Excess and deficient water stress effects on 30 years of Aroostook County potato yields

Potato production can be adversely affected by both deficient and excess water. A plant water excess (PWE) index is defined as the difference between actual evapotranspiration (AET), which is equal to the difference between rainfall and runoff, and potential evapotranspiration (PET), as computed by the Thornthwaite method, for those 5-day periods when AET exceeds PET. A growing season PWE index was equal to the accumulation of 5-day average PWE values and was calculated for each of 30 years of data. Similarly a plant water deficit (PWD) index was defined as the PET-AET for those 5-day periods when PET exceeds AET. Potato yields during the 30-year period were related to the combined effect of yearly water excess (PWE) and deficit (PWD) and can be described by the multiple regression relationship of Y = 43.558-0.74527 (PWD + PWE)+ 0.031883 (PWD × PWE). This model has a multiple r² value that indicates 46% of the yield variation can be accounted for by the combined yearly influence of deficient and excess water. The results suggest that maximizing potato production in the humid Northeast requires a water management system that includes both supplemental irrigation and drainage.