Studies on the growth of alfalfa and some perennial grasses

Grimm alfalfa was much more resistant to winterkilling than was common alfalfa, especially on plats where the fall growth was removed and on the plats cut at immature stages. The protection afforded to alfalfa plants by even small amounts of late fall top growth has a pronounced influence toward preventing winterkilling. In the first year of cutting the largest yields of hay were obtained from plats cut at tenth-bloom and flower-bud stages. In the second year of cutting the largest yields of hay were obtained from plants cut at relatively mature or full-bloom stages. Encroachments of weeds were greatest where the winterkilling was greatest, combined with cutting at immature stages. It was found that cutting the top growth of plants at relatively immature stages retards root development to a marked degree. Roots of plants cut at immature stages are invariably lower in percentage of dry matter than comparable roots of plants cut at more mature stages. The percentage of total nitrogen and the percentage of reserve carbohydrates tends to be lower in roots of plants cut at immature stages, in contrast to the roots of plants cut at more mature stages of growth. In the spring of the year, roots of alfalfa plants contain little starch and are relatively high in sugars. During the summer, a considerable portion of the carbohydrate reserves in the roots of plants are in the form of starch. At the beginning of winter dormancy roots of plants are relatively high in soluble carbohydrate reserves, while the percentage of starch is less than during the summer. A high content of reserves in the roots and the initiation of new root growth do not seem to occur to any appreciable extent until the rate of growth of the tops is relatively slow. The top growth of alfalfa plants cut at immature stages is appreciably higher in percentage of nitrogen than is the top growth of plants cut at relatively mature stages. There is very little difference between the percentage of reserve carbohydrates in the top growth of plants cut at different stages. Storage of starch does not occur to any appreciable extent in immature top growth of alfalfa. Such storage as was found was made only after the tops were relatively mature. Under dark room conditions, plants will produce top growth that is considerably higher in percentage of nitrogen than top growth produced by plants in the field, as far as these experiments are concerned. In a dark room, plants will produce top growth until the percentage of soluble carbohydrates in the roots becomes very low. In this experiment growth ceased when this concentration was from 3 to 5%. The maximum yields of dry matter per acre from plats of Kentucky bluegrass and redtop were obtained from the plats cut at mature stages. It was found that the removal of the fall growth appreciably lessened the amount of top growth produced in the following season. Within the limits of the experiment, the behavior of the grasses with various cutting treatments was similar to that of alfalfa.