Yield-evapotranspiration relationships and seasonal crop coefficients for frequently irrigated potatoes

‘Russet Burbank’ potatoes (Solarium tuberosum L.) were subjected to various levels of water application during the growing season. Water applied, rainfall, and soil water changes were measured at weekly intervals. Tuber yield and quality increased as water consumption increased from 300 mm to 650 mm. Evapotranspiration (ET) increased rapidly from plant emergence until early tuber bulking and declined gradually as plants matured. Comparing ET with pan evaporation provided coefficients (K) which changed in response to crop growth stages. K increased from 0.3 at emergence to over 0.8 during maximum leaf area and declined with crop maturity. The relationship between K and crop growth stage can be used with confidence in scheduling irrigation of potatoes in north central Oregon.