Rotation and Fertilization Effects on Corn and Soybean Yields and Soybean Cyst Nematode Populations in a No-Tillage System

Rotations have long been used to improve crop yields. No-tillage production acreage is increasing, and production information on rotation effects on yields and soybean cyst nematode populations is needed for this system. Field experiments were initiated in 1985 and continued through 1992 to evaluate P-K fertilization effects on yield of a corn-soybean [Zea mays L.-Glycine max (L.) Merr.] rotation and on populations of soybean cyst nematode (Heterodera glycines Ichinohe) (SCN). The research was conducted on a Loring silt loam soil (a fine-silty, mixed, active, thermic Oxyaquic Fragiudalf), using no-tillage management. The experimental design was a split-plot for corn evaluation and split-split-plot for soybean evaluation. Individual treatments were replicated five times. Main plots were broadcast P-K rates of 0–0, 15–28, 29–56, 44–84, and 59–112 kg ha⁻¹. The split-plots were continuous corn, continuous soybean, a corn-soybean rotation, and a soybean-corn rotation. The split-split-plots were two soybean cultivars possessing different levels of SCN resistance. Yields of both crops were increased by the fertilization. In this study, corn yields were increased 14% and soybean yields increased 11% with the rotation. Rotating the two cultivars produced similar yields and nonrotated yields of resistant TN 4-86 were higher than susceptible Essex, indicating an effect of SCN. The primary benefit of corn in the rotation was to reduce SCN populations. However, within Essex rotations the SCN population recovery was rapid, while populations remained relatively low in the TN 4-86 rotations. The SCN populations were greater when rotations were fertilized with the two lowest P-K rates, compared with populations within the unfertilized check and the highest P-K rate. Soybean producers should consider a no-tillage system of rotatingcorn with SCN-resistant soybean cultivars, fertilized at high P and K rates for yield improvement and reduced SCN populations.