I recently had a conversation with a retired farmer, and he commented that his fields seem to have more runoff and water erosion then he’s ever seen in the past 40 years he farmed the ground. He went on to say that this climate change thing everyone is talking about might be the cause of getting these heavier rainfall events that the soil just can’t absorb.
Not wanting to offend my friend I half-heartly agreed with him even though I knew there was more to the story. What wasn’t mentioned during the conversation was that his current tenant, like he did for the last forty years, is using a very intense tillage system with long periods of fallow. My suspicion is this likely is the main contributing factor to the runoff and erosion issue.
Soil water infiltration is influenced by several things. Different soil types can make a big difference. Water will move more quickly through a sandy soil, where there are large pore spaces, than in a clay soil where pore spaces can be very small, especially in degraded soil that has no structure or aggregation. On the other hand, clay soil tends to shrink and crack when they dry, which allows a direct conduit for water to enter the soils.
But how the soil is managed also plays a big role in how much water infiltrates into the soil.
Keeping the soil covered, either with crop residue from the previous crop, or with a crop canopy helps with infiltration by reducing the direct impact of the raindrop.
If the raindrop hits the soil directly it tends to dislodge and break down soil particles which leads to the soil surface crusting and seals it off, which doesn’t allow any additional water to soak in. If there is something to intercept the rain drop, like residue or canopy, this will slow the rain drop down and reduce the force of the impact to the soil surface. This allows more water to enter the soil before it begins to runoff. Keeping the soil covered also helps with evaporation losses, which in our part of the world is a huge water loss.
Having stable soil aggregates also plays a key role in water infiltration. A soil aggregate is basically a bunch of individual soil particles of sand, silt and clay being held together by what I call biological glues. These glues are produced and secreted by soil microbes that live in the soil. These microbes rely on a living plant for their livelihood, so when a field is fallowed for a long period of time microbial life in the soil is significantly decreased.
Excessive tillage can also be detrimental to beneficial soil microbes. If it doesn’t just kill them outright it will certainly destroy the habitat that they live in.
Soils with good aggregate stability, provide bunches of pore space for water to enter and be held in the soil. Kind of like the difference one jar filled with gravel and another one filled with clay. The jar that has the gravel will hold a lot more water because the larger and more abundant pore spaces.
So how do we increase infiltration rates? The short answer is to reduce tillage and shorten fallow periods the extent that the climate will allow.
I understand this is a hard sell in western Kansas on dryland cropping systems, and even more so when we are in the middle of a prolonged drought. But if the weather and weed pressure allows an opportunity to shorten up the fallow period by slipping a cash or cover crop in the rotation, or if a tillage pass or two could be eliminated, it would certainly increase the opportunity to capture more water in the soil.
For more information about this or other soil health practices you can contact me at [email protected] or any local NRCS office.
Dale Younker is a soil health specialist at the Natural Resources Conservation Service in Jetmore.