Nitrogen, Chloride, and Water Balance with Irrigated Russet Burbank Potatoes in a Sandy Soil1

Abstract

AbstractLarge applications of sprinkler irrigation and N fertilizer have been implicated in causing nitrate contamination of ground water in central Wisconsin.Field and lysimeter experiments were established in 1972 and 1973 on the Plainfield loamy sand to determine the effect of reducing the amount of sprinkler‐irrigation and fertilizer N on potato (Solanum tuberosum L., var. ‘Russet Burbank’) tuber yields and on the field water and N balance. Two main treatments were used. The conventional (CON) treatment received irrigation water and N fertilizer according to current recommendations. The improved (IMP) treatment received less irrigation water than the CON treatment in both years. In both years fertilizer N was applied more frequently to the IMP treatment and in 1973 the total amount applied was less in the IMP treatment than in the CON treatment. Chloride (as KCl) accompanied N on a one‐to‐one weight basis to provide an independent ion for tracing. Additional subtreatments included planting potatoes without hilling in a furrow, additional application of N late in the season, and cropping a high N fertility area.The overall average fresh weight tuber yield was 515 q/ha. Total yields were the same in both CON and IMP treatments for both years. However, grade A tuber yields were greater on the IMP treatment than the CON treatment in 1973 when irrigation was applied every 3 rather than every 5 days, and fertilizer N was applied in 11 rather than three doses. The greater grade A tuber yields occurred despite a decrease in fertilizer N from 260 to 170 kg N/ha and a decrease in irrigation water applied from 45 to 27 cm. Evapotranspiration and N uptake by tubers were not appreciably affected by irrigation and N management.In 1973 most of the N applied at planting was leached except where S‐coated urea was used to provide a source of slow‐release fertilizer N. Application of fertilizer N and Cl with the irrigation water resulted in substantial variability in inputs over the plot area due to variation in the water distribution. The average coefficient of variation for inputs of fertilizer and water was 19% and the average uniformity coefficient (Cu) was 85%.A satisfactory mass balance of water, N and Cl for potatoes grown in the dosimeters was obtained. Drainage accounted for considerable amounts of the water, N, and Cl outputs with nearly all of the remainder going to and plant uptake. The carefully managed IMP treatment decreased NO3‐N leaching from 200 to 120 kg N/ha and lowered the overall average NO3‐N concentration of the leach ate from 23 to 16 mg N03‐N/liter. However, the additional costs required to effect a small savings in N fertilizer is probably not justified.