Find and remove impediments to water movement to prevent crops from going thirsty
We all know water flows—through rivers and down sloping surfaces. But here’s a new way to think about water movement. In ideal conditions that produce healthy yields, water continually flows through your plants.
As a farmer, you want to keep that water moving—from rainfall or irrigation, into the soil, then to your crop’s roots and upward. Any barrier that impedes water movement jeopardizes yield. So, you must identify the barriers and figure out how to remove them.
“The ability of water to infiltrate and move through soil varies by soil texture—sandy soil versus heavy clay, for example,” says Farm Journal Field Agronomist Ken Ferrie. “You can’t change a soil’s natural texture (sand, silt or clay), but you can help water move as efficiently as possible through any soil, even difficult ones, by removing barriers to water movement.
“Impediments to water movement can occur at the soil surface or deeper in the soil profile,” Ferrie continues. “At the surface, crusting or sealing caused by heavy rain can reduce or prevent water infiltration. Beneath the surface, water movement can be impeded by soil density changes and compacted layers.
“Some density changes occur naturally. For example, differences in bulk density between the A and B horizons result from how the soil was formed. The two horizons may go from higher to lower density or vice versa. But density changes also can be caused by horizontal tillage.
“Compaction is usually man-made, caused by heavy equipment, often operated when the soil is wet. The closer to the surface a density change occurs, the more expensive it is in terms of reducing yield because it results in less total area for water storage, microbial activity and root growth.”
The first step to improve water movement is to dig a soil pit in each management zone of every field and see if you have a water impedance problem. You can spot soil density changes and compaction by differences in soil moisture above and below the layer and by crop roots growing horizontally, rather than vertically, when they encounter the dense layer, Ferrie says.
If you find obstacles to water movement, the next step is to figure out what caused them. Then you can choose the right tool, depth and horsepower to remove the obstacles. If you use the wrong tool or depth, you might waste time and fuel and even make the situation worse.
“When removing a dense layer, your tillage tool must reach a couple inches below the restriction,” Ferrie says. “I’ve seen farmers try to take out a dense layer 8" below the surface with a chisel plow that ran only 6" deep. Not only did they fail to remove the dense layer, but they also loosened the soil just above it. That created a greater contrast in density, which made the problem worse. In addition, if the soil slopes a bit, the situation can lead to severe rill erosion. Soil can erode right down to the original dense layer.
“If you have a field cultivator layer 3" or 4" deep, a chisel plow might fix it. But if you have a plowsole at 6" to 7", you might need a disk ripper to take it out. If deep tillage is needed, make sure you have a big enough tractor to pull the implement at the desired depth.”
Conversely, Ferrie has seen farmers disk-rip 12" or 13" deep when the dense layer was only 4" below the surface. “In that situation, you can bury too much residue,” he says. “With no surface cover remaining, you expose the soil to erosion. The first hard rain might destroy surface structure, seal the surface and prevent water infiltration for the rest of the season.”
In all barrier-removal situations, your goal is to replace a shallow, horizontal rooting environment with a deeper, vertical one. “Maintaining a vertical environment requires strip-till, no-till or other reduced-tillage techniques,” Ferrie says. “Continuing to use horizontal-tillage tools can put the density layer back in.”
Horizontal tools can also create silt layers, another form of density change. “Abrasive tillage can create a water barrier by breaking down the soil’s healthy crumb-like structure and causing sand, silt and clay particles to separate,” Ferrie says. “The coarse particles rise to the top of the profile, and the small silt particles drift down and create a dense layer. In a soil pit, the silt layer usually appears slightly darker.
“You can remove a silt layer with vertical tillage that lifts the silt back into the surface structure and mixes it in,” Ferrie continues. “If possible, add grasses, such as corn, wheat, rye, barley or cover crops, to your rotation. Grass roots produce a glue-like substance that helps build a healthy crumb structure of sand, silt and clay.
“Finally, move away from tools that tear down soil structure, such as moldboard plows and disks. Replace them with a chisel plow, a lifting tool that is less abrasive.
Removing water movement barriers should always follow a systems approach, Ferrie says. Vertical tillage usually is a major component, but other tools include fertility management, crop rotation and cover crops.
