Alfalfa in rotation

Benefits of alfalfa in the rotation

Alfalfa provides many benefits to the crop rotation. Some of these benefits occur during the years that alfalfa is in production and others occur during the crops that follow alfalfa. These include:

• Increased soil organic matter
• Decreased soil erosion
• Decreased soil nitrate loss

Biological N fixation

About 80 percent of the earth's atmosphere is nitrogen gas (N₂). Unfortunately, nitrogen gas is unusable by most living things and living things do need nitrogen!

All organisms need ammonia (NH₃) , one of the forms of nitrogen, for building proteins and other components to live and grow.

Biological nitrogen fixation changes the inert, unusable gas to the biologically usable form, ammonia. In alfalfa, this process is mediated by rhizobia bacteria in a symbiotic relationship. The soil bacterium invades the root and causes a nodule to grow. The plant supplies energy and nutrients to the nodule, and in return, the bacterium changes the atmospheric nitrogen to usable ammonia for the plant.

On average, alfalfa fixes 150 to 200 pounds of nitrogen per acre per year. It provides most of the nitrogen the alfalfa needs during its production years. When the alfalfa is terminated, the nitrogen in the residue, along with increased soil N, supplies a large amount of nitrogen to the following crop.

This increased N supply can often eliminate the need for fertilizer nitrogen for the following crop in the first year after alfalfa and reduce that need in the 2nd year.