Yield, water use efficiency and nitrogen recovery in potato: Influence of water table depth

A lysimeter experiment was performed to study the influence of three permanent water table depths (0.45 m, 0.85 m and 1.20 m below the soil surface, WT45, WT85 and WT120) and a variable one (ranging between 0.40 m to 1.30 m, WT(var)) on photosynthesis, yield, tuber quality, WUE and NUE. Treatments were compared with a well-watered top-irrigated control. The control was drip irrigated restoring the entire ET every time 40 mm of soil water had been depleted, while in the other treatments water was supplied by underground irrigation. In the WT(var) the soil was saturated at the beginning of the experiment (the water table was at 0.40 m) and then the lysimeter was no longer irrigated. The control showed the highest CO2 assimilation, during both flowering and tuber maturation, and thus the highest shoot DM production and tuber yield. Plants under WT45 conditions were stressed, since soil moisture exceeded field capacity even in the top layer (0.15 m), and suffered reductions in photosynthesis, total biomass and yield. These soil moisture conditions proved to be detrimental especially during the first period of tuber formation. DM yield in WT85 and WT(var) did not significantly differ from that in WT45, although water consumption was reduced. The lowest water table depth (1.20 m) was the most damaging for DM production. Tuber FW reductions of 15%, 19%, 46% and 33%, compared with the control, were observed for WT45, WT85, WT120 and WT(var), respectively. The tuber yield reductions were either due to number of tubers for WT45 and WT(var), or tuber weight for WT85, or to both for WT120. Tuber size grading was not affected by the treatments and minor changes in the qualitative traits were detected. A good recovery and efficiency of the N supplied by fertilization both in the control and in WT45 were observed.