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Guidelines for N fertilizer management of potato (Solanum tuberosum L.) that include application timing and rates are fundamental to minimize yield reduction risks. The study objectives were to determine the effect of N fertilizer rate, applied at the plant emergence and tuber initiation stages, on N use efficiency and yield of cultivar Atlantic chipping potato. Fertilizer rates of 0, 56, 112, 168 kg ha -1 were applied at plant emergence, and 56 and 112 kg ha -1 were applied at tuber initiation as a side-dress in a factorial randomized complete block design with four replicates in three consecutive years at three commercial farms. All treatments received 56 kg ha -1 of N at pre-plant. Total N fertilizer applied ranged from 112 to 370 kg ha -1 . Applied N rates influenced the levels of soil inorganic N. The maximum daily N uptake occurred between 55 and 70 d after planting, coinciding with the onset of the tuber bulking stage. Potato yield was similar between N rates applied at emergence with the exception of one farm in 2010 due to high precipitation. Average tuber yield ranged from 15 to 33, 29 to 41, and 33 to 39 Mg ha -1 in 2010, 2011, and 2012, respectively. Tuber yield and plant N uptake were similar with N rates above 56 kg ha -1 applied-at tuber initiation. There was an increased residual concentration of soil N at harvest with higher N application; however, this did not correlate to an increase in potato yield. ).Abbreviations: DAP, days after planting; GDD, growing degree days; N emerg. , nitrogen fertilizer applied at plant emergence 16 to 29 days after planting; NHI, nitrogen harvest index; N pre-pl. , N fertilizer applied at pre-plant 34 to 44 days before planting; N tuber init. , nitrogen fertilizer application as side-dress at tuber initiation, 41 to 51 days after planting; NUE, nitrogen use efficiency; NUpE, nitrogen uptake efficiency; NUtE, nitrogen utilization efficiency.

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