Water and Nitrogen Applications for Potato: Commercial and Experimental Rates Compared to a Simulation Model

Abstract

ABSTRACT Irrigated potato is a major commercial crop in the semi-arid regions of Washington, Oregon, and Idaho. With gross returns of $3000 to $6000 per acre, cost to growers for applying excess water and nitrogen is small compared to the potential income loss. Potatoes are frequently grown in this region on extremely sandy soils with very low soil organic matter. Recent studies have found nitrate contamination of ground water in this region. Because of the high levels of water and agricultural chemicals applied, the irrigated potato crop is a major potential source for nitrogen and other chemicals in the ground water. If water and other materials can be applied just as they are needed, nothing will be moved below the crop rooting zone during the growing season. The SIMPOTATO growth model simulates daily water and nitrogen requirements for the potato crop based on initial soil status and daily weather conditions. Simulated water and nitrogen requirements are compared to actual applications on commercial fields in 1988 and 1989 and on 1992–95 experiment fields, with minimal water and nitrogen inputs. The simulated water and nitrogen requirements were close to the actual amounts applied to the experiment fields but were considerably less than applied to the commercial fields. Simulated nitrogen leaching on the experiment fields was near zero, while simulations showed considerable leaching on the commercial fields. No measurements of actual leaching were available. Suggestions are offered on how to apply this technology in commercial farming.