Reduced Nitrogen Fertilization Requirements of Potatoes under Precision Irrigation
Seven potato cultivars were grown on silt loam with six N fertilizer treatments in 1992, 1993, and 1994 to evaluate varietal response to N fertilizer rate and timing under precision sprinkler irrigation. Crop evapotranspiration was replaced when the soil water potential at 0.2-m depth reached –60 kPa. Maximum yield responses were obtained using 0 to 134 kg N/ha, depending on the year and experimental site. In 1993 and 1994, with wheat as the previous crop, 134 kg N/ha maximized yields, over all varieties. In 1992, with alfalfa as the previous crop, there was no positive yield or grade response to N, over all varieties. Each year, available soil N accounting showed large surpluses for all treatments. Nitrogen mineralization contributed from 80 to 280 kg N/ha per year to the soil supply.