Page 98 - Soil Degradation, Conservation and Remediation

3.4 Control of Water Erosion 85

Fig. 3.8 Cover crops on a field in Black Hawk County, Iowa (Photo courtesy of USDA-NRCS)

yields, (viii) recycling nutrients, (ix) preventing leaching of nutrients, and (x)
improving water quality (Blanco and Lal 2008 ). Cover crops are mainly grown
between the cropping seasons. They can also be grown as rotational crops and
companions to main crops. Cover crops may include suitable grasses and legumes.
When legumes are grown as cover crops, biological nitrogen fixation may benefi t

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the succeeding crop. Field legumes may fix 200–300 kg N ha year . Use of mixed
cover crops, including grasses and legumes, increases the biomass return to the soil,
enhances activity of soil organisms, and improves soil productivity. Use of cover
crops not only reduces runoff, soil erosion, and use of inorganic fertilizers but also
controls weeds, a major constraint in reduced and no-till systems. Establishing
cover crops is one of the top conservation practices for reducing runoff and soil
erosion from agricultural soils (Fig. 3.8 ).
High seed rates and fertilizers and manures are used to obtain a dense stand of
cover crops. Incorporation of cover crop as a green manure is recommended prior to
blooming. Green manuring with leguminous cover crops while they are tender
improves decomposition, increases biological activity, causes a rapid nutrient
release, and improves supply of nitrogen for the next crop. Cover crops must be
incorporated into the soil several weeks prior to planting the main crops to minimize
risks of drought stress in semiarid and arid regions and to avoid competition for
nutrients by decomposing microorganisms. Retaining cover crops as mulch is more

benefitting than plowing under in soils where the erosion rate is high. Cover crop
mulch on the soil surface increases soil organic matter content and suppresses weeds
in addition to protection against erosion (Blanco and Lal 2008 ).