بررسی اثرات روش آبیاری و شبکه آبیاری بر بهره‌وری فیزیکی و اقتصادی آب در ذرت علوفه‌ای (مطالعه موردی بهبهان)

Background and Objectives
Considering the lack of renewable water resources in the world and the high share of the agricultural sector in water consumption, makes increasing water productivity very important. Corn is an important type of fodder that is harvested for consumption as silage of the whole plant (Coors et al., 1997). Despite having one harvest stage, this plant has a high dry matter yield. Its silage is easily prepared and it is a tasty fodder with stable quality for livestock and has higher energy than other fodder (Curran and Posch, 2000). Research results in Hamedan province in two traditional and modern irrigation systems showed that the average physical water productivity for fodder corn in traditional and modern irrigation systems was 5.11 and 6.67 kg per cubic meter of water, respectively. The average economic water productivity for fodder corn in traditional and modern irrigation system was 7678 and 10068 rials per cubic meter of water, respectively (Seyedan and Mottaghi, 2019). The main purpose of this article was to measure the water received in the field of fodder corn fields in Behbahan city and to investigate their physical and economic water productivity. To do this, the applied irrigation water, physical and economic water productivity under different agricultural management and in irrigation networks and systems can be compared and evaluated.
Methodology
This research was carried out in the field and in order to investigate the effects of independent variables on applied irrigation water, physical and economic water productivity in the cultivation of fodder corn in irrigation methods and networks under the management of farmers in the cropping season (2016-2017). It was implemented in Behbahan city. Thus, in 12 farms of the farmers, the applied fodder corn irrigation water was measured (without interfering in their irrigation program). The effective rainfall of the 2016-2017 crop year in Behbahan city was calculated using the United States Department of Agriculture (USDA) method. To determine the applied irrigation water, first, the inflow rate from the selected water source was measured with a suitable device (WSC flume, water meter and ultrasonic flow meter). The SPSS16 software was used for step-by-step linear multivariate regression analysis. Linear multivariate regression analysis was used to investigate the effects of independent variables on dependent parameters. One-way analysis of variance was performed with SPSS16 software. The purpose of using one-way analysis of variance was to statistically show a significant difference between the average of two or more "independent" groups. In order to compare the indicators of physical and economic water productivity , there was a need to resolve the difference. Therefore, to solve the scale difference, the common method of Z-Score standardization was used.

Findings
The results of the analysis of variance in the regression model showed that the growth period of the plant had the most significant positive effect on the amount of irrigation water with the t-statistic of 5.288. Performance with a t-statistic of 5.919 had the most significant positive effect on economic water productivity. Among the independent variables, yield and applied irrigation water had the most significant positive and negative effect on the physical productivity of water with the values of 6.419 and -6.381, respectively. The applied irrigation water varied from 4826 to 14733 cubic meters per hectare. The results of the analysis of variance and the descriptive results of the mean of the traits showed that the highest value of physical water productivity was equal to 10.128 kg/m3 in rain irrigation and the lowest value was 4.818 kg/m3 in surface irrigation in the traditional network. They had a significant difference. The calculated Z-Score values showed that 50 and 33% of the sprinkler and surface irrigation farms (modern network) had acceptable economic productivity, but 100% of the surface irrigation farms in the traditional network did not provide acceptable economic productivity.
Conclusion
The amount of irrigation water used in the fields with sprinkler irrigation method was 46 and 33% less than traditional and modern network fields that were irrigated by surface irrigation method. Also, the consumption of irrigation water in the surface irrigation method in the traditional network was 20% more than the surface irrigation in the modern irrigation network. This increase in water consumption was effective in reducing the irrigation efficiency of traditional networks compared to modern networks that irrigated with surface irrigation. The reason for the higher consumption of irrigation water in the surface irrigation method in the modern network compared to sprinkler irrigation can be attributed to the following factors: 1- The lack of irrigation management during the change of the irrigation shift of the fields, which sometimes happens due to the absence of the irrigation worker during the shift change. 2- lack of control of the incoming water of the fields due to the lack of meters or devices to measure the incoming flow. 3- Improper leveling of lands under the modern irrigation network, which increases the irrigation time of these fields. By covering the traditional irrigation canals with concrete or other coverings suitable for the climate of the region, water losses can be reduced. Also, the necessary training for the correct use and management of irrigation water according to the different stages of fodder corn growth will be effective in reducing water consumption. Water according to the stages of growth and development of the plant prevented the occurrence of under-irrigation stress in the stages of flowering and seed filling, which is the most important stage sensitive to water stress.