Impact of Inoculation and Use of Fertilizer Nitrogen on Soybean Production Where Growing Seasons Are Short

Twelve field experiments were conducted in northwest Minnesota from 1984 through 1987 to evaluate the effects of inoculation and fertilizer N on soybean ( Glycine max L.) production on a variety of soils. Twelve locations having a range of soil NO 3 ‐N contents from 22 to 164 lb/acre in the 0 to 2‐ft depth were selected. ‘McCall’ soybeans were planted at each location. Two inoculation levels (none and 2 × recommended) were combined with five N rates (0, 30, 60, 90, and 120 lb N/acre) supplied as urea (46‐0‐0). Nitrogen was broadcast and incorporated before planting. Inoculum did not increase yield at 10 of 12 locations. Grain yield response to N fertilizer was strongly related to soil NO 3 ‐N content. When the NO 3 ‐N content was greater than 80 lb/acre (0–2 ft) there was no response to applied N. Trifoliate leaf N contents may be useful for determination of N deficiency in soybeans.