Assessment of yield and yield components production function of safflower under deficit irrigation and different salinity levels
Attention to water consumption management in agriculture section as the main consumer of water in Iran is vital. Increasing population growth and consequently increasing water consumption in various sections such as industry and drinking water make necessary to use irrigation water more efficiently. One of the important and debatable issues in agricultural section is water resources shortage for usage in irrigated lands. In addition to water resources shortage, soil and irrigation water salinity are the other serious restrictions for crop production in arid and semi-arid regions all over the world, too. Determination of crop production function is opening the path for the programming and policy of agricultural productions. Estimating crop production functions were generally done with two procedures. In the first way, relationship between yield-water; yield-salinity or yield-water-salinity are expressed based on the theoretical and empirical models, quantitatively. In the second way, crop production functions were estimated by the effect of different amounts of quality and quantity of irrigation water on crop yields using field observations and statistical analysis. Safflower as a moderately tolerant plant species to salinity is planting in arid and semi-arid regions where salinity is a serious restriction for crop growth. According to the conducted researches, drought stress in flowering period of safflower prohibits from pollination and resulting seed formation is reduced and ultimately grain yield affected. Assessing of safflower sensitivity to simultaneous effects of drought and salinity stress on yield-water-salinity production function has not been yet studied in arid Kashmar region. Therefore, in this study it was tried to survey the optimum crop production function of safflower by applying drought stress and irrigation with saline water under pot planting conditions.
This greenhouse study was conducted in winter 1400 and spring 1401 in Kashmar region. In order to better control of conditions governing the experiment, in terms of applying salinity and irrigation treatments and prevent from frost bitten of plant, pot research was used in greenhouse ambient. The experiment was done as a factorial in a form of completely randomized block design with three replications. Irrigation treatments including 100, 75 and 50 percent of water requirement and salinity treatments were 0.7, 4, 8 and 12 dS m-1. Salinity treatments were obtained by mixing fresh water with very salty groundwater. Various forms of production functions such as linear, Cobb-Douglas, quadratic and transcendental were utilized for predicting grain yield. The optimum crop production function was determined by fitting various forms of crop production functions on the obtained data from experiment using SPSS software. For assessing validity of the obtained functions, statistics of mean absolute error, normal root mean square error, determination coefficient, efficiency function and agreement index were used. Thereafter, using the optimum crop production function (quadratic function in this study), optimal depths of irrigation were calculated. Sigma plot software was used for preparing the graphs.
Variance analysis results showed that the combined effect of drought and salinity stress was significant on all of the measured traits except plant height and biomass at one percent probability level (P<0.01). The results also showed that the final rank of quadratic function was better than the other functions. Therefore, it can be concluded that quadratic function is the best crop production function for predicting the yield and yield components of safflower under drought and salinity stress. In all of the irrigation treatments, grain yield reduction gradient was higher by changing the salinity level from 0.7 to 4 dS m-1 compared to changing of it from 4 to 8 and from 8 to 12 dS m-1. Optimal irrigation depths for witness treatment (i.e.irrigation with nonsaline water) in land constrain, water constrain, maximum irrigation depth and equivalent maximum irrigation depth were 142.6, 149.7, 258.2 and 142.4 mm, respectively.
As the experimental and field data, combining the effect of salinity and drought stress, on yield and yield components of safflower are rare, in this study quadratic function as the best crop production function for estimating yield and yield components of safflower is recommended. However, the obtained quadratic coefficients may be site specific and site condition (due to the soil type and the pot planting condition), thus these coefficients may not usable for field conditions. Therefore, it is recommended that more comprehensive studies are done for obtaining the quadratic coefficients of safflower in the field conditions by changing quantity and quality of irrigation water.