Water limitations on potato yield in Estonia assessed by crop modelling

For the reference run the yields were higher for the late variety and lowest in dry Kuressaare. The average irrigation requirement was 30-45 mm for the early and 47-58 mm for the late variety in continental locations, but over two times higher in insular Kuressaare. In continental stations the need for drainage was 30-40 mm per growing period in addition to natural outflow (about 20-25 mm more without outflow). In Kuressaare the mean amount of excess precipitation was only 9-20 mm and its removal had a mostly negative effect on yield due to increasing water deficit during the following dry period. In over half of the years the crops suffered from both water shortage and excess. The greatest increase in yield was achieved when both drainage and irrigation were applied. The benefit from irrigation alone was also considerable, more for the late variety and in Kuressaare. The effect of drainage was most evident in conditions of restricted outflow The negative effects of drainage on yield, as observed in years when drainage led to increasing water deficit in subsequent periods, lowered the average impact of drainage. However, in some cases the highest yield losses were observed in years with excess water.