Document Type : Original Article
Author
Associate professor, Department of Agronomy and Plant Breeding, Isfahan (Khorasgan) Branch, Islamic Azad University, Isfahan, Iran.
Abstract
Introduction
Drought is the main cause of wheat yield loss. This fact accompanied with the increased water demand raises the essential question that how the increasing agricultural production can be maintained along with sustained utilization of water resources (Dugan and Flower, 2006). A technique for efficient management of irrigation water is to use new models for determining water demand and scheduling irrigation along with decreasing the susceptibility of wheat to water deficiency and improving their tolerance to drought by breeding. Accordingly, modified Hargraves-Samani equation is more precise than FAO equation for arid and semi-arid regions of Iran (Hargraves and Samani, 1985). Furthermore, given the global validity of Hargraves-Samani model among other models, it can evaluate ET0 more precisely in arid and semi-arid regions. Najafi and Tabatabaei (2004) used the following modified Hargraves-Samani equation in ET-HS model for evaluating evapotranspiration. The objectives of the current study were to determine sound management of water use during sensitive growth stages of wheat and to minimize water use per wheat grain yield and dry matter production.
Materials and methods
In order to evaluate ET-HS model in determining wheat crop water demand in Isfahan, an experiment was conducted at research field of Department of Agriculture, Khorasgan Branch, Islamic Azad University, Isfahan, Iran in 2012. The study was based on a Randomized Complete Block Design with three replications and six treatments. The irrigation treatments included irrigation to supply 50, 75, 100, 125 and 150% of crop water demand on the basis of ET-HS model during growing season and control (conventional irrigation) which was irrigation on the basis of 70 mm evaporation from Class A evaporation pan during growing season. The parameters of ET-HS model used in the current study included altitude from sea level, latitude, actual sunny hours and mean wind speed. The coefficients of the equation of the model were determined and it was calibrated for Khatounabad Region of Isfahan. Accordingly, modified Hargraves-Samani equation is more precise than FAO equation for arid and semi-arid regions of Iran (Hargraves and Samani, 1985). Furthermore, given the global validity of Hargraves-Samani model among other models, it can evaluate ET0 more precisely in arid and semi-arid regions. Najafi and Tabatabaei (2004) used the following modified Hargraves-Samani equation in ET-HS model for evaluating evapotranspiration:
ET(ij)= α j (T max j – T min j) [(T max j + T min j)/2 + 17.8]
where, ET is crop evapotranspiration, α is calibration coefficient (which depends on regional climate and soil conditions) and Tmax and Tmin are daily maximum and minimum temperature. After calibration for a certain region, ET-HS model needs a few simple climatic variables, i.e. minimum and maximum daily temperatures, which are readilyavailable to farmers. In addition, in their studies on tomato and eggplant, Najafi and Tabatabaei (2007) concluded that ET-HS model is quite useful for estimating water demand and for scheduling irrigation. Since sound determination of wheat water demand is very important in planning irrigation management, wheat vapotranspiration models need to be evaluated and if water use is accurately managed, especially during sensitive growth stages, WUE will be improved. The data were statistically analyzed by software MSTAT-C and the means were compared by Duncan test at 5% probability level.
Results and discussion
The results showed that irrigation treatment had significant effects on, number of spikes, number of seeds in spike, thousand seed weight, grain yield, biological yield, harvest index, water used, water use efficiency based on total dry matter and grain yield.
The highest number of spikes, number of seeds in spike, thousand seed weight, grain yield and biological yield was produced by plants irrigated to supply 100% of their water demand. As the water demand percentage were increased, these characteristic. Control treatment did not show significant difference with the treatments of irrigation to supply 100% of crop water demand. Treatments of irrigation to supply 50 and 75% of crop water demand which had the lowest number of spikes, number of seeds in spike, thousand seed weight, grain yield, biological yield did not show significant difference with each other. Therefore, low-irrigation (water stress) resulted in significant loss of these characteristic in both treatments. This response has been confirmed by Liu et al., (2016) .The highest WUE for total dry matter and grain yield were obtained from the treatment of irrigation to supply 50% of crop water demand. It exhibited statistically significant difference with all treatments except control. As the amount of irrigation water was increased, WUE for grain yield significantly decreased. It shows that the increase in grain yield was not able to compensate in increase in the amount of applied water. The lowest WUE for total dry matter and grain yield were obtained from the treatment of irrigation to supply 150% of crop water demand.
Conclusions
On the basis of ANOVA results, irrigation treatment had significant effects on all measured treatments. The highest the number of fertile spike, the number of grain in the spike and 1000 grain weight which was lead to production of the functional rate of seeds and harvest index in comparison with irrigation treatments. Therefore in similar condition with this study, the most suitable irrigation treatment according to the ET-HS model during the growth season is 100% treatment of water requirement.
Keywords
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