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N-Source and Irrigation Effects on Nitrate Leaching¹

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 NO₃-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(N0₃)₂, (NH₄)₂SO₄, and CO(NH₃)₂, and a check treatment were compared in factorial combination with two irrigation levels. Nitrate and NH₄+-N concentrations in leachate were measured throughout the study. Total-N and NO₃--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 NH₄+-N or N0₃--N. Maximum depth of NO₂-- N leaching, which was approximately 60 cm, occurred with Ca(N0₃)₂ and high volume-low frequency irrigations. No N0₃--N accumulated below 20 cm when (NH₄)₂SO₄, and CO(NH₂)₂ were applied, followed by low volume-high frequency irrigations. Total amount and depth of N0₃-₃-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 N0₃--N leaching was generally CO(NH₂)₂ check<(NH₄)₂S0₄<Ca(N0₃)₂, although N0₂--N leaching from urea treatments may have been offset by ammonia volatilization following treatment applications. Nitrate leaching from N fertilizers under irrigation may be minimized by timely applications of ammonia based fertilizers and low volume irrigations to minimize leaching below the crop root zone.

Key Words: Mass flow • Irrigation management • Fertilizer management • Percolation • Hydrolysis • Mineralization

² Former assistant professor, and technician, Dep. of Soils, North Dakota State Univ., Fargo, ND 58105. Senior author is now assistant professor, Dep. of Soil Sci., Univ. of Minnesota, St. Paul, hfN 55108

Received for publication July 13, 1979.