Evaluation of Physical and Economic Productivity of Irrigation Water in Canola Cultivation (Case study of Behbahan)

Background and Objectives
A large part of Iran is located in arid and semi-arid climates. Despite the existing shortcomings, Iranian agriculture is highly dependent on irrigation water. As water is considered as the most important and limiting input of agricultural production in Iran (Zibaie, 2007). Rapeseed (Brassica napus L.) is the third annual oil crop in the world after palm oil and soybeans, which is cultivated for its edible oil and is easily replaced by cereals (FAO, 2013). The main goal in improving agricultural water productivity in the world is to increase agricultural products with less water consumption, thus reducing the share of water in the agricultural sector and allocating more water to other uses and, most importantly, the water needs of the environment (Heydari, 2014). So far, no report has been presented on the evaluation of different irrigation systems in rapeseed cultivation in East Khuzestan. The main purpose of this article was to measure the irrigation water of rapeseed fields in Behbahan city and compare their physical and economic water productivity. In this way, the physical and economic productivity of water under different agricultural management and in irrigation systems can be compared and evaluated.
Methodology
This project was implemented in the field to determine canola irrigation water under the management of farmers in Behbahan city. In 26 farms, the volume of canola irrigation water (without interfering with their irrigation program) was measured. To determine the volume of irrigation water, first the amount of inflow from the selected water source was measured with a suitable device (WSC flume, meter or ultrasonic flow meter). Linear multivariate regression analysis was used to investigate the effects of the independent variable on the above dependent parameters. Water requirement was calculated based on the FAO Penman-Monteith model using the daily statistics of Behbahan Synoptic Meteorological Station (minimum and maximum daily temperature, minimum and maximum daily humidity, wind speed and maximum sunny hours) and using ETCalculator software. One-way analysis of variance was used to show a statistically significant difference between the means of two or more independent groups. To compare physical and economic productivity indicators of irrigation water, there was a need to resolve the difference. Therefore, the standard Z-Score standardization method was used to resolve the scale difference. SPSS16 software was used for statistical analysis.
Findings
The average irrigation water productivity in 26 farms ranged from 0.351 to 1.545 kg per cubic meter and economic water productivity ranged from 6940 to 3719660 Rials per cubic meter. Irrigation water volume with t-statistic (-11.193) and equivalent beta coefficient (-0.056) had a significant negative effect at the level of 1% on the irrigation water productivity and a significant negative effect at level 5% had on the economic water productivity. The method of irrigation of selected farms (surface or sprinkler) had a significant effect at the level of 5% on the physical and economic irrigation water productivity. The calculated scores according to Z-Score showed that 31% of the farms that had sprinkler irrigation system were in good condition in terms of physical and economic productivity of irrigation water and none of the farms in the surface irrigation system were ranked well in terms of irrigation water productivity, but 8% of the irrigation farms had good economic productivity. The results of Pearson correlation coefficient showed that rapeseed yield had a positive and significant correlation at the level of 1% and 0.608 with irrigation water productivity, while yield had no significant correlation with economic water productivity.
Conclusion
Comparison of the results of average traits showed that the implementation of sprinkler irrigation system in the studied farms has increased the physical and economic productivity of irrigation water. The high cost of implementing the irrigation system in agricultural lands has not caused these farms to have lower physical and economic productivity than surface irrigation farms, but instead the cost of implementing the irrigation system during ten years of using this system has led to better management use of irrigation water, increase the physical and economic productivity of irrigation water. This management is mainly implemented by irrigation and drainage companies by shortening the irrigation period and increasing irrigation times. Prevents grain filling and by adjusting the irrigation hour at each irrigation time by moving the sprinklers by irrigation workers, prevents water wastage and deep percolation of water from the root zone and compared to surface irrigation from water losses prevents the end of irrigation furrows. This management, along with reducing labor costs while keeping the canola crop, has reduced costs and increased the physical and economic productivity of irrigation water.