Effect of Irrigation Frequency and Environmental Parameters on Transpiration Rate, Leaf Temperature and Growth of Alfalfa under Arid Conditions

Abstract

The effect of two irrigation treatments on leaf transpiration rate (TR) and leaf temperature (LT) of alfalfa (Medicago sativaL.) was measured on a daily and seasonal basis. The treatments consisted of two different irrigation frequencies ; Normal (N: every other day irrigation) and Frequent (F: everyday irrigation). The effect of irrigation frequency on TR and LT was much greater in April and August than in November and January. TRn on a non-irrigated day was lower than TRf reflecting soil water status in April and August. The maximum difference in LT (Ltn-LTf) was 4°C and 6°C in April and August, respectively. Both plant height and total dry yield were 10% higher in the F treatment than in the N treatment, which was attributed the difference in TR and LT. Estimated transpiration amount of the N alfalfa (TAn) was smaller than that of the F alfalfa (TAf) on the non-irrigated day. The ratio of TAn to TAf was 77%, 72%, 70% and 92% in April, August, November and January, respectively.
Linear regression models of TR with several independent parameters such as quantum (QU), vapour pressure deficit (VPD), relative humidity (RH), leaf temperature (LT) and chamber temperature (CT) were established for the F alfalfa. QU had the highest positive correlation with TR among these parameters. A separate experiment, in which different light intensity treatments were established, also showed good correlation between these two factors.