Rainfall is a major limiting factor for livestock production from Texas rangelands. Everything from attempts by self-professed "rainmakers" to new technologies such as cloud seeding has been tried to improve the quantity and predictability of precipitation. All such attempts have generally ended in failure.

Technology cannot predictably manipulate the weather. However, management tools are available to improve the effectiveness of any rainfall received. To properly use and benefit from these tools, you must first understand how soils, vegetation and livestock influence water use on rangeland.

An approximate use of water on rangeland is shown in Figure 1. Actual water loss values vary depending on factors such as the seasonal pattern of annual rainfall, individual storm intensity and duration, type and condition of the range site, etc. During rainfall, water may enter the soil surface (infiltration) and move through the soil profile (percolation) or runoff the soil surface to be lost down creeks or draws. Most ranchers desire to minimize rainfall runoff in order to maximize rainfall effectiveness for livestock production. Research indicates that the relative quantity of runoff is directly related to the vegetation characteristics of the site. The differences in runoff between vegetation types in the Edwards Plateau region of Texas are shown in Figure 2. Sites dominated by plant species that provide good ground cover hold rainfall on the pasture better. Thus, sites dominated by oaks or bunchgrasses lose very little precipitation to runoff. On the other hand, sodgrasses or bare ground do not provide sufficient plant or litter cover (decomposing plant material) to effectively facilitate infiltration. Runoff and soil loss from these areas may be great. Heavily grazed watersheds on the Sonora Agricultural Experiment Station have a runoff rate approaching 10 percent of annual precipitation (Smeins, 1977). In the example presented in Figure 1, a 10 percent loss of precipitation as runoff equates to 2 inches of water annually. [Next Page]