Tillage of the soil is as deeply engrained in the culture of farming as tractor color loyalty or church on Sunday. As the practice was passed down from father to son through history, the “why” followed the practice less than the “how” and today farmers and researchers are reexamining the practices necessary for productive fields.
At a series of three cover crop and soil health-centered workshops across the state, Kansas Grazing Lands Coalition partnered with Kansas Natural Resources and Conservation Service to bring up-to-date soil health information to the field. NRCS regional soil health specialist Doug Peterson spoke about tillage history and new practices moving forward.
“I grew up learning a lot of things that I thought I knew about the soil from my dad,” Peterson said. “We had to till the soil to get rid of weeds, to get water to infiltrate, to get a good seed bed and all of those things.”
Peterson already had almost 10 years with the NRCS under his belt before the first time he witnessed a slake test — a measure of soil aggregate stability where two similar soil types, one an aggregate from no-till soil and one from regularly tilled soil, are submerged in water to demonstrate soil structure.
“It was the most eye-opening experience that I have had in my career, and in my whole life, as far as what I thought I knew about soil,” Peterson said. “There’s so many things about the soil that we’ve been taught that just aren’t so.” While the soils in the test are the same soil type and often taken from closely neighboring fields, there’s a distinct difference between the structure of an aggregate versus a dirt clod.
“A clod is a chunk of soil made up of sand, silt, clay and maybe a little organic matter, but generally a clod to me is something that is formed out of pressure and compaction,” Peterson said. “An aggregate on the other hand is a chunk of soil formed under natural processes — by biology and roots.”
As someone who had been taught soil erosion was based solely on soil type, Peterson said it was a breakthrough for him to step back and see erosion as a function of management.
“Part of that soil productivity and process isn’t just N, P and K, it’s organic matter, biologic activity and aggregate stability,” Peterson said. “I would submit to you that the belief that tillage improves infiltration and all the other things we think are important was based on soil that had that high organic matter, biologic activity and aggregate stability.”
Farmers’ ancestral knowledge of conventional tillage applies to healthy soils, Peterson said. Tilling degraded soils negates a lot of the benefits of tillage.
“A recently tilled perennial grass field is typically high organic matter, aggregate stability and biologic activity, as well as being really productive,” Peterson said. “We know now that that tillage — in the short term — adds oxygen, speeding up the biologic activity and mineralization.”
The benefits of long-term tillage are a fallacy, Peterson said. In early tillage practices, farmers would plow under a field only four to five years before moving to a new location, and those long rotations allowed the soil time to recover.
“We know that long-term tillage burns organic matter,” Peterson said. “What we didn’t quite understand is that soils have inherent soil properties that we can’t change but the problem comes in the soil’s dynamic soil properties that can be changed through management but have been taught as properties based on soil type.”
Research came slowly but surely diagnosing the problems with long-term tillage and its effects on soil health and productivity. Assessing the sources of aggregate stability and soil structures that lent themselves to water infiltration gave scientists clues along the way.
“In the late ‘90s some researchers started discovering substances in the soil that were given off biology in the soil that acted like glue,” Peterson said. “They glued individual particles of sand, silt and clay together in the soil.”
Aggregate stability can either be built or destroyed in three to four years, Peterson said. Soil structure can be greatly improved quickly by acknowledging and managing for the two sources of aggregate stability: biotic glues and exudates.
Biotic Glues and Exudates
The easiest method to visualize biotic glues is to imagine the slimy trail an earthworm leaves behind. Earthworm burrows don’t collapse behind the worm digging them, and the secretions from the worm’s body help stabilize pores in the soil to enhance water infiltration and holding capacity.
Earthworms are not the only critter extending these benefits in the soil. Many kinds of fungi, good nematodes and even pill bugs can release secretions that stabilize soil structures.
“Mycorrhizal fungi gives off this secretion into the soil that begins the gluing process,” Peterson said. “It begins the process of sticking one piece of sand, silt or clay to another.”
The more soil organisms thriving amongst the soil structure, the more the soil is bound together in the presence of water, Peterson said. However, cultivation can greatly decrease soil organisms as well as tear through the structures they have in place. Plant roots give off similarly bonding secretions through called exudates, which not only bind the soil but also draw in more soil biology.
“Plants give off exudates or secretions through their roots,” Peterson said. “They give off as much as 50 percent of the energy they derive from sunshine, minerals and water by oozing it out through their roots to attract organisms in the soil to bring them nutrients.”
Exudates can be a wide variety of things from sugars and proteins to amino acids, Peterson said. The relationship between the plant and the microorganisms they draw in is mutually beneficial in that the plant gives up some of its nutrient knowing it will receive many more in return.
“The fact is the majority of nutrients and moisture goes into a plant through a microorganism, not directly through root interception,” Peterson said. “The biology brings it to the area around the root because the plant is giving off exudates.”
Biology lives in pore space between aggregates, the same place the water flows, Peterson said. For the organisms living in the soil, it’s often considered to be an aquatic ecosystem.
“Soil biology swims in the film of water on the aggregate’s surface,” Peterson said. “That’s why water is the driver of the whole system.”