What Kind of Water Bucket Is Your Land?
By Nathan Haile, USDA NRCS state soil health specialist
Producers may not realize that their largest water “storage facility” or “bucket” is actually the land they manage. When we talk about water management on a farm or ranch in Texas, the first item of business should be to capture as much precipitation as we can in that environment. I’ve often heard great ranch managers say, “Drought doesn’t degrade the land. The manager’s decisions during the drought destroy the land.” They are right! Droughts and floods have been around forever and will continue in our future.
The bucket, often referred to as the available water holding capacity (AWC), is determined by many factors, including inherent soil properties and dynamic soil properties. Inherent soil properties that affect water-holding capacity include characteristics like soil texture (percent sand, silt, and clay), and solum depth (the depth from the soil surface to the geologic material like bedrock or shale). Although these factors are important and should be studied by landowners and managers, I want to focus on the dynamic soil properties.
Dynamic soil properties are characteristics that change on a constant basis, depending on the environment we are provided and the way we treat the soil. We can’t control when or how much it rains, but proper management of the dynamic soil properties will control how much we “capture” or how much we “shed.” Is your operation full of water catchments or watersheds?
The properties we can enhance include infiltration, aggregate stability, structure, porosity and organic matter. These are just a few of the dynamic properties evaluated in soils but are the primary properties when it comes to water management.
Infiltration
Many times when we get a 3- to 4-inch rain, we are only able to capture 30 to 40 percent, because we lack the vegetative cover needed to intercept the raindrop and move it slowly to the soil surface.
The raindrop impact on the bare ground is severe and can displace soil particles, creating a seal. The water, in turn, runs down slope instead of entering the soil profile. Aggregate stability has a major influence on infiltration.
Aggregate stability
Once the raindrop gets to the surface, the aggregate stability of the soil (basically the rating of the soil’s ability to withstand water gushing into the micro-pores) determines how well the water percolates into the topsoil. Aggregates form from soil microbes consuming plant material and other matter and excreting biologic glues that bind the soil particles into strong aggregates that withstand the force of water entering the soil.
Structure
There are 7 structures often found in Texas soils. Granular (also known as crumb), subangular blocky, blocky (think of an ice cube), prismatic, columnar, platy and massive (think of an asphalt parking lot).
Yes, prisms, columns and plates — they look like they sound. Air, roots and water can move through prisms and columns well, but will puddle or move horizontally on the plates instead of penetrating the soil.
Subangular blocky and blocky have moderate movement of air and water, while massive is severely limiting. Land managers should be working towards crumb. This granular structure allows movement of water, roots and the much-needed exchange of gasses from the soil environment and the atmosphere above.
The structure is greatly influenced by the soil biology (worms, bacteria, fungi and other bugs) moving in and around soil pores feeding on the plant roots and other dead soil microbes. Plants also release acids that attract microbes, which in turn build aggregates that can form granular structure. Grasses are great at forming aggregates, helping to build the crumb type of structure.
Porosity
Micro- and macro-pores play a vital role in water storage and management in our “bucket.” Imagine a 1 x 4 plank compared to the same 1 x 4 kitchen sponge. Both have pores, but due to its diversity in the size and number of pores, the sponge quickly soaks up and holds the water. The wood allows water to infiltrate slowly and holds very little water.
Porosity is enhanced by a diversity of plant types growing through the year, feeding the soil microbes and creating pores for greater water infiltration when precipitation is received. Taproots can help build macro-pores in compacted soil, allowing water to move into the soil profile quickly during a storm event.
Organic matter
“Miracle of the soil,” this matter can make you sound like a “real salesman.” I often get asked, “How can I resist the droughts?” My answer is organic matter. And when I get asked, “How do I get my soils to take on floods?” My answer is organic matter!
Why? Because organic matter (the carbon from decomposing plant material and decaying micro-organisms) allows for the greatest infiltration and water storage, but also has the greater soil strength, which allows water to move through the soil profile or off the soil surface without detaching the soil particles and causing massive erosion. Organic matter is a slow-building process in a place like Texas, where soil microbes are always at work and the temperatures are severe enough to burn up organic matter quickly. Work to keep vegetative cover at all times and balance that residue between high-carbon straws and low-carbon broadleaves and legumes.
My suggestion is to own a steel-handled sharp shooter and use it often to monitor the dynamic soil properties on your farm or ranch to increase your effective rainfall! ❚
“What Kind of Bucket” is excerpted from the Texas Range Report printed in the May 2017 issue of The Cattleman magazine.