Hydrologic consequences of intensive rotation grazing

Abstract

A four-part study was conducted at the Texas Agricultural Experiment Station, 56 km southwest of Sonora, Texas on the Edwards Plateau. The objective of the study was to provide a greater understanding of the hydrologic impact of high-density livestock activity under a system of short-duration grazing. The research tested the hypothesized beneficial effects of "hoof action" or "herd effect" on hydrologic response as espoused by proponents of intensive rotation grazing systems. In the first phase of this study, no significant differences attributable to stocking density were evident in terms of infiltration rate or sediment production between pastures representing equally stocked 7-, 9-, and 14- pasture short-duration grazing systems. Livestock impact, in terms of AUD's/ha, was identical between pastures. The only difference was the number of days over which the impact occurred and the length of the subsequent rest period. The difference was minimal, however, because the number of pastures was large based on the length of the rotation cycle. The potential for lengthening the period of rest is minimal where the number of pastures is large. The results imply that very little, if any, hydrologic benefit can be expected by large increases in the number of pastures. The second part of this study demonstrated that infiltration rate declined and sediment production increased immediately following short-term high intensity impact of livestock in a short-duration grazing system. The deleterious effect was significant during periods of drought and winter dormancy but not during seasons of active growth. The data indicate that very little potential exists for increasing stocking rates under intensive rotation grazing, particularly where the growing season is short or unpredictable. The effect of livestock trampling on a bare soil surface was evaluated in the third phase of research. In filtration rate declined significantly and sediment production increased significantly following trampling at any stocking rate typical of a short-duration grazing system. The deleterious effect increased as stocking rate increased. Damage was augmented when the soil was wet at the time of trampling. Based on the results, it appears that intensive rotation systems are least suited for arid, semi-arid, or disturbed temperate areas where vegetation is sparse...