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

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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.

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