N-Fertilizer Use Efficiency of Split-Application for Potato.

Optimal timing of split-fertilizer applications is imperative to increase N-fertilizer use and reduce losses to the environment. For potato in northeastern Florida N-fertilizer is commonly applied at fumigation 30 days before planting, at plant emergence and at tuber initiation. The objective of this study was to compare the N-fertilizer use efficiency (NFUE) of potato for each fertilizer application timing for two commercial potato varieties ‘Atlantic’ and ‘FL1867’. Field experiments were conducted in Hastings, FL in spring 2013. The NFUE was evaluated by the substitution of conventional N-fertilizer by enriched ¹⁵N ammonium nitrate. Potatoes received 224 kg/ha N evenly split into three doses. Labeled fertilizer was applied to microplots at one of the three fertilization events, with un-labeled fertilizer used for the remaining application events. Yield, total N and ratio of ¹⁵N/¹⁴N in the soil, potato plant, and weeds was quantified and the NFUE of each fertilizer application was determined. There was no difference in yield between varieties with the average yield being 36.6 Mg/ha and total plant biomass and N accumulation averaged 10,500 and 142 kg ha^-1 respectively. Potato NFUE was 7%, 45% and 48% for the pre-plant, emergence, and sidedress applications respectively. Residual soil N accounted for less than 1% of applied N fertilizer. Unaccounted N-fertilizer was 93%, 54%, and 51% of the applied fertilizer at pre-plant, emergence, and sidedress applications respectively.