Effects of potato cropping practices on nitrate leaching in the Columbia Basin

This study examined the contribution of irrigation and nitrogen (N) fertilization to leaching of nitrates below the potato rooting zone. Virgin desert and an intensively cultivated site were cropped to Russet Burbank potato under a range of irrigation frequencies (IF = 1, 2, or 3 days), irrigation rates (IR = 0.7, 1.0, or 1.3 {dollar}times{dollar} recommended), and N fertilization rates (NR = 220, 390, or 560 kg{dollar}cdot{dollar} ha{dollar}sp{lcub}-1{rcub}).{dollar}; Soil and soil solution to 1.2 m, and petiole samples taken throughout the season were analyzed for NO{dollar}sb3{dollar}-N, NH{dollar}sb4{dollar}-N, pH, electrical conductivity (EC), organic matter, and/or moisture content as appropriate. Porous cup lysimeters (PCL) at 0.6 and 1.2 m were used to extract soil solution. Aerial biomass and tuber yield and quality were determined.; EC, NO{dollar}sb3{dollar}-N, and NH{dollar}sb4{dollar}-N levels increased linearly with increasing NR at both sites. Soil pH did not change at the desert site but decreased linearly with increasing NR at the cultivated site. Organic matter (OM) was not affected by NR at either site. The response of soil to NR was generally limited to the 0-0.3 m depth. Soil water content decreased linearly with increasing NR at the uncultivated site, but not at the cultivated site.; IR and IF did not affect soil pH, EC, or NO{dollar}sb3{dollar}-N levels. However, NH{dollar}sb4{dollar}-N decreased linearly with increasing IR in the top 0.3 m, and OM increased with IR at 0.6-0.9 m but decreased below 0.9 m.; Soil NO{dollar}sb3{dollar}-N levels increased to 1.2 m on the uncultivated site in response to 390 kg{dollar}cdot{dollar}ha{dollar}sp{lcub}-1{rcub}{dollar} NR and to 0.9 m for 560 kg{dollar}cdot{dollar}ha{dollar}sp{lcub}-1{rcub},{dollar} but did not respond to 220 kg{dollar}cdot{dollar}ha{dollar}sp{lcub}-1{rcub}{dollar} NR. At the cultivated site, soil NO{dollar}sb3{dollar}-N increased to 0.9 m in response to 560 kg{dollar}cdot{dollar}ha{dollar}sp{lcub}-1{rcub}{dollar} NR, but only to 0.3 m for lower NR.; PCL's reliably extracted sufficient soil solution, but were not consistently reliable for monitoring soil NO{dollar}sb3{dollar}-N.; Petiole NO{dollar}sb3{dollar}-N concentrations increased with increasing NR, and decreased with increasing IR, but were not affected by IF. Tuber yields increased with increasing IR, but were not affected by either NR or IF. Tuber numbers decreased with increasing NR and IR. Tuber solids and hollow heart were not affected by the treatments. Fry color darkened linearly with increasing irrigation rate.; Results of this study tend to refute claims that responsible potato producers in the Lower Umatilla Basin are contributing insignificantly to increased groundwater NO{dollar}sb3{dollar}-N levels.