Changes in Alfalfa (Medicago sativa L.) Growth and Biochemical Traits in Response to Silicon Application under Different Irrigation Regime

To decrease adverse effects of water deficit is foliar application with chemical agents such as silicon. However, there is low information on the influence of silicon on alfalfa under drought stress conditions. Thus, the current study was conducted to assessment the effect of different silicon concentrations (0, 1 and 2 mili Molar concentration) on alfalfa growth trend and biochemical traits, which grown under five level of irrigation regimes (100% as control, 85%, 70%, 55% and 40% field capacity; FC) according factorial experiment based on completely randomized design with four replication. The results showed that plant height, dry weight, chlorophyll a and b were reduced in response to water deficit; while water deficit increased chlorophyll a to b ratio as well as activity of superoxide dismutase and catalase in alfalfa crop. Also, water deficit up to 55% FC increased leaf silicon concentration, free proline, total soluble protein and peroxidase; however, severe water stress reduced them. Despite negative impact of water deficit, silicon application increased plant height, dry weight, soluble protein and three antioxidant enzymes as well as leaf silicon concentration. The positive effect of silicon on the most of the measured traits was greater at 2 mM than 1mM concentration, which might be due to higher silicon absorption at higher concentration. Alleviation ability of silicon was greater under severe water deficit compared to no or light water stress conditions. Our results suggested that although water deficit reduced growth and caused some changes in biochemical traits; silicon application, especially at 2mM concentration can be advised to alleviate some of the negative impact of water deficit.