Nitrogen Management in No‐Tillage Grain Sorghum Production: I. Rate and Time of Application

Grain sorghum [ Sorghum bicolor (L.) Moench] is grown in rotation with wheat ( Triticum aestivum L.) and soybean [ Glycine max (L.) Merr.] in the mid‐Atlantic. Sufficient data on N fertilization of sorghum are not available for this region. Our objective was to evaluate the influence of multi‐rate N fertilization on dryland sorghum. Treatments consisted of factorial combinations of four starter‐band N rates (11, 34, 56, and 78 kg N ha −1 ) and four sidedress N rates (0, 45, 90, and 134 kg N ha −1 ). A broadcast treatment of 67 kg N ha −1 at planting was also included. Starter‐band was applied 5 cm to the side and below the seed. Sidedress was applied 35 days after emergence at the eight‐leaf growth stage. Grain yield ranged from 1.7 to 11.9 Mg ha −1 over eight site‐years and was responsive and nonresponsive to N applications on four sites each. Nonresponsiveness was either due to high levels (>85 kg N ha −1 ) of residual soil mineral N, or severe water stress conditions. Our results indicate that production of sorghum on soils testing high in mineral N (50 kg N ha −1 in the surface 0.3 m) at planting should not receive any starter‐band N in conjunction with sidedress N application of 130 kg N ha −1 for optimum economic return to N fertilization. For soils testing low in mineral N, 40 kg N ha −1 starter‐band in conjunction with 130 kg N ha −1 sidedress N should optimize the sorghum yields in most situations.