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Twelve Years of Continuous Corn Fertilization with Ammonium Nitrate or Urea Nitrogen¹

ABSTRACT

Field studies on a Webster loam (pH 6.8) compared ammonium nitrate N to urea N for corn (Zea mays L.). The comparison included N removal, grain yield, use as an annual fall plowdown and late June sidedressing, and use on fall-plowed and spring surfaces. Rates of N broadcast were 45, 90, and 180 kg/ha. Starter fertilizer on all treatments supplied an additional 16 kg N, 21 kg of P, and 20 kg of K/ha (1975 lbs. of 8-24-12/acre). The two N sources produced equivalent average yield increases in seven of the eight comparisons, but sidedressed urea N was significantly superior to the NH₄NO₃ when both were broadcast at the 90 kg rate. Both N sources broadcast on fall plowing were equally effective to similar treatments plowed down. Increasing N application rates significantly increased corn production and N removal, but only the highest N application rate (196 kg N/ha annually) materially increased NO₃-N concentrations in the soil. None of the N treatments increased soil NO₃-N concentrations beyond the 2-m depth, and it is assumed that excess NO₃-N to this soil depth was largely removed in the tile drainage waters.

¹ Contribution from Dep. of Soil Sci., Univ. of Minnesota at St. Paul 55101. Presented before Div. S-4, Soil Sci. Soc. of Amer. at Miami, Fla., Oct. 31, 1972. Paper no. 8180 of the Scientific Journal Series, Minnesota Agr. Exp. Sta., Univ. of Minnesota, St. Paul.

² Professor and Superintendent of the Southwestern Minnesota Exp. Sta. and Professor of Soil Science, respectively.

Received for publication January 2, 1973. Accepted for publication April 3, 1973.