Legumes as a cover crop and source of nitrogen

Excerpt

The Greek and Chinese civilizations documented 2,500 years ago that legumes improved yields of subsequent crops (13). As with any green manure or cover crop, legumes can improve crop yields by reducing erosion, conserving water, recycling nutrients, and improving soil physical characteristics. However, the immediate yield response of crops following legumes is due mainly to the ability of many legumes (when infected with specific strains of Rhizobia bacteria) to convert atmospheric nitrogen (N) into plant proteins and other compounds containing N. Then, as the legume plant material decomposes, the N it contains is released for use by the following crop.

Crop selection and sequence are two important agricultural decisions. Conservation tillage increases the significance of the cropping scheme because residue from the previous crop typically remains on the soil surface. A wheat (Triticum aestivum) and soybean (Glycine Max) double-crop system is well adapted to conservation tillage. Wheat provides winter cover, cash income in the spring, and a summer mulch. The system is profitable and therefore popular.

Earlier plantings of other summer crops, such as corn, do not allow for harvest of winter cereals. Thus, a winter cover crop usually entails annual establishment and maintenance costs. Although the soil …