Nitrate Concentration in Potato Petioles from Periodic Applications of ¹⁵N‐Labeled Ammonium Nitrate Fertilizer

Abstract

Abstract Concerns for N use efficiency prompted a tracer study of the effectiveness of applying supplemental N fertilizer throughout the growing season. The purpose of the study was to monitor the concentration of 15 NO 3 ‐N in petioles of Russet Burbank potato ( Solanum tuberosum L.) following periodic treatments of 15 N‐labeled NH 4 NO 3 on Quincy loamy sand (mixed, mesic Xeric Torripsamments). The experiments were conducted for 5 yr with main plot N rates of 224, 336, and 560 kg ha −1 as NH 4 NO 3 split into starter and supplemental applications. Split plot treatments consisted of labeling the NH 4 NO 3 with 15 N at various times. Results indicate that supplements of 15 NH 4 15 NO 3 were taken up by the plants and concentrated in petioles within 1 wk after application at various times throughout the growing season. The 15 N from pre‐emergence starter fertilizer applied in May was evident in petiole NO 3 at each petiole sampling through the entire season. Uptake of the 15 NO 3 source reached a higher peak in petioles 1 wk to 10 d ahead of 15 NO 3 that was nitrified and taken up from applying the same rate of labeled 15 NH 4 source. The uptake of labeled NH 4 in petioles was not determined. These data suggest that monitored petiole NO 3 values could underestimate the soil N available from NH 4 fertilization. These results with 15 N tracer indicate that the process of N uptake is a dynamic one which continues as long as plants are active throughout the growing season.