Water – Fertilizy production Function and Water use eficcenty two of cotton in the Golestan

Population growth affects the need of communities for crops. No country is excluded from this rule. Cotton is one of the strategic products in Iran. Increasing the cultivating of this crop reduces the country's need for importing. On the other hand, water scarcity has caused human societies to seek solutions to eliminate the consequences of this issue. One of these methods is to find the exact relationship between the amount of water and fertilizers consuming and product yield. In other words, the amount of yield achieved per unit of consumed water and fertilizer is considered. Knowledge about these relationships can help improve water and fertilizers management. Iran is one of the countries that despite the increase in population growth water resources are reducing day by day. Therefore, it is necessary to determine the exact relationship between water and fertilizer units and cotton yield. This test was a step towards optimizing and improving management. Therefore, the results of this experiment can be used to answer questions related to water-fertilizer relations and yield. In order to evaluate the cotton yield response to the combined effect of water consumption and fertilizer use, an experiment was conducted in 2012 at Hashem Abad Station in Gorgan, Iran. The experiment was carried out with six water levels of 0% (in the case of dry or without irrigation), 36%, 66%, 88%, 100%, 132% of water requirements, and four fertilizer levels of 0%, 33%, 66% and 100% of fertilizer requirement, and Two cotton cultivars of Golestan and B 557 were carried out in the form of strip split plot with three replications. Treatments of fertilizer and cultivars were selected in strip and perpendicular to irrigation strips and these strips were randomly placed in each replicate. From the collision of these strips perpendicularly, plots with dimensions of 2.5 × 3 m were created. Cotton cultivation was carried out on May 25, 2012, at a distance of 25 centimeters and a row spacing of 75 centimeters. There were 4 planting lines in each plot. Among these, two marginal and two midline lines were considered for yield measurement. In this experiment, the soil was tested before planting and the texture, salinity, alkalinity, and fertility needs of the farm were determined. Sprinkler irrigation method was applied by linear system. Spray sprinkler radius was 12.5 meters and the sprinkler spacing was 6 meters. Before irrigation, the moisture content of the soil was tested by weight. Irrigation time was determined based on soil moisture content, sampling the second strip (5W). The duration of irrigation was calculated based on the required depth to field capacity and the intensity of spraying in the second strip (5W). During the cropping period, the moisture content in the base treatment was in terms of crop capacity, except for the two cases provided by irrigation. Irrigation was carried out in the quiet hours of the night due to the calmness of weather conditions and the reduction of winding and evaporation losses. Before sunrise, the amount of irrigation water was measured by canisters in the middle of each plot. Fertilizer was provided manually in two stages: 40% fertilizer requirement of each plot before planting, and 60% after planting and before flowering. Plant yield was obtained from the first and second harvest. Functional weight included fiber and cotton seed. In order to determine the best production function, simple linear function, logarithmic and quadratic regression were used and the results were evaluated and assessed. The evaluation of the results of fitting the logarithmic yield function of Golestan cultivar showed that the statistical characteristics of RMSE, R2, EF and ME respectively were equal to 0.12, 0.86, 0.007 and 0.33. Comparison of statistical characteristics of linear and quadratic functions with logarithmic function revealed that the logarithmic function for different values of water-fertilizer simulates the yield of Golestan cultivar more precisely. On the other hand, the quadratic equation was selected as the weakest production function in Golestan cultivar, with values of RMSE, R2, EF and ME equal to 0.55, 0.73, 0.09 and 0.61, respectively. These results for the B-557, despite the change in the different values of the indices, had similar results with Golestan cultivar. Water use efficiency for Golestan cultivar and B 557 was obtained in W3 treatment (36% water requirement) and W1 (0% water requirement, dry farming and cultivation without irrigation), which indicated Golestan cultivar had higher water use efficiency than B-557