It takes as much as 300 pounds of nitrogen per acre to produce a yield of 75 bushels of soybeans. To make sure plants are capable of utilizing the available nitrogen producers need to check soybean root systems. The professionals say whether a commercial inoculant was applied to the seed or not, conducting in-field evaluations of soybean root nodulation can provide growers insight on how to increase yield potential the next time soybeans are planted in that field.
Jim Beuerlein, a retired Ohio State University Extension agronomist, notes some of the nitrogen comes from oxidation of organic matter in the soil, but the balance is produced by rhizobia bacteria residing in nodules on the plant's roots. Beuerlein says soybean roots need to be properly inoculated with the right strain of rhizobia to effectively and efficiently provide the nitrogen needed for maximum yield.
To conduct an effective soybean root nodulation evaluation start checking plants 40 days following emergence and until pods begin to fill. Carefully remove soil from around the root system, then soak roots in a bucket of water and gently remove the remaining soil. Examine the area around the tap root. There should be at least eight to 20 large healthy nodules per plant. Beuerlein says if too few nodules are found and plants appear pale green in color, consider the use of a soybean seed treatment containing an inoculant component before planting soybeans again in that location.