Potential Effect of Water Regulation on Potato Yield

To examine the effect of water regulation on yields, alternative water balance schemes were added to a potato production model POMOD [1]. Effects of irrigation, drainage and two together were investigated with and without natural outflow [2]. Calculations included two Estonian mainland locations (Tallinn, Tartu) and island region (Kuressaare), an early and a late variety.In case of natural outflow mean meteorologically possible yields (MPY) were 9% higher in mainland compared to island for both varieties, absence of outflow levels these differences (Table 1). Yield of the late variety was 18% higher than the yield of early variety, with higher difference between varieties in Tartu (23-24%). In case of natural outflow the losses of yield were caused mainly by water deficit, without outflow the effects of irrigation and drainage equalized in mainland. Drainage had always negative impact in Kuressaare. Two-way amelioration had the strongest, always statistically significant impact. Effect of irrigation was higher for the late and drainage mostly more positive for the early variety. When outflow was restricted, the maximum gain from drainage exceeded gain from irrigation approximately twice in mainland. Extra yield depended on the amount of irrigated/drained water by the second order polynomial, with higher correlations for irrigation. Irrigation or drainage water amounts under 50mm did not have positive effect on yield.The mean WUE, calculated per evapotranspiration, was near 200kg mm-1ha-1, some higher for the late variety. WUE increased by dry conditions and drainage, decreased by irrigation and absence of outflow. Mean efficienciesof irrigated and drained water, being well in linear dependence on added and removed water amounts, were markedly lower than WUE calculated per evapotranspiration. Efficiency of water use in two-way amelioration is proposed as tool to assess rationality of energy use on polder-type two-way amelioration systems.