Water use of irrigated potato (Solanum tuberosum L.) grown under free air carbon dioxide enrichment in central Italy

Increased atmospheric CO2 concentration are known to affect crop performance and water consumption. This study evaluated potato yield and water use efficiency (WUE) by assessing tuber yield and monitoring actual crop evapotranspiration (ET) for two consecutive years. Potato (Solanum tuberosum L.) cv. Bintje was grown in a free air CO2 experiment (FACE) in central Italy, under both ambient and elevated CO2 (550 (mu)mol mol^-1). FACE, ringed and non-ringed control plots were arranged in a replicated Latin-square experimental design. The best cultural practices were applied including ample water supply. ET was monitored throughout the crop cycle, on an hourly basis, by using the residual energy balance approach. Net radiation and soil heat flux were measured on three replicates for each treatment. Canopy radiative temperature was also monitored on the same plots by means of infrared thermometers, while wind and temperature profiles were measured separately at a central location. Instruments were frequently exchanged to avoid systematic errors due to sensors mismatch. Sensible heat flux was computed on the basis of air and canopy temperatures and of the aerodynamic resistance--and latent heat flux as the residual of the crop energy balance. Mean seasonal daytime canopy temperature of FACE was increased 0.6 (degree)C in 1998 and 0.9 (degree)C and 1999 as a result of increased canopy resistance. As a result, mean daily water use in 1998 was 6.58+-0.12 and 7.22+-0.14 mm per day for FACE and control, respectively. On a seasonal basis, FACE used 342 mm of water compared with 375 mm used by the crop under ambient conditions. During the second year of the study, the effect of fumigation on the water use by the crop was more evident. Daily mean water use in FACE was 4.98+-0.24, compared with 5.9+-0.25 under ambient conditions while total seasonal water consumption was 297 and 353 mm, respectively. The overall FACE water saving across both years was 11.8%. The higher tuber yield and lower ET lead to a substantial increase in WUE of FACE, namely 70 and 67% in 1998 and 1999, respectively. These figures are higher than reported in previous FACE experiments, for either cool or warm seasons crops and suggest that this basic commodity would benefit from a CO2 enriched air, both in terms of yield performance and water savings.