A couple weeks ago I heard South Dakota beef producer Lyle Perman speak about his ranch as a rain management tool.
It's a great concept. Forage is a solar conversion machine, of course, but moisture is the secondary fuel plants needs to function. In light of the ongoing drought I think it's worth recalling a few of Perman's points.
Perman titled his talk, "Managing Three Billion Gallons of Water." He was speaking at the Grazing Lands Conservation Initiative meeting in Orlando, Florida.
Three billion gallons is a reference to the total amount of rain that falls on the Perman ranch in a normal rainfall year. Incidentally, the South Dakota beef producer added, he only got 1.3 billion gallons last year.
The question, Perman says, is how much of what falls can you he capture, hold and therefore make available for the forage to use.
Ultimately, the answer to this question lies in what Allan Savory framed as the ecosystem processes:
1. The water cycle
2. The mineral cycle
3. The solar cycle
4. Community dynamics
Each of these four processes is interrelated. As one improves the others improve. As one declines the others decline, although seldom in same proportion or timeframe.
Perman displayed these examples of old and well-tested data on rainfall runoff and rainfall capture:
He used a 1,380-acre watershed as an example. A 2.1-inch rainfall event falling evenly would provide 78.7 million gallons of water to that parcel of land.
- Under good grazing management, which would have more standing plant material and more thatch on the soil and more root mass in the soil and more active soil biology, the land would release in runoff 9.4 million gallons with a rate of 591 gallons per second.
- Under fair grazing, with more bare ground and less plant material both above ground and below, the land would release 16.1 million gallons as runoff at a rate of 1,436 gallons per second.
Perman quotes Rolf Derpsch, a no-till advocate and soil scientist from Paraguay, who says plant material on the soil surface is the most important factor in catching rainfall and moving it into the soil.
Derpsch says, "Runoff and erosion start with raindrop impact on bare soil surface.
"Soil splash seen on fence posts, or on walls in a field or plot of bare soil, is evidence of the force of large raindrops striking bare soil. Meyer and Mannering (1967) reported that in one year raindrops deliver to an acre of land an impact energy equivalent to 20 tons of TNT.
"The impact of falling raindrops disaggregates the soil into very fine particles, which clog soil pores and create a surface seal that impedes rapid water infiltration.
"Due to surface sealing, only a small portion of rainwater can infiltrate into the soil. Most of it runs off over the soil surface [and] therefore is lost to plants and causes erosion damage when flowing down the slopes."
Then Derpsch adds, "On the other hand, when the soil is covered with plants or plant residues, the plant biomass absorbs the energy of falling raindrops and rainwater flows gently to the soil surface where it infiltrates into soil that is porous and undisturbed. In this way soil cover impedes the clogging of soil pores."
In this description Derpsch is specifically addressing farmed ground, although the processes are the same for a beef producer managing pasture, as Perman notes.
Further, Derpsch only gets at the mechanical action of rainfall on bare soil and doesn't get into the functions of plant and soil health improvement from good grazing management.
Perman says he improves infiltration and all the ecosystem processes through good grazing management using 36 paddocks on 5,000 acres to provide ample recovery time for the forage.
"The biggest problem we have in short-grass years like this is getting the cattle off quick enough to prevent the damage it causes by leaving cattle on those pastures too long."