Water Usage of Certain Native Grasses in Prairie and Pasture

Abstract

A study of water content of soil covered with prairie vegetation and the same soil, a few yards distant, with grazed prairie usually reveals considerable difference in the amount of water at various depths to several feet. 'This was shown by soil sampling from Iowa to Kansas during spring and summer of 1939. Greater foliage area of the ungrazed cover causes greater water loss by transpiration, but the protection of the soil from direct insolation results in lower evaporation. Decrease of cover under grazing lessens transpiration and accelerates evaporation from the soil surface. The greater cover in ungrazed prairie, moreover, greatly decreases through rainfall interception the amount of water supplied to the soil (Clark, '40), while trampling in pasture makes the soil less receptive to water infiltration and promotes runoff (Weaver and Noll, '35). Numerous other factors are concerned. Since water content of soil has become a problem of ever increasing importance during drought, it was decided to devise an experiment whereby the water losses from a soil clothed with grazed and ungrazed grasses of several species common to true prairie could be measured directly. A knowledge of the water requirement of the same species in undisturbed prairie and under simulated grazing (clipping) would only partially solve the problem of water usage, because grazing so greatly influences s u r f a c e soil evaporation. Water requirement is the ratio of the weight of water absorbed by a plant during its growth to the weight of the dry matter produced, exclusive of roots (Briggs and Shantz, '14), while water usage designates the quantity of water used by plants in producing a unit of dry matter, exclusive of roots, plus the amount lost by evaporation from the surface of the soil occupied by them during their period of growth. Most experiments on water requirement have dealt almost entirely with cultivated plants and not with native species (Briggs and Shantz, '13, '14; Montgomery and Kiesselbach, '12; Kiesselbach, '16; Miller, '23; Shantz and Piemeisel, '27; and Dillman, '31). A notable exception is the study by McGinnies and Arnold ('39) on range plants of Arizona. The entire water loss including both transpiration and surface evaporation from soil areas supporting alfalfa, greasewood, and salt grass has been determined experimentally by White ('32). Blaney ('33), working in California, determined the use of water bv salt grass and Bermuda grass, particularly with reference to the depth of the water table. His research also included water usage of cattails, tules, and wire rush. Water usage of intermixed grasses and forbs of true prairie has been determined by Flory ('36), Fredricksen ('38), and Noll ('39), the last two investigators working during years of extreme drought. Few other studies on water usage of native plants are known to the writer.