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 produ ction acreage is increasing, and production information on rotation ef fects on yields and soybean cyst nematode populations is needed for th is system. Field experiments were initiated in 1985 and continued thro ugh 1992 to evaluate P-K fertilization effects on yield of a corn-soyb ean [Zea mays L.-Glycine max (L.) Merr,] rotation and on populations o f soybean cyst nematode (Heterodera glycines Ichinohe) (SCN), The rese arch was conducted on a Loring silt loam soil (a fine-silty, mixed, ac tive, thermic Oxyaquic Fragiudalf), using no-tillage management. The e xperimental design was a split-plot for corn evaluation and split-spli t-plot for soybean evaluation, Individual treatments were replicated f ive times, Main plots were broadcast P-K rates of 0-0, 15-28, 29-56, 4 4-84, and 59-112 kg ha(-1). The split-plots were continuous corn, cont inuous 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 f ertilization, In this study, corn yields were increased 14% and soybea n yields increased 11% with the rotation. Rotating the two cultivars p roduced similar yields and nonrotated yields of resistant TN 4-86 were higher than susceptible Essex, indicating an effect of SCN, The prima ry benefit of corn in the rotation was to reduce SCN populations. Howe ver, within Essex rotations the SCN population recovery was rapid, whi le populations remained relatively low in the TN 4-86 rotations, The S CN populations were greater when rotations were fertilized with the tw o 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 rotating corn with SCN-resistant soybean cultivars, fertilized at high P and K rates for yield improvement and reduced SC N populations.