Zinc nutrition affects alfalfa responses to water stress and excessive moisture

The interactive effect of applied zinc (Zn) and soil moisture on early vegetative growth of three alfalfa (lucerne) (Medicago sativa L.) varieties was investigated in a sand-culture pot experiment to test whether there is link between Zn nutrition and soil moisture stress or excessive moisture tolerance in alfalfa plants. Three varieties (Sceptre, Pioneer L 69, and Hunterfield) with differential Zn efficiency (ability of a variety to grow and yield well in a Zn deficient soil is called a Zn-efficient variety) were grown at two Zn levels (low Zn supply: 0.05 mg Zn kg-1 of soil, adequate Zn supply: 2.0 mg Zn kg-1 of soil) and three levels of soil moisture (soil moisture stress: 3% soil moisture on soil dry weight basis; adequate soil moisture: 12% soil moisture on soil dry weight basis; excessive soil moisture: 18% soil moisture on soil dry weight basis) in a Zn deficient (DTPA Zn: 0.06 mg kg-1 soil) siliceous sand. Zinc treatments were applied at planting, while soil moisture treatments were applied three weeks after planting and continued for two weeks. Plants were grown in pots under controlled temperature conditions (20 degrees C, 12 h day length; 15 degrees C, 12 h night cycle) in a glasshouse. Plants grown at low Zn supply developed Zn deficiency symptoms, and there was a severe solute leakage from the leaves of Zn-deficient plants. Adequate Zn supply significantly enhanced the leaf area, leaf to stem ratio, biomass production of shoots, and roots, succulence of plants and Zn concentration in leaves. At low Zn supply, soil moisture stress and excessive moisture treatments significantly depressed the shoot dry matter, leaf area and leaf to stem ratio of alfalfa plants, while there was little impact of soil moisture treatments when supplied Zn concentration was high. The detrimental effects of soil moisture stress and excessive soil moisture under low Zn supply were less pronounced in Sceptre, a Zn-efficient alfalfa variety compared with Hunterfield, a Zn-inefficient variety. Results suggest that the ability of alfalfa plants to cope with water stress and excessive soil moisture during early vegetative stage was enhanced with adequate Zn nutrition.