Nitrogen fertilizer management is important for the success of any crop.  It is an expensive input, so growers are always looking for the best way to reduce application costs while still increasing yields. Nitrogen fertilizer is produced from natural gas, which makes the cost of the fertilizer vulnerable to changes in the supply and price of the gas. High yield crops have a high nitrogen requirement. However, some crops are able to supply their own nitrogen, while adding more to the soil for future crops.

Legume crops are able to generate their own nitrogen through a process called nitrogen fixation. Nitrogen fixation takes place when a specific soil bacteria called rhizobia comes into contact with the root hair of the legume. The rhizobia infects the root, colonizes and grows within it, creating structures called nodules on the roots. They begin to take nitrogen from air within the soil and supply it directly to the plant. In return, the plant provides food for the bacteria, creating a mutual relationship between them.

Different legumes are able to fix different amounts of nitrogen. Soybeans can produce 50% of their total nitrogen needs. Fababeans can produce as much as 90%. The amount of nitrogen that is fixed by these crops depends on how many bacteria are available in the soil to infect the roots. Population numbers will vary between fields, so many farmers will take advantage of seed inoculant products which add high numbers of rhizobia bacteria directly into the soil and near the roots.

A second benefit provided by legume crops is that they will add nitrogen to the soil that can be used by future crops. Nitrogen is released into the soil by the roots, and is left behind during the decay and breakdown of the plant matter. The total amount of nitrogen added to the soil will depend on how much nitrogen was fixed by the crop, and how dense the plant population was. A healthy stand of alfalfa can potentially add up to 140 lbs of nitrogen per acre. Soybeans can commonly provide 30 lbs of nitrogen per acre for the following crop. If followed by corn, this can supply roughly 25% of the nitrogen needs for a 100 bu/ac crop. Making sure their legume crop is well-nodulated offers multiple benefits for farmers.

Image source: XiteBio Technologies Inc.