The use of cover crop
A cover crop can be sown between cropping operations or as a companion crop during the early stages of crop development. An example of a cover crop system used in the Philippines is sowing mungbean with maize. The mungbean are either sowed at the same time with maize as intercrop or as relay cropping or a crop after maize (crop rotation). There is however some difficulties in the use of cover crops. One is competition for soil moisture and sunlight with the cash crop.
Maintaining ground cover either as an intercrop, relay, or crop in rotation is critical in reducing the effects of raindrop impact and soil aggregate disintegration. Ground cover prevents raindrops from directly striking the soil surface and allows rainfall to slowly penetrate the soil surface. Thus, reducing the amount of rainfall that goes to runoff and make more water available for plant growth.
There are a number of options to maintain vegetation or cover during and between cropping operations. One is stubbles retention; retaining surface stubble provides ground cover and organic matter during fallow periods and successive crops. Advantages of stubble include no competition with the crop in terms of moisture and reduced herbicide use. However, there could be some difficulties in sowing seeds directly to the crop stubbles specially ion thick-stubbles. These difficulties with tillage and sowing through the stubble may be overcome by finely chopping the stubble before sowing and modifying direct drilling equipment.
Employing direct seeding (Minimum Tillage)
Direct seeding into crop residues, reduces tillage and cultivation costs, increases organic matter inputs, increases ground cover, and reduces time and labor. Direct seeding is appropriate for all soil types provided it is well managed with respect to soil moisture, stubble preparation and appropriate use of machinery. The success of direct seeding is largely determined by the amount of organic matter which can be incorporated into the surface soils. Under good management, the natural soil tilth of the surface layers should improve with the increased organic matter levels.
Addition of organic matter
Soil organic matter is important for good crop production and preventing erosion. Organic matter binds individual soil particles into large stable aggregates which resist erosion. Soils with stable aggregates are able to withstand the forces of raindrop impact and dispersion and have more and better connected pore spaces which transmit water from the soil surface reducing runoff.
Erosion may be prevented by adopting cropping systems which either prevent the loss of organic matter, or return organic inputs back into the soil. Organic matter is lost from the soil by oxidation during tillage and cultivation operations. Means to minimize organic matter loss include; direct seeding, reduced use of powered tillage implements, reduced cultivation, appropriate herbicide use and longer fallows.
Inclusion of green manure crops in the cropping system
Organic matter may be returned to the soil by incorporating green manure crops into cropping rotations. Green manure crops are turned back into the soil to be broken down into organic matter. As well as returning organic matter to the soil, green manure crops provide cover against erosion, biological ripping to improve soil structure, suppress weeds and fix atmospheric nitrogen (legumes). The amount of organic matter returned to the soil depends on the amount of vegetative material, soil biological activity and climate factors. Typically a green manure of 6 t/ha dry matter returned to the soil, about 25% would be converted to organic matter, resulting in a return of 1.5t/ha organic matter or 0.075% increase in organic matter to a 20cm thick topsoil.
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