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Saving for a Rainy Day

Posted Sep. 1, 2000

It may seem a little odd to talk about how to capture rainfall when it is once again the driest part of the year. I know that we can't manage nonexistent rain, but we should be planning for when the rains do come.

We can't control the amount or timing of rain. But by managing the land, when it does rain we can capture as much as possible to grow grass and recharge ground water instead of letting it run off onto the neighbor's place, carrying our soil with it.

There are many factors that determine how much water the ground can capture, and the one that affects infiltration the most is soil type. Soils are made up of tiny particles whose size determines the general soil texture (sand, silt or clay). Sand particles are large and cannot get very close together. Clay particles are small and can pack tightly together. But the real concern, relative to infiltration, is the amount of space between those soil particles (soil pores).

Raindrops fall like little torpedoes. If the drops hit bare ground, the impact causes an explosion that sends soil particles flying through the air. Those particles land, filling in the soil pores and capping off the surface layer; therefore, no more water gets in. To increase the amount of capturable water, we must protect the soil surface. If the raindrop hits vegetation before it hits the soil surface, a process referred to as interception, it loses a great deal of its energy and will damage the soil surface less. The taller the vegetation, the more likely it is to intercept the rainfall.

So if we manage for increased infiltration, more water is available for the plants and more grass may grow. If we leave sufficient cover, the cycle continues. If cattle graze the grass too short, not only does the ability of the grass to regrow decrease, but also interception decreases and bulk density probably increases, both of which decrease infiltration. Not as much water gets into the soil, and the cycle continues to deteriorate until something happens to change it.

How much cover do we need to leave? That is the magic question. If there is too much cover, even though infiltration is good, the amount of potential production decreases because plants have to compete for light, and grass that could have been eaten is wasted. Different plants provide different amounts of ground cover and can withstand different amounts of grazing. Everyone's pasture is unique, and decisions about how much to graze and how much to leave must be made for each situation.

Management must look beyond what grass could be grazed today and consider how it can be managed to help produce more grass after it rains.

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