Adjustment of radiation use efficiency of winter wheat by air temperature at different irrigation regimes and nitrogen rates

Abstract

In this research, radiation use efficiency (RUE) of winter wheat was determined under different irrigation regimes and nitrogen application rates in experimental field at southwest Iran (semi-arid region) in 2009–2010 and 2010–2011. The experiment was laid out as a split plot design, with irrigation treatments as main plots and N fertilization as sub-plots with three replications. Irrigation treatments were 1.2 (I4), 1.0 (I3), 0.8 (I2), and 0.5 (I1) times of the full irrigation requirements and N treatments were 0 (N1), 46 (N2), 92 (N3), and 136 (N4) kg ha⁻¹. Air temperature had significant effects on RUE that was adjusted by multiplication of hourly temperature factor to the hourly values of solar radiation (RUE _a ). The values of RUE _a were significantly different from the values of RUE in both growing seasons. The values of RUE _a ranged from 1.44 to 1.83 g MJ⁻¹ and 1.45 to 1.81 g MJ⁻¹ in 2009–2010 and 2010–2011, respectively. In both growing seasons, minimum and maximum values of RUE were at I1N1 and I4N4 treatments, respectively. The methods of daily maximum and minimum air temperature were modified for considering the effects of air temperature on RUE at locations where hourly air temperature and radiation were not available.

Keywords:

• air temperature
• irrigation regimes
• applied nitrogen
• radiation use efficiency
• winter wheat

Acknowledgments

This research was supported partly by a research project funded by Grant nos. 91-GR-AGR 42 and 91-GR-AGR-40 of Shiraz University Research Council, Drought National Research Institute, and Center of Excellence for On-Farm water management. Further, scholarship granted to the first author by Higher Education Ministry of I.R. of Iran is acknowledged.