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Searching for the Best Combination of Nitrogen Fertilizers and Inoculation for Dry Edible Bean Production
April 15, 2003

George Rehm
Department of Soil, Water, and Climate, University of Minnesota

Use of nitrogen fertilizer will increase dry edible bean production. If properly inoculated this crop can also utilize nitrogen from our atmosphere. If nitrogen in soil is excessive, nodules become lazy and do not work. There may be a combination of inoculation and applied nitrogen that will optimize production. This research project was conducted in an effort to find that combination.

Navy, red kidney, and pinto beans were planted in fields of four cooperating bean producers. The beans were fertilized with 0, 30, 60, 90, 120 lb. N/acre either with or without inoculation at planting.

In all four fields, yield was not affected by seed inoculation which was completed in the field just prior to planting. Examination of roots revealed that there was nodule growth on all root systems even though some beans had not been inoculated just prior to planting.

Bean yields increased as the rate of applied nitrogen increased. Seed inoculation had no effect on the magnitude of the yield increase. At all locations, the optimum rate of fertilizer nitrogen varied between 90 and 120 lb. per acre. The yield increase produced by use of this rate of nitrogen averaged 578 lb. per acre., 545 lb. per acre and 601 lb. per acre for the navy, pinto, and red kidney beans respectively. Using current prices for edible beans and nitrogen fertilizer, the return after fertilizer purchase was $19.80, $34.70 and $70.36 per acre respectively for navy, pinto and red kidney beans.

The results of inoculation were not convincing. However, there was some indication that the amount of nitrogen needed for optimum yield could be reduced if inoculation was used. If this observation is, in fact, accurate, this study should be continued for another year. This repeat would allow for a better evaluation of combinations of rate of applied N and seed inoculation for dry edible bean production.


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