Author
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Unger, Paul |
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Submitted to: Communications in Soil Science and Plant Analysis
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 2/14/2000 Publication Date: N/A Citation: N/A Interpretive Summary: Organic carbon and total nitrogen (N) in soil decreased greatly in the Great Plains where clean and stubble mulch tillage were used for crop production for a long time. Crops now respond to applied N fertilizers at some locations. This study was conducted to compare soil nitrate-N contents where different management practices were used for dryland grain sorghum and winter wheat production for 12 years in a field study. Practices compared were cropping systems (rotations or continual cropping), tillage methods (stubble mulch or no-tillage), land leveling (level or nonlevel), and N fertilizer use (applied or not applied). The soil (Pullman clay loam) was sampled at three increments to a 20-cm depth. Relatively few nitrate-N content differences due to cropping system, land leveling, or tillage treatments were significant for individual depths or for the totals for the 20-cm depth. For wheat or sorghum crops individually, 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 N fertilizer was applied for the wheat and sorghum early in the field study because plant N deficiencies symptoms were noted, crop grain yields were not increased when N fertilizer was applied. This suggests the nitrate-N content differences that were found will have little effect on dryland crop yields under present management conditions. Technical Abstract: Long-term cropping with clean and stubble mulch tillage (SMT) resulted in soil organic carbon and total nitrogen decreases at numerous Great Plains locations. Crops at some locations now respond to applied N 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 N 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 to 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 N fertilizer treatments were imposed early in the field study because plant N 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. |
