Partial root zone drying irrigation, planting methods and nitrogen fertilization influence on physiologic and agronomic parameters of winter wheat

The effectiveness of water-saving irrigation strategies such as partial root zone drying (PRD) should be explored to ensure food security as the availability of water for irrigation declines and population increases. PRD is easily performed by localized irrigation method; however very small percentage of irrigated area is under this irrigation method and main irrigation method is furrow irrigation that should be adapted to PRD. In this respect, present study was conducted to explore the effects of PRD in furrow irrigation strategies on physiological and agronomic behavior of winter wheat. The field experiment included two irrigation strategies (variable alternate furrow irrigation (VAFI) as PRD and ordinary furrow irrigation (OFI), two different planting method (in-furrow planting and on-ridge planting) and three nitrogen rates (0, 150, and 300 kg N ha(-1)) over 2015-2016 and 2016-2017. Results showed that decreasing leaf water potential (LWP) during the stem elongation stage resulted in increasing the sensitivity of winter wheat to water stress and yield reduction. The leaf photosynthesis rate (A(n)) was not significantly lowered in VAFI (PRD) in comparison with that obtained in OFI. The VAFI strategy reduced the stomatal conductance (g(s)) about 12% and 7% in comparison with that obtained in OFI in the first and second year, respectively that were statistically significant. The lower slope of linear relationship between leaf transpiration efficiency (A(n)/T-r) and vapor pressure deficit (VPD) in VAFI strategy indicated that with increasing VPD, leaf transpiration efficiency was higher than that obtained in OFI. As a consequence, VAFI strategy as PRD was effective in increasing A(n)/T-r and can be an alternative irrigation management in winter wheat farms with limited water supplies. Although, in-furrow planting showed higher efficiency in increasing yield in comparison with that obtained in on-ridge planting, on-ridge planting showed higher effects on leaf transpiration efficiency. Furthermore, there was no significant difference between two application rates of nitrogen (150 kg N ha(-1) and 300 kg N ha(-1)) for different parameters; therefore, application of 150 kg N ha(-1) can be suggested as an effective rate to increase winter wheat yield. Consequently, in areas with scarce water and furrow irrigation, combination of VAFI, in-furrow planting and 150 kg N ha(-1) is recommended to achieve optimum yield with possibility of saving water during the winter wheat growing season.