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One of the most important decisions a farmer has to make is how to manage his crop rotation. Moving around the seeded crops helps to keep a proper balance of nutrients in the soil. Although these can be supplemented with fertilizers, proper crop rotation is still very important. One key nutrient that is enriched by some crops and depleted by others is nitrogen.
Alfalfa puts more nitrogen back into the soil than almost any other crop that you might use. The only downside to alfalfa is that much of the nitrogen produced is removed during the harvest. Despite this removal, however, the crop still provides a great deal of added nitrogen to the soil that the following crop can access. Approximately 50 lbs. of nitrogen per acre are added to the soil based on a year of growing alfalfa on a given field.
Chickpeas increase the content of soil nitrogen in the season following their growth. Chickpeas are a good crop to grow also because they don't require fertilization in most cases, which makes them cost-effective. A wide range exists in regard to the estimation of how much nitrogen chickpeas put into the soil; however, the net result should always be a gain. Expect to get from between 37 to 240 lbs. of nitrogen per acre.
Soybeans are used by some farmers to help replenish nitrogen in the soil after growing a crop that consumes a great deal of nitrogen, such as corn. Soybeans hold an advantage over some other legumes in terms of nitrogen fixation because of the number of nodules that the plants form. The nodules are small growths on the roots of the plant that store nitrogen the plant gathers from the air. Most bean varieties only grow a hundred or less nodules on a single plant, but a soybean plant can grow several hundred. This makes soybeans a valuable nitrogen source.
Peas offer a good option for fixing nitrogen into the soil. Some farmers employee what is known as a "green manure" strategy when growing legumes. This means instead of harvesting them, they plow the crops back into the soil as fertilizer. This ensures all the nitrogen goes back into the soil instead of only the portion that is not harvested. Field peas put as much as 178 lbs. of nitrogen per acre back into the soil when used as green manure.
- NDSU Agriculture; Crop Rotations for Increased Productivity; Dr. Michael D. Peel; January 1998
- Confolio: Chickpeas
- New Mexico State University; Nitrogen Fixation by Legumes; W.C. Lindemann et al; May 2003.
- Government of Alberta: Improving Soil Fertility With Green Manure Legume Crops - Frequently Asked Questions