Potato yield and tuber set as affected by phosphorus fertilization

A 3 year field study on a loamy sand soil with medium to high soil test phosphorus (P) concentrations (25 to 33 mg kg^-1 Bray P1) was conducted to evaluate the effect of P fertilizer rate, source, and timing, and starter nitrogen (N) rate on potato (Solanum tuberosum L. cv. Russet Burbank) yield, tuber size, tuber set, petiole P concentration, and P uptake and distribution within the plant. Nine fertilizer treatments compared banded P rates of 0, 37, 42, and 74 kg P ha^-1, the P sources monoammonium phosphate (MAP) and diammonium phosphate (DAP), P banded at planting vs. split applications at planting and emergence, and starter N rates of 38 and 66 kg N ha^-1. Phosphorus fertilizer application increased total tuber yield and yield of undersized tubers (tubers less than 85 g), but decreased the proportion of large-sized tubers (greater than 285 g). Due to the increases in small, unmarketable tubers, P fertilizer application did not have a significant effect on marketable tuber yield (tubers greater than 85 g). The total number of tubers per plant and the number of undersized tubers were also higher, and the number of large tubers was lower, when P was applied compared with the zero P control. Both the number and yield of undersized tubers increased as P application rate increased. Petiole P concentrations were generally consistent with the rate of P applied, but they varied by year in magnitude and their pattern through the season. Petiole P was positively correlated with the number of tubers per plant, but only correlated for 1 year with differences in total yield. Phosphorus application increased total P uptake due primarily to an increase in tuber P concentration. Increases in total uptake and tuber P increased as P application rate increased, but differences in uptake were small relative to the amounts of P applied. Phosphorus source and timing and starter N rate did not consistently affect tuber yield, number, or size, petiole or tuber P concentration, and P uptake. The results of this study indicate that P nutrition can play an important role in regulating tuber set.