Potential effects of different irrigation and drainage regimes on yield and water productivity of two potato varieties under Estonian temperate climate

To examine the potential effect of water management on potato yields, the crop model POMOD (POtato MODel) was used. The effects of irrigation, drainage and two-way water management (irrigation + drainage) were simulated with and without natural outflow (percolation to deeper soil layers and runoff). Calculations were performed for two Estonian mainland locations (subcontinental Tallinn for the period 1920-2011, continental Tartu, 1901-2011) and one insular, maritime region (Kuressaare, 1923-2011) as well as for an early and a late potato variety, 'Mara' and 'Anti', accordingly. In the reference series without water management, the average yields were 18% higher for the late variety compared to the early variety. The mean reference yield in Kuressaare was 8% lower than in mainland locations. The mean water productivity (WP) calculated per evapotranspiration was nearly 45 kg mm(-1) ha(-1) (dry mass), somewhat higher for the late variety compared to the early variety. The highest and most statistically significant (P < 0.05) increase of yield was achieved from the two-way water management. In the case of natural outflow (water losses to deep percolation and runoff exist), the effect of irrigation prevailed over drainage in all locations. Without outflow, the effects of irrigation and drainage were comparable in the mainland, but the effect of drainage remained negative in Kuressaare. Generally, a positive effect on tuber yield occurred more often from irrigation than from drainage. However, in the case of restricted outflow in the mainland locations, the maximum yield gain from drainage exceeded the yield increase from irrigation by approximately two-fold. The extra yield depended on the amounts of irrigation or drainage by a second order polynomial, while the productivity of irrigated or drained water was, on average, markedly lower than the WP calculated per evapotranspiration, which had a linear relation. Irrigation and drainage water amounts under 50 mm did not have any positive effect on yield. The need for irrigation is highest in maritime climate covering Estonian islands and Western and Northwestern coast. In these regions, irrigation increases the mean yield by 18-26% and decreases its variability two-fold. In continental locations, if natural outflow is restricted, implementation of two-way water management projects should be considered, as its effects on yield quantity as well as on stability exceed the sum of separate effects from irrigation and drainage. (C) 2015 Elsevier B.V. All rights reserved.