Optimal coupling combinations between the irrigation rate and glycinebetaine levels for improving yield and water use efficiency of drip-irrigated maize grown under arid conditions

This study was conducted over 2 years (2011 and 2012) to determine the optimal combinations between the irrigation rate and glycinebetaine (GB) levels in order to maximise yield and irrigation water use efficiency (IWUE) for drip-irrigated maize. A field experiment was performed using a randomised complete block split plot design with three drip irrigation rates (I1: 1.00, I2: 0.80, and I3: 0.60 of the estimated evapotranspiration, ET) and five GB levels (GB0, GB25, GB50, GB75 and GB100, GB levels at 0, 25, 50, 75 and 100mM, respectively) as the main and split plots, respectively. We found that although exogenously applied GB appeared to have different effects on yield variables and IWUE, these differences were dependent on the level of GB within the same irrigation rate. The grain yield and yield component values for I2GB50 treatment were occasionally comparable to those obtained for I1GB0 treatment, and the values for both treatments were higher than those obtained for I1GB75 or I1GB100. I3GB50 or I3GB100 had grain yield and yield component values similar to those obtained for I2GB0 and I2GB100. The highest value for IWUE was found for I2GB50 and this value was similar to that obtained with I3GB75, while the lowest values were obtained for I1GB75 or I1GB100. Medium GB levels were effective under I2 and I3 treatments to obtain the lowest value for seasonal yield response factors (ky). The production functions of yield versus GB levels were second-order relationship for all drip irrigation rates. In conclusion, exogenous application of GB has the potential to improve yield and IWUE under limited water application, while a threshold level of GB was required for a positive effect.