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 mar (L.) Merr.] in the mid-Atl antic Sufficient data on N fertilization of sorghum are not available for t his region. Our objective was to evaluate the influence of multi-rate N fer tilization on dryland sorghum. Treatments consisted of factorial combinatio ns of four starter-band N rates (11, 34, 56, and 78 kg N ha(-1)) and four s idedress 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 c m to the side and below the seed. Sidedress was applied 35 days after emerg ence 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 app lications on four sites each. Nonresponsiveness was either due to high leve ls (>85 kg N ha(-1)) of residual soil mineral N, or severe water stress con ditions. Our results indicate that production of sorghum on soils testing h igh in mineral N (50 kg N ha(-1) in the surface 0.3 m) at planting should n ot receive any starter-band N in conjunction with sidedress N application o f 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 situ ations.