Nitrogen source evaluation for potato production on irrigated sandy soils

Ammonium sulfate (AS), ammonium nitrate (AN), urea (U), and calcium nitrate (CN) were evaluated as supplemental N sources for sprinkler irrigated potatoes on a loamy sand soil by determining N source effects on potato yield, quality, recovery of applied N in tubers, and petiole NO ₃ ^- concentration. At the N rate required to maximize yield (224 kg N/ha), 5-year average yields obtained with AS were significantly higher than those obtained using AN, U, or CN. Average total tuber yields with AS, AN, U, and CN were 59.3, 56.2, 56.5, and 54.8 Mg/ha, respectively. Yield differences between AS and AN or CN are likely due to greater N loss through leaching from the NO ₃ ^- -containing sources. This conclusion is supported by lower petiole NO ₃ ^- concentrations and lower recovery of applied N in tubers when AN or CN were used. Yield differences between AS and U suggest that N applied as U is more susceptible to loss than N applied as AS on the soil used in this work. The percentage of total tuber yield in the US1A quality category was not affected by N source, but the percentage of cull tubers was higher with AS than with AN or CN. Our results indicate that potato yield and N recovery can be improved by use of AS instead of U, AN, or CN for irrigated potato production on sandy soils. Potato yield, quality, and N recovery were similar when U or AN were used as supplemental N sources.