Effect of Irrigation Management on Water Use Efficiency in Tomato Farms

Over-harvesting of water resources along with climate change led to the aggravation of the water shortage crisis. Therefore, correct management and planning for sustainable use of water resources are of high importance. In this situation, one of the most effective solutions is to increase agricultural water productivity. The main goal in improving agricultural water productivity is to save water consumption along with increasing the yield of agricultural products. There is 128,000 hectares of tomato cultivated land, standing for 1.1% of the total cultivated area in Iran. Irrigation management is one of the most effective and recommended ways to control water consumption in tomato farms. Nevertheless, it is necessary to study the mentioned solution on large-scale such as province with considering different climate, farm area, irrigation system and irrigation management in the field. In this research, irrigation management was the proposed solution to improve the water productivity. Initially, the current status of irrigation management in 12 tomato farms was investigated. Then, the effect of the irrigation management, specifically the corrected irrigation schedule, were evaluated owing to enhance the water productivity.

12 tomato farms were firstly selected in the agricultural lands of Zanjan province. Most of the experimental farms were equipped with drip tape irrigation systems. In the second phase, two farms were selected and the proposed irrigation schedule were implemented in order to improving the water productivity. Each farm was divided into two parts; one with real conditions (farmers' management) and another with controlled conditions. In the controlled treatments, irrigation management was implemented through optimization of irrigation time. In each farm, basic information such as area, physical and chemical properties of soil and water quality were determined. Irrigation information (such as inflow discharge and irrigation schedule) was measured and determined at least three times during the cropping season. Soil moisture were measured before and after irrigation in order to calculate the water application efficiency. The amount of harvested product and production costs were obtained at the end of the cropping season through measurements and interviews with farmers. In this research, the indicators including the volume of consumed water, the water use efficiency, and the physical and economic efficiency of water have been calculated to analyze the water productivity.

The minimum and maximum of consumed water in tomato farms was measured as 6142 and 17580 m3/ha, respectively (with an average of 10669 m3/ha). The average of consumed water in farms with surface irrigation systems equals to 16600 and in farms equipped with drip tape irrigation systems is about 9483 m3/ha. While the actual water requirement in the studied area is between 6120 and 6950 m3/ha. The amount of application efficiency was calculated in the range of 34.8 to 90% (66% on average). The average of this index in surface and drip tape irrigation systems were determined 39.9 and 71.4%, correspondingly. The minimum and maximum values of tomato yield were measured 40 and 140 ton/ha (with average of 77.2 ton/ha). The results of the second phase of the research showed that the application of proper irrigation management leads to a significant reduction in water consumption. Implementation of this strategy in farms 201 and 202 led to a 39% decrease and a 8% increase, respectively of water consumption during the cropping season. Irrigation schedule in some farms is relatively fixed and they have less flexibility compared to changes in net water requirement. The water use efficiency (CPD) was calculated as an important criterion in order to investigate physical productivity. The value of CPD was obtained in the range of 2.3 to 22.8 (on average 8.7). As the consumed water increases to a certain amount (approximately 10000 m3/ha), the value of the CPD shows an upward trend, However, with the increase from the mentioned value, the value of the CPD drops. Implementation of modified irrigation management has led to a significant increase in CPD index. On average, the value of the CPD in the controlled plots has increased by 29.5% compared to the real conditions.

In some farms, the irrigation schedule was not in accordance with the net irrigation requirement and excessive irrigation was done by farmers. It was especially evident in the first half of the crop growth period, and with the reduction of groundwater level, the depth of irrigation water became closer to the actual requirement. In fact, the limitation of water resources was recognized as the main factor controlling water consumption in most farms. However, it is possible to considerably reduce the consumed water and improve the productivity by applying proper irrigation management (specifically correcting the irrigation time). Using the results of the present research through the preparation of understandable instructions for farmers can lead to the prevention of excessive irrigation and the control of water consumption in farms.