Rate and timing of nitrogen fertilizer application on potato 'FL1867' part II: Marketable yield and tuber quality

Optimum nitrogen fertilizer management is necessary to maintain sustainable and economical potato (Solanum tuberosum) production. The objective of this study was to determine the effect of N-fertilizer rate and timing of application on plant biomass, tuber marketable yield and quality of chipping potato irrigated by subirrigation. This study was conducted with grower collaboration on three farms for two consecutive years (2011 and 2012). All experimental plots received 56 kg ha−1 of N as ammonium nitrate approximately 40 days before planting, a common grower practice. Nitrogen fertilizer treatments were 0, 56, 112 or 168 kg ha−1 applied at plant emergence (Nemerg) combined with 56 or 112 kg ha−1 of N applied as a sidedress at tuber initiation (Ntuber init). The two years of this study were characterized by low rainfall conditions, reducing the risk of N leaching and runoff. Under these conditions, the N treatments rarely increased potato aboveground biomass. Mean marketable tuber yield across all sites ranged from 19.2 to 39.7 Mg ha−1 with the lowest yield when a large amount of rainfall occurred prior to harvest at one site. Marketable yield responded quadratically to increase N-fertilizer rates applied at plant emergence, with optimum yield calculated at Nemerg rate between 88 and 113 kg ha−1. Applying more than 56 kg ha−1 of N at tuber initiation did not increase marketable yield, tuber specific gravity or tuber quality on any farm in either year. Nitrogen rate treatments above 112 kg ha−1 at emergence, and 56 kg ha−1 at tuber initiation did not improve potato marketable yield or tuber quality. The contribution of 56 kg ha−1 applied at pre-plant to potato yield is still unknown, and may be more beneficial to move this application closer to planting.