Nitrate Concentration in Potato Petioles from Periodic Applications of 15N-Labeled Ammonium Nitrate Fertilizer
- S. Roberts ,
- H. H. Cheng and
- F. O. Farrow
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 15NO3-N in petioles of Russet Burbank potato (Solanum tuberosum L.) following periodic treatments of 15N-labeled NH4NO3 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 NH4NO3 split into starter and supplemental applications. Split plot treatments consisted of labeling the NH4NO3 with 15N at various times. Results indicate that supplements of 15NH4 15NO3 were taken up by the plants and concentrated in petioles within 1 wk after application at various times throughout the growing season. The 15N from pre-emergence starter fertilizer applied in May was evident in petiole NO3 at each petiole sampling through the entire season. Uptake of the 15NO3 source reached a higher peak in petioles 1 wk to 10 d ahead of 15NO3 that was nitrified and taken up from applying the same rate of labeled 15NH4 source. The uptake of labeled NH4 in petioles was not determined. These data suggest that monitored petiole NO3 values could underestimate the soil N available from NH4 fertilization. These results with 15N tracer indicate that the process of N uptake is a dynamic one which continues as long as plants are active throughout the growing season.
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