The effect of soil moisture on consumptive water-use efficiency, root development, and growth components of alfalfa (Medicago sativa L.).

An experiment at Tucson, Arizona determined the consumptive water-use efficiency of four alfalfa (Medicago sativa L.) cultivars grown under three irrigation regimes. Two additional experiments investigated relative growth rates of roots and shoots and anatomical features of seedling alfalfa roots. Significant differences in dry forage production and consumptive water-use efficiency were found between cultivars, harvests, and irrigations. More forage was produced under the medium regime (irrigated when 70% of available soil moisture was depleted to a depth of 91.4 cm) than under high and low soil moisture levels. The highest forage yield occurred during the second harvest (June 10) and the lowest during the seventh harvest (October 29). The most efficient water-use was obtained when alfalfa utilized 90% of the available soil moisture in the upper 1.21 m prior to irrigation. Differences in the leaf/stem ratio, specific leaf weight, and leaf area index were found between harvests while no differences were found between cultivars and irrigation regimes. Differences were found between the dry weight production of roots and shoots of seedling alfalfa grown under three moisture levels. No significant differences were found in the number of xylem elements and per cent of the root that" was vascular cylinder.hydrology collectio