Rate and timing of nitrogen fertilizer application on potato 'FL1867'. Part I: Plant nitrogen uptake and soil nitrogen availability

Knowledge of seasonal nutrient demand is necessary to maximize potato (Solanum tuberosum) yield and profitability while also minimizing the risk of excess fertilizer leaching into waterways. The objective of this study was to determine the effect of the N fertilizer rate and timing of application on the N use efficiency (NUE) and yield of chipping potato 'FL1867'. This study was conducted with grower collaboration on three commercial farms for two years (2011 and 2012) using subirrigation on course textured soils in Florida. All treatments received 56 kg ha−1 of N as ammonium nitrate applied as a band approximately 40 days before planting (Npre-pl). Liquid urea ammonium nitrate was then band applied at 0, 56, 112, or 168 kg ha−1 at plant emergence (Nemerg) followed by 56 or 112 kg ha−1 applied as a side-dress at tuber initiation stage (Ntuber init). The treatments were arranged in a factorial design with four replicates. The total amount of N fertilizer applied ranged from 112 to 336 kg ha−1. Maximum daily N uptake by the potato crop occurred between 55 and 65 days after planting, coinciding with the onset of the tuber bulking stage. Heavy rainfall prior to planting the 2011 crop reduced soil N availability from pre-plant applied N fertilizer indicating the high susceptibility of that application timing to leaching. Average tuber yield ranged from 25.6 to 47.2 Mg ha −1, with the lowest yields occurring when heavy rainfall close to harvest increased yield loss to decay. While higher Nemerg rates increased soil inorganic N, tuber yield was either not affected by N application or responded quadratically peaking at Nemerg levels between 95 and 125 kg ha−1. N application rates above this range decreased yield and NUE while increasing soil residual N at the end of the season. Plant N uptake and tuber yield did not increase with Ntuber init rate above 56 kg ha−1 and it was associated with lower NUE and also higher residual soil N.