Evaluation of Nitrapyrin as a Means of Improving N Efficiency in Irrigated Sands1

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Abstract
The efficiency of fertilizer N is usually low when potatoes (Solanum tuberosum L.) are grown on irrigated sands, because of rapid leaching of NO3. The objective of this research was to determine if optimum levels of N might be maintained throughout the growing season by delaying nitrification with a nitrification inhibitor, Nitrapyrin [2‐chloro‐6‐(trichloromethyl)pyridine] (NI). This method would increase fertilizer N efficiency and also reduce the potential for groundwater contamination. Several field experiments were conducted on a Plainfield loamy sand (Typic Udipsamment; sandy, mixed, mesic) involving various N sources, rates, and times of application with and without NI. Potato tuber yield and the forms and distribution of N in and below the fertilizer bands were determined. Nitrapyrin extended the persistence of applied NH4 in all experiments, but inhibition of nitrification was of relatively short duration. Nitrapyrin persistence was likely reduced by the more rapid volatilization and hydrolysis in sandy soils. Further, the effectiveness of NI was likely limited by rapid leaching of NH4 out of the NI‐treated zone. Application of NI reduced both total tuber yield and the proportion of marketable tubers. The greatest reductions were found on treatments receiving NI both at planting and at sidedress. The soil sampling data showed that NI maintained a much higher NH4‐N/NO3‐N ratio than comparable non‐NI treatments. It appears that the predominance of NH4‐N interfered with plant metabolism so that both yield and normal development of tubers were impaired.