ABSTRACTSeveral researchers have determined the effect of direct application of N to soybeans with conflicting results. This study was designed to allow measurement of the residual effects of repeated applications of fertilizer to previous corn crops on soybean yields. Treatments, including row spacings, plant populations, and rates of N and P for corn, were repeated from 1968 through 1972 on a Judson silt loam. Soil samples to a 180-cm depth were collected in the fall of 1972 and analyzed for NO3--N and acid-soluble P. Inoculated soybeans were then planted in 1973.Soybean yields were linearly related to the rate of N and P applied to corn, but row spacings and plant populations had no effect. Soybean yields were related to the acid-soluble P content of the surface soil (r = .438*), the NO3--N content of the surface soil (r = .983**), the NO3--N content of soil from 30–60 cm (r =.965**), and the total amount of NO3--N to 180 cm (r = .972**). The data from this study indicate that residual N and P resulting from prior fertilizer applications may influence soybean yields.
Several researchers have determined the effect of direct application of N to soybeans with conflicting results. This study was designed to allow measurement of the residual effects of repeated applications of fertilizer to previous corn crops on soybean yields. Treatments, including row spacings, plant populations, and rates of N and P for corn, were repeated from 1968 through 1972 on a Judson silt loam. Soil samples to a 180-cm depth were collected in the fall of 1972 and analyzed for NO3--N and acid-soluble P. Inoculated soybeans were then planted in 1973.
Soybean yields were linearly related to the rate of N and P applied to corn, but row spacings and plant populations had no effect. Soybean yields were related to the acid-soluble P content of the surface soil (r = .438*), the NO3--N content of the surface soil (r = .983**), the NO3--N content of soil from 30–60 cm (r =.965**), and the total amount of NO3--N to 180 cm (r = .972**). The data from this study indicate that residual N and P resulting from prior fertilizer applications may influence soybean yields.
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