Graduate Thesis Or Dissertation
 

Nitrate nitrogen accumulation and distribution in the soil profile during a fallow grain rotation as influenced by different levels of soil profile moisture

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  • The effect of different soil moisture levels on the amount and location of NO₃ -N accumulation in the soil profile were studied. The cultivars used in this study were Mcdermid, a soft white winter wheat, and Hudson, a medium early winter barley. Moisture treatments simulating dry, normal and wet fallow seasons were created by observing the actual precipitation pattern during the season and adjusting the accumulated averages to equal the calculated averages. Data were obtained for soil profile NO₃ -N, soil profile moisture, grain yield, spike per square meter, and 1000 kernel weight. The effects of fallow moisture levels on NO₃ -N accumulation in the soil profile were found significant. The highest NO₃ -N accumulation in the soil profile occurred under normal fallow moisture levels. At dry fallow moisture levels NO₃ -N accumulation was lowest. Higher levels of profile moisture adversely affected the NO₃ -N accumulation in the wet fallow plots. The 0-30 cm soil depth appeared to be an accumulation zone for NO₃ -N for all fallow moisture levels at the end of the fallow period. The effect of residual nitrate on NO₃ -N accumulation was highly significant in the spring of the fallow season. High residual nitrate of more than about 6 ppm in the soil profile suppressed NO₃ -N accumulation at each moisture level as compared to the initial levels. Grain yields were influenced by both nitrogen rate and fallow moisture levels. Increasing nitrogen rate to 56 kg/ha resulted in an increase in the grain yield at all moisture levels. Beyond 56 kg/ha nitrogen, all moisture treatments showed a decrease in grain yield. Fallow moisture levels did not influence 1000 kernel weight. Increased nitrogen rates significantly decreased 1000 kernel weight at each moisture level, except in the dry fallow plots. Increasing soil profile moisture resulted in an increase in spike number per square meter. Both cultivars produced more spikes /m² while nitrogen rate increased to 112 kg/ha at all moisture levels, except in the wet fallow plots with 112 kg/ha N. Cultivars showed highly significant difference in Water Use Efficiency. Hudson had higher W. U. E. (11.7 kg/ha-mm) than McDermid (9. 9 kg/ha-mm). There were no significant effects of the fallow moisture levels on W. U. E. ; however, the W. U. E. was increased significantly as the nitrogen rate increased to 56 kg/ha for both cultivars.
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