Modeling the Effects of Nitrogen Fertilizer and Multiple Weed Interference on Soybean Yield

Understanding the effects of nitrogen (N) fertilizer on soybean-weed competition is essential for establishing a practical tool for N application and weed management. A two-year field experiment was conducted in a soybean field located in Bogatyrka (43.82 degrees N, 131.6 degrees E), Primorsky krai, Russia, to investigate the effects of N fertilizer and multiple-weed interference on soybean (Glycine max) yield and to model these effects. Soybean yield loss caused by the interference of multiple weeds including common ragweed (Ambrosia artemisiifolia), barnyard grass (Echinochloa crus-galli), and American slough grass (Beckmannia syzigachne) at different levels of N fertilizer was accurately described by a combined model incorporating inverse quadratic and exponential models into the rectangular hyperbolic model for two parameters Y-0 and beta, respectively. The combined model used in our study indicated that the application of N up to 36 kg N ha(-1) can increase weed-free soybean yield by 2.2 Mg ha(-1) but soybean yield under multiple-weed interference can sharply decrease with increasing total density equivalent, particularly at 36 kg N ha(-1). These results, including the combined model, thus can support decision making for weed management under different N uses in soybean cultivation.