Growth Response of Alfalfa to Duration of Soil Flooding and to Temperature

Abstract

AbstractAlfalfa (Medicago sativa L.) is very sensitive to excessive soil water, yet few studies have been done under controlled conditions to quantify the extent of this sensitivity. The objective of these studies was to investigate the effect of wet soil conditions on alfalfa production. The growth of roots and tops was determined in a factorial greenhouse and growth chamber experiment with treatments for duration of flooding and temperature. Five‐week‐old alfalfa plants, potted in pasteurized soil, were flooded to the soil surface for 4, 8, 12, 16, and 20 days at temperatures of 16, 21, and 27 C, and for 3, 6, 9, and 12 days at 32 C. Root and top dry weights (DW) of flooded and control plants were measured upon draining. Three weeks after draining, the plants were cut to a 2.5 cm stubble and top DW was measured. After 2 subsequent weeks of regrowth, top and root DW's were again measured.Results demonstrated that root growth stopped during flooding. As measured over the 3 weeks following drainage, the rate of top growth of plants was reduced by 50% with 8 days of flooding at 16 C, 4 days at 21 C, 3 days at 27 C, and 2 days at 32 C. No net top growth occurred during the 3 weeks following drainage in plants flooded for over 14 days at 16 C, 10 days at 21 C, 8 days at 27 C, and 6 days at 32 C. In most cases, the negative response to flooding occurred before the disease Phytophthora megasperma Drechs. is thought to have been able to have an influence. This argues for a physiological as opposed to a pathological basis for the injury.