Yield and Nitrogen Recovery from Field-Grown Supernodulating Soybean

Abstract

Crop rotations that include soybean [Glycine max (L.) Merr.] increase yields and reduce N fertilizer requirements of subsequent nonlegume crops such as corn (Zea mays L.) or wheat (Triticum aestivum L.). Nitrogen from biological fixation is often given credit for this benefit. However, recent studies suggest that soybean may remove more N from the soil than it contributes. The availability of soybean lines capable of supernodulation may provide the opportunity to supply more N for subsequent crop use. The objectives of this research were to (i) determine the yield and growth characteristics of a soybean with supernodulation and (ii) to determine the influence of supernodulation on the yield and growth characteristics of winter wheat planted after soybean. Field studies were conducted for 3 yr (1993-1995) under rainfed conditions at Arlington, WI, on a Plano silt loam (fine-silty, mixed, mesic Typic Argiudoll) and under irrigated conditions at Hancock, WI on a Plainfield sandy loam (loamy-sand, mixed, mesic Typic Udipsamment). Four soybean genotypes were evaluated at R3, R7 and R8 growth stages included supernodulating, the normal nodulating parent of the supernodulating line, a nonnodulating line, and the normal nodulating parent of the nonnodulating line. The nonnodulating line provided a baseline of soybean performance without M 2 fixation capabilities. 'Merrimac' winter wheat planted after all soybean plots were harvested was evaluated at Z37, Z50, and Z90 growth stages. Depending on location, the supernodulating genotype increased soybean nodule density 43 to 135%, soil nitrate N at R3 growth stage 34 to 48% and biomass N 10 to 19% compared with the normal nodulating genotypes. However, at the R7 and R8 growth stages, soil nitrate N, plant biomass N and forage and grain yields were not different between the normal and supernodulating genotypes. Winter wheat grown after supernodulating soybean had no difference in soil nitrate N, biomass N, or forage or grain yield compared with normal nodulating genotypes. Based on these results, there does not appear to be any agronomic benefit to using tbese supernodulating soybean compared with normal nodulating lines.