Nodulation

Legume nodulation is not well understood.  Word processors don't even recognize the word nodulate.  Definition: 

1. to cause the formation of nodules on or in nodulating

several different legumes>. intransitive verb. : to form or multiply in nodules ...

"Nodules on many perennial legumes, such as alfalfa and clover, are finger like in shape. Mature nodules may actually resemble a hand with a center mass (palm) and protruding portions (fingers), although the entire nodule is generally less than 1/2 inch in diameter. Nodules on perennials are long-lived and will fix nitrogen through the entire growing season, as long as conditions are favorable. Most of the nodules (10-50 per large alfalfa plant) will be centered around the tap root.

Nodules on annual legumes, such as beans, peanuts and soybeans, are round and can reach the size of a large pea. Nodules on annuals are short-lived and will be replaced constantly during the growing season. At the time of pod fill, nodules on annual legumes generally lose their ability to fix nitrogen, because the plant feeds the developing seed rather than the nodule. Beans will generally have less than 100 nodules per plant, soybeans will have several hundred per plant and peanuts may have 1,000 or more nodules on a well-developed plant."

"Soybeans have a high demand for nitrogen. Approximately, five pounds of nitrogen is required to produce a bushel of soybeans. Fortunately for soybean producers, most of this nitrogen is provided through biological fixation of atmospheric nitrogen by bacteria living in colonies (nodules) on the soybean roots. Biological fixation accounts for 50 to 75 percent of the soybean crops’ total nitrogen requirement. The remainder is obtained from the soil.

Because biological fixation is the major source of nitrogen for soybeans, producers should evaluate a few soybean plants in each field to determine if nodules are present in sufficient numbers and actively fixing nitrogen. This is easy to do and the information gained can be used to correct an in-season nitrogen deficiency or develop strategies for improving nodulation the next time soybeans are grown in the field.

Begin checking roots for nodules about five to six weeks after planting. The nodules should be large and active by this time and supplemental nitrogen fertilizer can still be applied if needed. Always use a shovel to carefully remove as much of the root system as possible from the soil. Dig up at least 10 plants from representative areas in each field and immerse the roots in water to remove the soil. 

Yesterday on our scouting trip we found everything from no nodules to a few small gray ones, to 10-20 large healthy nodules per plant.  I like to see a cluster of nodules on a large root just below the soil and a smaller ones scattered among a healthy root system.  A soybean should not easily pull out of the ground and should require digging at 8 weeks.  Some did yesterday and some you could pluck right out of the soil.

My question for you today is how are your legume crops nodulating?  From garden peas to soybeans, do you have the best environment for nodulation?

Ed Winkle