DIFFERENCES IN NITRATE LEACHING UNDER VARIABLE AND CONVENTIONAL NITROGEN FERTILIZER MANAGEMENT IN IRRIGATED POTATO SYSTEMS

摘要

Over the past ten years there has been increased attention to nitrate contamination of groundwater, particularly to leaching associated with agricultural activities. In the Pacific Northwest, nitrate in the groundwater is a concern in potato (Solanumtuberosum L.) cropping systems. In this region potato is generally grown under center pivot irrigation in coarse textured soils. The combination of high fertilizer nitrogen (N) requirements of potato and coarse soil texture lead to increased risk of nitrate leaching. Site Specific Crop Management (SSCM) and Variable Rate Application Technology (VRT) are potential tools to develop strategies for environmentally sound nitrogen fertilizer management in these systems. In this study, two adjacent fields wereselected in row crop rotations (potato as the 1999 crop). Each field was soil sampled on a 61m x 61m grid to establish background soil N levels. One field was fertilized with variable N rates while the other was fertilized with a single N rate based onthe field average. To evaluate field N dynamics monitoring sites were established based on landscape position (knoll, slope, valley) and soil test organic matter content (high, low). Nitrogen flux was monitored with ion-exchange resin probes at two depths, one in the root zone and one below the root zone. Soil moisture and soil and petiole nitrate were monitored throughout the growing season. This paper will discuss the leaching differences found under the two fertilizer management strategies.