Be patient and persistent. “You can fix some density problems fairly quickly. But others, especially soil compaction caused by heavy equipment, might take two or three years,” Ferrie says.
Vertical tillage usually is the first step to remove water-movement barriers caused by soil density changes such as tillage pans and compaction.
Some soils require farmers to take special measures. For example, sloping soil is subject to erosion. “If you can’t do vertical tillage after soybeans without creating an erosion hazard, do tillage following corn,” Ferrie advises. “Or add a second year of corn to your rotation and do the tillage while you have more crop residue to work with.
“Planting a cover crop after you till will protect the soil surface from erosion during the winter and early spring,” Ferrie adds. “If your conservation plan does not allow any tillage at all, plant a cover crop of tillage radishes or deep-rooted ryegrass to put bio-channels through the dense layer.”
Some soils are naturally tight-structured and difficult to move water through. They have high bulk density and few macropores for water storage. Watch for this kind of soil when you acquire new ground, Ferrie warns. The practices you have used on easier-to-manage soil won’t work here. Consult a soil survey and compare the characteristics of your new ground to the soil you’re used to farming.
“Dense layers cost a lot more yield in this kind of soil,” Ferrie says. “It’s even more crucial to develop and keep a vertical environment. But, in this kind of soil, tillage might only help for a few weeks or months. To remove a dense layer in these soils, you must put in bio-channels.
“Two of the best builders of bio-channels are nightcrawlers and earthworms. Nightcrawlers live in deep vertical burrows, which leave bio-channels. Nightcrawlers are active in soil with a pH in the 6.2 to 6.5 range. Leave residue on the surface for them to eat. Nightcrawlers and earthworms need oxygen, so if the soil is poorly drained, add drainage.”
Bio-channels also include old root channels. “To preserve bio-channels, take tillage out of your program,” Ferrie says. “To add more, plant cover crops.”
In summary, keep water moving by identifying barriers in the soil. Determine their cause and how to fix them. Your water management plan should include tillage to remove dense layers; reduced tillage to put the soil back into a vertical format and maintain bio-channels; and residue on the surface to protect it from heavy rains.
Poor Drainage Limits Water Movement
Although it might seem contradictory, a lack of soil drainage forces farmers to use practices that build barriers to water movement. “Often, poor drainage sets in motion a chain reaction that makes a bad water movement situation worse,” says Farm Journal Field Agronomist Ken Ferrie. “Poor drainage delays all spring operations—fertilizer and herbicide application and planting. The pressure to plant on time forces farmers to work their soil wet, which creates compaction. Those dense layers restricts earthworms and plants from building bio-channels. The lack of channels reduces the depth of rooting.”
Reduced tillage techniques, such as no-till and strip-till, which are required to eliminate water-movement barriers, make drainage even more important. “Leaving crop residue on the surface reduces evaporation in the spring,” Ferrie says. “But you no longer can use tillage to dry out fields for planting.”
Unmanaged irrigation can create problems similar to poor drainage, Ferrie adds. “Don’t apply water faster than the soil’s infiltration rate,” he cautions. “If you do, it will pond and run off. Irrigate in a timely fashion, so you don’t develop a dry area between the applied water and the water in the soil profile. As water molecules move upward through the plant and exit through the stomata, they pull more water molecules from deeper in the soil, using processes called adhesion and cohesion. If the two water ‘fronts’ are allowed to separate, water will no longer be pulled upward from the deeper profile.”
The Chemical Aspect of Water Management
Besides its physical (soil structure and compaction) and biological (nightcrawlers, earthworms and cover crops) components, water management also has a chemical aspect: pH and calcium.
“Soil pH affects the microbial population, which is a huge factor in building soil structure,” says Farm Journal Field Agronomist Ken Ferrie. “Calcium is required to flocculate clay particles—or hold them together. It is essential for building a healthy crumb-like structure, which permits water storage and movement. If pH is out of whack or calcium content is too low, you will not be able to correct problems.
“Fortunately, the chemical aspect is one of the easiest things to fix,” Ferrie says. “But if you don’t follow a good soil testing regimen, you might miss it. You can’t see low pH or calcium just by looking at soil.”
As a limited yet vital input, water demands a high level of diligence. The Water Management series details how farmers can manage earth’s most valuable resource to boost yields and profit.