GREENHOUSE STUDIES OF THE EFFECT OF CLIPPING THE TOPS OF ALFALFA AT VARIOUS HEIGHTS ON THE PRODUCTION OF ROOTS, RESERVE CARBOHYDRATES, AND TOP GROWTH

Abstract

Alfalfa is frequently used as a pasture crop in the state of Michigan, such use being particularly advantageous during the hot summer period. Grazing of livestock on alfalfa generally removes the upper portions of the top growth of the plant first, the grazing being practically uniform over the entire area. This makes it possible to remove the livestock from an alfalfa field before all of the top growth is consumed, or to stock the area so that the basal portions of the shoots are rarely eaten. Management practices which permit prolonged close grazing frequently result in considerable damage to the stands. In an attempt to determine the amount of top growth necessary to keep alfalfa plants from being weakened, or the reserves of stored food from being depleted, cultures of Hardigan alfalfa plants were set up in the greenhouse at Michigan State College in East Lansing on October 9, 1936. The cultures were grown in quartz sand in 10-inch clay pots from seedling plants collected in the field and transplanted to pots. Eight plants were placed in each pot, and each treatment was replicated five times. All cultures were supplied with the same nutrient solution. On March 29, 1937, the plants had reached the blooming stage and three cultures were photographed (fig. 1), harvested, and the green and dry weights of tops and roots determined. These three cultures were harvested before any cutting treatments were begun and will be known as initial checks. After the roots were washed free of sand a small segment from each of 15 roots was placed in a fixing solution of formalin alcohol to be preserved for histological study of stored starch. The cultures remaining were grouped into lots of 5 and cut weekly from March 31st until May 26th, when the experiment was discontinued. Five cultures were left uncut throughout the duration of the experiment and were harvested when the experiment was completed. These 5 cultures will be known as final'' checks. In the case of the final checks the alfalfa in the greenhouse had reached a condition comparable to that in the field when alfalfa is ordinarily cut for hay. The yield of green and dry weight of tops was determined for each culture within each cutting treatment. The cutting treatments were as follows :