N‐Source and Irrigation Effects on Nitrate Leaching 1

Efficiency of N fertilizer sources and N leaching below the root zone of irrigated crops are concerns of agronomists and environmentalists alike. Practical data comparing the efficacy and leaching susceptibility of various N sources are necessary for resource management and as input to current nutrient transport models. This study was conducted to evaluate the effects of N fertilizer source and irrigation management on distribution of N and on leaching of NO 3 − ‐N within the root zone of a small‐grain crop. Undisturbed columns of Maddock fine sandy loam, a well‐drained Udorthentic Haploboroll, were ciopped to wheat ( Triticum aestivum L. cv. 'Era') in a greenhouse study. Three N source, Ca(NO 3 ) 2 , (NH 4 ) 2 SO 4 , and CO(NH 3 ) 2 , and a check treatment were compared in factorial combination with two irrigation levels. Nitrate and NH 4 +‐N concentrations in leachate were measured throughout the study. Total‐N and NO 3 − ‐N in the soil columns were measured at harvest. Percolation from the columns was the same for all treatments. Essentially, none of the applied N leached below the rooting depth as either NH 4 +‐N or NO 3 − ‐N. Maximum depth of NO 3 − ‐N leaching, which was approximately 60 cm, occurred with Ca(NO 3 ) 2 and high volume‐low frequency irrigations. No NO 3 − ‐N accumulated below 20 cm when (NH 4 ) 2 SO 4 , and CO(NH 2 ) 2 were applied, followed by low volume‐high frequency irrigations. Total amount and depth of NO 3 − ‐ 3 ‐N leached were dependent on irrigation method and N source. High volume‐low frequency irrigations leached solutes to a greater depth than did low volume‐high frequency irrigations. Contribution of N source to NO 3 − ‐N leaching was generally CO(NH 2 ) 2 ≤ check<(NH 4 ) 2 S0 4

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