عنوان مقاله [English]
نویسندگان [English]چکیده [English]
Water shortage and drought are two phenomena that are unavoidable due to the high variations in soil moisture in time and place during the entire growing season. Generally, the irrigation water depth varies under different conditions of land shortage, drought and salinity stress, or a combination of these conditions. When irrigation with this depth can be maximized, net income can be maximized. In order to determine the optimum depth, various tools such as the production function of the yield, irrigation water and its derivatives, initial and current costs, yield prices and information on the water and land are needed. The turnip (Brassica rapa L.), as a strong source of nutritional supplementation, contains a variety of antioxidants such as vitamins and schucosinolates (Norin et al., 2010). Turnips are used in fresh and dried forms for human feed.
Since there has been no research in the field of determining the optimal production function of water-salinity-turnip yield in the country, the aim of this study is to find the optimal function of turnip production in combination with salinity and drought so that the water consumption can be minimized by using saline water.
This experiment was conducted as a factorial based on completely randomized design with three replications including two factors of salinity and irrigation water. Four levels of irrigation water salinity including two factors of salinity and irrigation water were applied, with three replications. The four levels of saline irrigation water include: S1: 0.7 (as a control), S2: 4, S3: 8 and S4: 12 ds/m and three irrigation water levels were considered as W1: 100% of crop water requirement, W2: 75% of W1, and W3: 50%W1.
The statistical data of the performance of the project implementation were fitted with the SPSS software and various forms of production functions were determined. For this purpose, the optimal production function, a statistical sensitivity analysis, was performed and then the relevant statistics determined the role of each entity in generating functions quantitatively. To evaluate the validity of the obtained functions, the analysis of the remaining errors and the differences between the measurement and prediction values were used. The statistics required for this study were the maximum error (ME), root means square error (RMSE), the coefficient of determination (R2), modelling efficiency (EF), and residual coefficient of variation (CRM).
The results showed that the highest yield was obtained in control treatment (W1S1) and 75% W1 (W2S1) treatments at the rate of 6.66 and 7.42 kg/m3, respectively. In addition, by increasing the drought and salinity stress, the water use efficiency decreased. The Ky values at the same conditions of salinity and drought stress were more than Ky in drought stress and less than Ky in salinity stress conditions. Therefore, it can be concluded that the effect of salinity stress on reducing yield is more than drought stress. Subsequently, Ks values showed that by increasing salinity and drought stress, the crop evapotranspiration was decreased. In order to adapt to the water shortage, it can use the optimal production function for the turnip yield in Kashmar.
It can be stated that in drought stress conditions, evaporation and transpiration reduction is due to the water deficiency, and in salt stress conditions is due to the decreased water absorption because of decreasing osmotic potential of root zone. The results of the product curves showed that by increasing the amount of irrigation water, the water with higher salinity can be used.