Maximizing Limited Rainfall for Forage Growth

In nature, there is a water cycle where moisture goes into clouds by evaporation from moist soil, and/or water surfaces (oceans, lakes, etc.) and by transpiration from plant (evaporation of water from the leaves of a plant). Rainfall from these clouds to the ground returns water to the earth's surface. Rainfall can either go into the soil, or run off the soil surface into creeks, rivers, lakes, and eventually the ocean. Water going into the soil profile refills soil pores. Soils saturated with water will allow excess to percolate through the soil into groundwater or aquifers, or drain into natural waterways. The rainfall held in the soil profile is the water used for forage plant growth and production.

Although in a drought there is a need for rainwater runoff into tanks and lakes for animal drinking water, most rainwater is needed in the soil for plant use. Even though we cannot control the amount of rainfall we get in a drought year, we can affect how much limited rainfall goes into the soil. We can also manage to reduce soil evaporation, which will hold soil moisture for a longer time, hence maximizing the rainfall's usefulness for plant growth.

Research has shown that dry soil without mulch or ground cover does not absorb rainfall readily. Bare, dry, compacted soil will only allow from 5% to 25% of rain to go into the soil profile. Infiltration rates vary with rate and duration of rainfall. The other 75% to 95% is runoff. Soil with a fair ground cover (35% plants and litter) will allow about 85% percolation and only 14% runoff. Soil covered with 60% to 75% grass plants will allow 98% soil percolation and only 2% runoff from moderate rains. When you compare soil covered with grass plants with good root systems and brush or weeds, grass will allow much more of the rainfall to go into the soil profile. Controlling cedar brush in Central Texas and replacing it with desirable grasses allowed six times more water to percolate into the soil profile than soil covered with cedar. Forage crops also provide mulch and cover over the soil which minimizes evaporation or soil water losses after a rain. Weed control, brush control and keeping grass plants vigorous in the good years through proper management can make a big difference in subsequent drought years.