Petiole and soil nitrogen concentrations during the growing season of two potato cultivars as influenced by different nitrogen-management practices

Fine-tuning potato nitrogen (N) management for irrigated sandy soils is a desirable goal to optimize the production and minimize negative impacts on the environment. Effects of different rates of preplant N (PP-N) applications and different rates and frequencies of in-season N (IS-N) for two potato cultivars were evaluated for 2 years (2001 and 2002) in a Quincy fine sand (mixed, mesic, Xeric Torripsamments) in the Pacific Northwest (PNW). in the 2001 experiment, the petiole nitrate (NO3-N) concentrations in both the cultivars were in the optimum range in the samples taken 22 days after emergence (DAE). In the subsequent sampling, the petiole NO3-N concentrations showed a wide range proportional to the rates of IS-N. In the 2002 experiment, the petiole NO3-N concentrations were in the excess range in most treatments until about 51 DAE in both the cultivars, followed by a decline in concentrations to the low range. The petiole phosphorus (P) and potassium (K) concentrations were mostly above the excess range in both the cultivars over the entire sampling period. The soil N data showed that the transformation of urea N was quite rapid and that the extractable ammonium (NH4-N) and NO3-N concentrations in the soil returned to the background levels within 90 days after the PP-N application. The results of this study demonstrate a rapid transformation of preplant applied urea N into NH4-N and NO3-N and depletion of the available N in the top 120 cm of soil. This, in turn, supports the need for IS-N applications to meet the crop N requirement during the later growing period.