If your nodules are green/grey on the inside, this means they are inactive or not fixing N. If the inside is pink, then N fixation is taking place (Fig.

Slice a root nodule in half and check the color of the interior.

Gently wash or break away the soil for the roots to reveal the nodules (Fig.

Carefully dig out a plant with the roots and surrounding soil still intact.

It takes this long for nodules to form and N fixation to begin. So how do you know if your inoculant is working? How do you know that nodules have formed and are fixing N?Ĭhecking your plants for effective nodulation is a straight forward process: This is one of the reasons why adding a legume crop to your crop rotation is recommended as a way to generate soil fertility benefits for future crops. For example, a dense soybean crop that has optimal nodulation/N-fixation can add 30-50 lbs/ac of N back into the soil (4). A portion of the N fixed by legume crops will be left behind in the soil during the decay and breakdown of leftover plant matter after harvest. The substantial N-fixation of a legume crop not only benefits the crop itself, but also the field it is grown in. To ensure this population exists, it is usually recommended to apply a rhizobial inoculant every year during seeding. A large population of fresh, active bacteria that are in an optimal state to nodulate your crop roots are required to have the best results. The amount of N these crops can get through this process depends on the population of healthy rhizobia in the soil. Soybeans can get up to 60% of their required N through N-fixation, while Peas, Lentils and Faba beans can get up to 80% (3). The amount of N fixed by a successfully nodulated crop is substantial.

In certain soils, these bacteria that are specific to each crop, often do not exist naturally or sometimes not in adequate number and must be added in the form of bacterial inoculants, something all legume farmers are generally familiar with. In return, the plant provides food for the bacteria, creating a mutual or symbiotic relationship between them. Within these nodules, the rhizobia take N from air within the soil and supply it directly to the plant. When specific soil bacteria (called rhizobia) come into contact with a root hair of a legume, it can colonize the root and form a symbiotic structure called a nodule. Legumes have evolved a clever way of getting this high N requirement naturally: the use of N-fixing bacteria. For example, a 35 bu/ac soybean crop will uptake 160-200 lbs/ac of N from the soil and a 50 bu/ac pea crop will uptake 138-168 lbs/ac of N (2). In this week’s edition of Growing Possibilities, we will be looking at root nodules: what they are and how they help not only your crop, but your field itself.Ī high yielding crop requires a large amount of N, and legumes have some of the highest N requirements in row crops. But root nodules do more than just provide N to the host plant, they can put some of that N back into the field as well. Legume crops are able to get their own N through root nodules containing N-fixing bacteria, which supply the plant with N pulled right from the air.

One group of popular row crops has a way around heavy N inputs. The price of all major N fertilizers are up between 7-11% compared to this time last year, so growers are looking for the best way to reduce application costs while still increasing yields now more than ever (1). It is an expensive input, with this season‘s prices especially high. Nitrogen (N) fertilizer management is important for the success of any crop.

Root cropit