very much!