Influence of fertilizer,irrigation, and storage treatments on nitrate-N content of potato tubers

A survey was undertaken to investigate the nitrate-nitrogen (NO₃-N) content of potatoes grown on different soil types with different fertilizer and irrigation treatments. Tuber nitrate-N contents were determined immediately after harvest and after periods of storage of up to 210 days. Nitrate-N in tubers (dry weight basis) ranged from low values of 82 to 122 ppm for low nitrogen fertility levels to a maximum of 192 to 285 ppm at the highest nitrogen rates, where irrigation was applied at optimum levels. The average nitrate-N in tubers under such conditions was 150 to 160 ppm. Where irrigation management was less than optimum, the nitrate-N content of tubers increased, reaching an average maximum value of 786 ppm at the highest fertilizer rate. The study showed that the nitrate-N level in tubers increased with nitrogen fertilization rates, although there was not a linear relationship between N fertilizer rate and tuber nitrate-N. The highest nitrate-N levels obtained in the tubers under proper irrigation management, even with 800 lb N/A, did not exceed 300 ppm nitrate-N and were usually less than 200 ppm. Data collected from this study suggest that improper irrigation, especially with high nitrogen fertilizer rates, results in a dramatic increase in nitrate-N level in the tubers. Some individual tubers contained over 1200 ppm nitrate-N. There was an apparent slight increase in nitrate-N in the tubers with storage, although this increase was not consistent.