Nitrates in soil after long‐term management for dryland grain sorghum and winter wheat

Abstract

Long‐term cropping with clean and stubble mulch tillage (SMT) resulted in soil organic carbon and total nitrogen (N) decreases at numerous Great Plains locations. Crops at some locations now respond to applied ? fertilizers. Objective of this study was to compare soil nitrate‐N (NO3‐N) contents after a 12‐year field study for which different management practices [cropping systems (rotations or continual cropping), tillage methods (SMT or no‐tillage), land leveling (level or nonlevel), and ? fertilizer (applied or not applied)] were used for dryland grain sorghum [Sorghum bicolor (L.) Moench] and winter wheat (Triticum aestivum L.) production. Pullman clay loam (fine, mixed, superactive, thermic Torrertic Paleustoll) was sampled by increments to a 20‐cm depth. Relatively few differences in NO3‐N contents due cropping system, land leveling, or tillage treatments were significant for individual depths or means across all depths. Cropping systems had no effect, but contents were greater in wheat than in sorghum or fallow plots. Land leveling and tillage methods resulted in no consistent differences, but contents usually were greater with than without applied fertilizer. Although ? fertilizer treatments were imposed early in the field study because plant ? deficiencies symptoms were noted, crops did not respond to applied fertilizer. This suggests the NO3‐N content differences found will have little effect on dryland crop yields under present management conditions.