One question that researchers and producers are both asking is: Do high yielding soybeans need to be fertilized with N? Soybeans require a substantial amount of N, 4 to 5 lbs. per bushel of grain. Biological N fixation (BNF) can only supply from 40 to 70% of what is required with the rest of the N coming from the soil. As growers produce more soybeans in the 70 and 80 bu/acre range, or the environment becomes more stressful, both BNF and soil reserves may not be able to supply enough N and could become limiting, thus the potential for supplemental N response will become more common.
Responses from applied N are inconsistent and unpredictable. This unpredictability of when, why, and where an N response will occur needs to be understood and the variance in BNF is a contributor to that unpredictability. A better understanding of the N balance for soybean is needed in order to sustainably increase production and seed quality, maximize profits, increase the efficiency in the use of inputs and reduce the environmental footprint of current food production systems.
South Dakota has been invited to participate in a national soybean research effort examining biological N fixation with ten participating universities (Ignacio Ciampitti, Kansas State University; and Seth Naeve, University of Minnesota; Lead PIs).
Biological Nitrogen Fixation may be the most important economic and environmental process affecting crop production (and certainly soybean production) in the United States, yet it is only partially characterized. We know surprisingly little about the quantities of N fixed by US soybean crops or the fate of that N in the environment. A better understanding of the soil, soybean management, and environmental factors affecting BNF along with the quantities of N fixed will contribute to scientific knowledge leading to greater soybean yields, higher soybean quality, lower environmental impacts, and greater returns to US farmers. We propose to perform two trial locations in South Dakota for this study, one likely to be responsive to S fertilizers and one likely to be unresponsive.