Effect of Nitrapyrin on N Response of Corn on Sandy Soils

Preplant N fertilizer applications on sandy Coastal Plain soils are often less efficient than sidedress N applications due to leaching of NO⁻₃ from the rhizosphere. Preplant-incorporated broadcast applications of ammoniacal N fertilizers containing the nitrification inhibitor nitrapyrin [2-chloro-6(trichloromethyl)pyridine] should increase utilization of the exchange capacity of sandy soils to retain NH⁺₄ and increase preplant N fertilizer efficiency. The effects of N rate, N source, and nitrapyrin on inorganic soil N form, soil N content, and corn (Zea mays L.) growth were investigated in 1977 on a Marlboro sand (Typic Paleudult) and a Varina loamy sand (Plinthic Paleudult) and in 1978 on a Wagram sand (Arenic Paleudult). Nitrogen treatments consisted of a zero-N check, preplant broadcast applications of 56, 112, 168, and 224 kg N/ha as urea, 112 kg N/ha as NaNO₃, and 112 kg N/ha as urea plus 1.12 kg nitrapyrin/ha dissolved in water. Soil N measurements at 34, 40, and 48 days after N treatment application on the Marlboro, Varina and Wagram soils, respectively, showed that nitrification was suppressed by nitrapyrin. The lack of significant differences in inorganic soil N contents in the 0 to 15 cm depth among 112 kg N/ha supplied as urea with and without nitrapyrin and NaN0₃ indicated that little leaching occurred in 1977. Leaching conditions in 1978 resulted in large losses of inorganic N from the rooting zone; however, when nitrapyrin was added with urea, losses of N were significantly reduced. High N rates from urea decreased the pH in all soils except when nitrapyrin was included. In 1977, inclusion of nitrapyrin with urea had little effect on leaf N, grain yields, plant N accumulation or N fertilizer recovery due to small losses of soil inorganic N. However, in 1978 when leaching conditions occurred, nitrapyrin with urea decreased soil N losses, significantly increased leaf N concentration, grain yields, plant N accumulation and N fertilizer recovery.