Long term trend analysis of changes in tomato (Lycopersicon esculentum) water use efficiency in the southern, southwest and central regions of Iran

In order to improve water utilization management the trends of changes in crop water requirement (CWR), yield, cultivation area and water use efficiency (WUE) of tomato in some regions of Iran evaluated in a 23-year long term (1990-2013) by measuring evapotranspiration (ET) and crop coefficient (Kc). Highest (1137 mm) and lowest (642 mm) CWR of tomato observed in Yazd and Shahrekord cities respectively. Unlike Dezful and Shiraz, this characteristic has a significant increasing trend with a slope of 5.6 mm per year in Fasa. Furthermore, unlike Fasa, tomato yield in Ahvaz, Bandar Abbas, Shahrekord and Yazd has a significant increasing trend. The maximum (49.5 ton/ha) and minimum (19.4 ton/ha) tomato yield and also the maximum (5.6 Kg/m3) and minimum (2.4 Kg/m3) WUE was observed in Fasa and Kerman, respectively. However, the highest reduction (0.1 kg/m3) and highest increase (0.07 kg/m3) in WUE per year was obtained in Ahvaz and Fasa respectively. The results of this study showed that the WUE has a linear relationship with tomato yield. So that the water consumption per 100 kilograms of tomatoes yields per unit of area increased 0.1 kg/m3. While there was no logical relationship between WUE and CWR. By drawing the boundary-line, which represents potential yield against the CWR, high fluctuation of tomato yield in a steady interval of water requirement was estimated. Overall, the lack of a relationship between the WUE and CWR in the range of 600 to 1000 mm was due to yield gap caused by malpractice in the farms.