So if technology cannot turn on the water from the sky when we need it, we have to look at management tools that can improve the effectiveness of rainfall events when they do occur. Research has shown that the amount of rainfall runoff from a particular range site is directly related to vegetation on the site. Generally speaking, sites that are dominated with plants that provide good ground cover hold rainfall on the site the best. In contrast, sodgrasses or bare ground do not provide sufficient plant litter cover to allow for effective infiltration of the rainfall, thus we see heavy runoff and soil loss.
Evaporation is another source of water loss on our rangelands. The amount of water lost through evaporation from the plant canopies or soil surface is related to the intensity of the rainfall event and the weather conditions that follow the event. As you move west in our state, this evaporation loss increases.
We know that not all plants found on our rangelands are desirable for livestock and wildlife production. Brush or toxic and /or noxious weeds deplete water that could be used for more desirable species.
So with these factors in mind, here are some tips to help improve rainfall effectiveness on our rangelands. First we should work on reducing runoff, as this can represent a serious loss of water from our ranch. Research has shown that rangeland infiltration rates generally increase as total plant cover increases. The plant cover slows the water movement across the soil surface allowing more time for water to infiltrate before being lost down creeks and draws. Plant cover also protects the soil surface from rain drop splash. Vegetation type also affects runoff. Bunchgrasses are more effective at reducing runoff than sodgrasses, while Oak mottes produce even less runoff. Livestock stocking rates, grazing systems, and species of livestock are all major management tools that can be used to manage the range forage base as well.
Another important factor to improve rainfall effectiveness is reducing the undesirable weed and brush species. It has been estimated that mesquite uses 100 gallons of water for each pound of above ground plant growth produced. Perennial grasses are more efficient users of water requiring from 40 to 75 gallons of water for each pound of above -ground biomass produced. The amount of water used by unwanted plants can vary greatly from ranch to ranch depending on the species of plants present and their density. Having a plan to manage these undesirable plants can help improve the efficiency of water use for livestock and wildlife.
The harvest of vegetation by livestock must be limited to ensure regrowth and reproduction of perennial range vegetation. An old rule of thumb goes something like this, 50% of forage should be left standing for health of the plant, 25% will be lost to trampling, weathering, or consumption by insects and small mammals, which leaves only 25% that is actually consumed by livestock. For most of us, that means we should have reduced stocking rates a long time ago.
Bottomline, rainfall represents the single most limiting factor to livestock production on our Texas rangelands. We have to do the best job possible at managing these range sites so that when we are blessed with a rainfall event, our rangelands can take full advantage of that precious water resource and keep it on site, and store in the soil profile, for the dry times that will come again.
