Commercial Evaluation of Seasonal Distribution of Nitrogen Fertilizer for Potato

The timing of nitrogen (N) fertilizer application has a direct impact on fertilizer use efficiency of potato (Solanum tuberosum L.) and nitrate leaching. The objective of this study was to determine the effect of N fertilizer rate combined with application timing on soil mineral N availability, tuber yield and quality of crisp potato in northeast Florida. Trials were performed on three commercial farms in 2011 and repeated on two farms in 2012. N fertilizer was applied at three different timings: at pre-plant (Npre-pl), at plant emergence (N-emerg) and at tuber initiation (N-tuber init). All seven treatments received a total of 224 kg ha(-1) of N, with each treatment differing in the proportion of N supplied at each application timing. N was applied at 0 or 56 kg ha(-1) at Npre-pl followed by 0, 56, 112 or 168 kg ha(-1) of N applied at N-emerg and 0, 56, 112 or 168 kg ha(-1) of N applied at N-tuber init. Treatments were combined in fractional factorial arrangement in a randomized block design with four replicates. Tuber marketable yield ranged from 23.7 to 44.6 Mg ha(-1). Total and marketable yields were unaffected by timing or N rate combinations on two out of three farms and tuber quality was mostly unaffected by application timing. Higher yields were obtained when 56 kg ha(-1) of N was supplied at pre-plant compared to 0 kg ha(-1) of N on only one farm in both years. On the same farm, regardless of the application of 0 or 56 kg ha(-1) Npre-pl, the application of 168 kg ha(-1) of N-emerg resulted in superior total yields than when 168 kg ha(-1) was instead supplied later in the season at N-tuber init. Higher proportions of N at pre-plant and tuber initiation tended to decrease potato tuber size, and a high proportion of N supplied at tuber initiation resulted in lower yield and higher residual soil mineral N at the end of the season.