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.