Nitrogen Fertilizer Requirements of Potatoes Using Carefully Scheduled Sprinkler Irrigation

Abstract

Nitrogen fertilizer rates and timings were reexamined for potatoes (Solanum tuberosum L.) under sprinkler irrigation with scheduling by soil water potential. Four potato cultivars were grown on a silt loam soil in eastern Oregon in 1992, 1993, and 1994. Potatoes were submitted to six treatments: four N fertilizer rates (0, 135, 200, and 270 kg·ha-1) and two split application treatments (67 kg·ha-1 applied three times, and 40 kg·ha-1 applied five times). The crop was irrigated when the soil water potential at 0.2-m depth reached -60 J·kg-1. No more than the accumulated evapotranspiration was replaced at each irrigation. Over 3 years, the cultivars had similar responses to N rates and N timing. In 1992, following alfalfa, tuber yield was not responsive to N fertilization. In 1993 and 1994, following wheat, tuber yield was maximized by N at 211 and 175 kg·ha-1. Split applications of the N fertilizer did not increase tuber yield in any year. In 1993 and 1994, the highest tuber specific gravity was obtained with no N fertilization. Nitrogen rates above the optimum resulted in darker frying tubers in 1992 and 1993. The N rates maximizing tuber yield in this study were lower than the rates recommended in the university fertilizer guides.