Legume crop great fit for area

Looking for a crop that can disrupt weeds and insects, boost the level of beneficial nitrogen in the soil and perhaps produce a protein-rich forage crop for dairy cows? Consider legumes.

Legumes are a group of broadleaf plant species that possess the unique ability of fixing nitrogen directly from the atmosphere. These crops do not need costly nitrogen fertilizer applications and often leave some nitrogen for the next crop, which is commonly called the “nitrogen credit.”

Although legumes are widely adopted, they are not intensively used in cropping systems across the country. The only exceptions are alfalfa and soybeans, which are widely grown but need more water than most legumes.

Rising fertilizer costs, rising fuel costs, increasing knowledge of the multiple benefits of legumes and the increasing need for plant-based protein by the growing animal industry all favor increased adoption of legumes in the United States.

The most commonly reported benefit of a legume crop is the ability to add nitrogen to the ecosystem, which is renewable and energy efficient.

The symbiotic relationship of legumes with a group of bacteria called Rhizobium, which forms reddish- to pink-colored nodules on the roots of legumes, is responsible for fixing nitrogen. Rhizobium provides nitrogen to legumes in return for food. The quantity of nitrogen that is fixed varies from zero to several hundred pounds per acre. The factors that influence nitrogen fixation include crops and cultivars, soil type, texture, pH, nitrate levels in the system, temperature, water, availability of other nutrients, and harvest management of crops.

Each legume species needs a specific Rhizobium strain. Often the required Rhizobium strain will not be in a soil, especially when the legume crop selected is not frequently grown or the locally adopted Rhizobium is not a good nitrogen fixer. Therefore, appropriate Rhizobium strains should be used for inoculation into soils.

Often, grain crops are reported to produce 10- to 20-percent higher yields following a legume crop compared with the production of continuous grain crops. Adjusting nitrogen levels by application of more nitrogen to cereal crop after cereal crop cannot completely explain yield improvement. This suggests other rotational benefits are also playing a role.

Acidification of the rhizosphere by legumes is reported to increase nutrient availability including phosphorus. Legumes also break insect, disease and weed cycles. Legumes in a system also help the environment by sequestering carbon and reducing pollution.

Legumes as a cover crop can sequester nitrogen and reduce erosion problems. Overall, legumes in the cropping system can increase the sustainability of agriculture.

The agriculture scenario in New Mexico provides a lot of opportunities for using legumes in the system. The large dairy industry in the state can use protein-rich legume forage and grains. Identifying suitable legume crops for cover cropping can protect soil from erosion and fix nitrogen, and the residue can protect grain crop seedlings from sand blasting.

Designing legume-based cropping systems can provide nitrogen and non-nitrogen rotational benefits to the system. Research has indicated that in an intercropping situation, nitrogen from the legume is available for a grain crop. This intercropping can be a good strategy to improve resource use efficiency of cropping systems. If used for a forage production system, then the livestock industry can benefit from improved forage quality. Thus, legumes offer lots of opportunities and it is up to us to make the best of it.

Sangu Angadi is a crop physiologist for New Mexico State University at the Agricultural Science Center at Clovis. He can be reached at 985-2292 or e-mail angadis@nmsu.edu.