Yield, market quality and petiole nitrate concentration of non-irrigated Russet Burbank and Shepody potatoes in response to sidedressed nitrogen

Russet Burbank and Shepody potatoes were grown with the following four nitrogen treatments: 1) 90 kg ha−1 at planting; 2) 180 kg ha−1 at planting; 3) 90 kg ha−1 at planting followed by an additional 90 kg ha−1 side-dressed after tuber initiation; or 4) 90 kg ha−1 at planting followed by an additional 45 kg ha−1 sidedressing. When compared to the 90 kg ha−1 at-planting treatment, petiole NO3-N concentrations increased rapidly after sidedressing and were relatively constant through mid-season. Sidedressed N significantly increased total yields relative to the 90 kg N ha−1 at-planting treatment by an average of 5.0 t ha−1 in three of nine experiments. Three of the experiments, where yields did not significantly increase, were on sites which were not expected to respond to supplemental N based on petiole NO3-N testing. A red clover green manure crop was the previous crop for two of these experimental sites. Petiole NO3-N testing criteria were only partially effective in detecting sites where response to sidedressed N occurred. When compared to a single application of 180 kg N ha−1 at planting, split application of 90 kg N ha−1 at planting followed by a 90 kg N ha−1 sidedressing significantly reduced total yields in one of nine experiments and did not affect yields in the remaining eight experiments. Tuber uniformity was improved in three of nine experiments by the split-N treatment. Specific gravity was not significantly affected. Use of 45 kg N ha−1 at side-dressing resulted in similar yield as the 90 kg N ha−1 sidedressing, although yield of large-sized tubers was often decreased with the lower N rate.