Plant water deficit effects on Aroostook County potato yields over 30 years 1

We estimated potential irrigation requirements for potato production in Aroostook County, Maine. These requirements were computed from a Plant Water Deficit (PWD) index based on readily available streamflow and climatic parameters. Actual evapotranspiration (AET) figures for specified time periods were assumed to equal the differences between rainfall and runoff. Runoff was computed from differences between streamflow and baseflow for the Aroostook River. Potential evapotranspiration (PET) was computed by the Thomthwaite method. The PWD was established as the difference between PET and AET. The yearly PWD index was then equal to the accumulation of 5-day average values for the PET-AET for each of 30 years of data. Similar computations were made for 10-and 20-day intervals. A yearly temperature index based on Growing Degree Day (GDD) units was also computed. Potato yields were then compared to PWD and GDD values. Results show PWD figures ranging from 11.74 cm to 25.78 cm. There was a highly significant negative correlation existing between PWD and potato yield.