EFFECT OF SOIL MOISTURE CONTENT AND STAGE OF DEVELOPMENT ON COLD-HARDINESS OF THE ALFALFA PLANT

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Abstract
Alfalfa plants were grown in the greenhouse to three developmental stages, (1) vegetative (48 days old), (2) early bud (62 days old), and (3) 50% bloom (78 days old), hardened and subjected to freezing temperatures in an environmental control chamber. Prior to hardening, the Tormentine sandy loam soil in which the plants were growing was brought to three moisture levels, (1) 25% of field capacity, (2) field capacity, (3) and saturation.Electrical conductivity of plant exudate from top growth of plants decreased during hardening and with freezing. Conductivity of root exudate increased during hardening but decreased during freezing.Plants were rated for freezing damage, immediately after freezing and 10 days later. Recovery was significantly higher for plants grown on soils at held capacity than at saturation. Differences in regrowth between 25% of field capacity and field capacity were not significant. Total available carbohydrate content and etiolated regrowth were also higher for plants grown in soil at field capacity.Saturated soil had an extremely adverse effect on development of cold-hardiness of alfalfa plants as compared with effect of field capacity and 25% of held capacity.Plants that were mature before hardening and freezing were more hardy under field capacity conditions than less mature stages of plants, as shown by weight of aerial and root portions of plants, carbohydrates, conductivity, growth without light, and rating of recovery after freezing.