Effects of Frequent Clipping on the Underground Food Reserves of Certain Prairie Grasses

Abstract

A series of experiments in which true-prairie grasses were clipped at frequent intervals afforded excellent materials for a study of the effects of such treatment upon the food reserves. Two species of Andropogon, at present the most important dominants of true prairie, were employed. A series of quadrats on a north-facing slope in the Belmont prairie at Lincoln, Nebraska, in which little bluestem, Andropogon scoparius, grew in about 70 per cent pure stand, was the source of one lot of underground parts. Those of big bluestem, A. furcatus, were obtained about a mile distant from virgin lowland prairie near the flood plain of Salt Creek. Permanent quadrats were marked out in the spring of 1933. The grasses in some were used for controls; in others they were cut close to the ground (in this manner simulating very closely grazed pastures) six times during the growing season, viz. May 9 and 27, June 25, July 27, August 27, and October 10. During the drought year of 1934 the grasses were clipped only four times, May 15, June 13, July 22, and September 27. Only two clippings were made during 1935, due to a dry spring and extreme drought after midsummer. Control quadrats were clipped once each year in October. The last samples were collected on July 25, 1935, after vegetative growth was completed. Samples consisted of the bases of the culmns of the little bluestem occurring below ground and the roots to a depth of 10 centimeters. Big bluestem has, in addition, pronounced shallow rhizomes, which were also taken to the 10centimeter depth. At each sampling materials were secured from both clipped and control quadrats. These were freed from all soil and other foreign matter and then rapidly air dried. After the first year, especially, the samples from the clipped quadrats represented not the average of the whole quadrat but rather the average of the remaining living plants. For example, one-fourth square meter of a control quadrat furnished an abundance of materials from which the samples for chemical analyses could be taken. A sample from the clipped quadrats required much more area-finally over a square meter to secure adequate materials. Although many plants had died, roots and rhizomes were not taken from these, at least not in quantity, since they were often too fragile to withstand the severe brushing necessary thor-