BY LAUREN KRIZANSKY
Manipulation. The word stirs up images of clever characters or bodies twisted on a chiropractor’s table, not of farmers examining the soil. This art of deliberate control, however, is becoming deeply connected to agriculture, and the practice is giving farmers a fresh relationship with the carbon cycle.
Agriculture removes large amounts of carbon from the cycle in the form of food. Replenishing the carbon in this part of the cycle is possible, but modern crop production methods have stifled the flow. Linear carbon management in the fields has tipped the scales, taking the carbon exchanges out of balance. The quest for high yields with synthetic inputs has made agriculture the villain it ought not be.
“An amount of carbon always comes into the soil, and an amount always leaves the soil,” said Joel Williams, an independent plant and soil health educator working internationally to improve food and farm systems. “The question is how can we manipulate micro-organisms, how can we manipulate our management with each pass of that loop to capture a little bit and keep it in the soil and release the rest that feeds into the cycle?”
On farms and ranches, carbon is primarily lost through mismanaged tillage, erosion, burning, overgrazing and frequent low-carbon crops. These same tools are also critical to balance out the carbon cycle. When carbon becomes the cash crop and a living system becomes the priority, agriculture can manipulate the cycle for the better.
“In order to sequester, you have to strengthen the cycle,” Williams said. “There is nothing wrong with releasing carbon from soils. That is completely normal. That is what helps plants breath. It is to the extent that we have done this that it has become out of balance.”
In agricultural systems, carbon plays four parts. Retired North Dakota-based USDA-NRCS Soil Health Specialist Jay Fuhrer explained how the element moves through a corn crop. It begins, he said, with the harvest and the third of the crop’s carbon that is found in the grain.
“We usually put tires under this part,” Fuhrer said. “Exporting 100 percent of this portion for people food, energy or livestock feed.”
The second part considers that one third of the crop’s carbon is in the residue, of which upwards of 85 percent is oxidized into the atmosphere. The remaining third of the crop’s carbon is in the root mass, where about 70 percent is no longer available to the agricultural cycle.
The fourth part of carbon’s role in agriculture is found in the root exudates of a young, growing, green plant, he said. The soil food web consumes this resource for energy to complete its tasks, especially during the first one to two months of growth.
“The microorganisms are carbon hungry,” Williams confirmed. “We need to bring carbon into soils to feed microorganisms to drive nutrient cycling, which then drives production. We need those microorganisms to be releasing that carbon, to be respiring.”
This is what the farmer can do to support the efficiency, the health and the connectivity of the carbon cycle. Agriculture can feed not just the people, but the life that begets human life. It can look beyond just transferring atmospheric carbon dioxide into long-lived pools.
Under Cover Carbon
Contrary to their reputation, fallow lands do not restore fertility in a crop rotation. When a farmer decides to remove plants from the field, he or she also chooses to have a counterproductive interaction with the carbon cycle.
“One is maintaining the carbon cycle when we have living cover,” Williams said. “You are maintaining that flow. When you have a fallow period, you are not. Typically, you are going to be losing carbon.”
Fallow lands result in chemical oxidizing, he explained, because the sun is cooking the ground.
“Fallow is turning it off,” Williams said. “Cover crops are engaging with the carbon cycle through photosynthesis.”
Cover crops contribute to the carbon cycle through a diverse network of specialized personnel underground. They fill the carbon gap that fallow lands and commodity crops leave behind.
“When we use cover crops we are feeding the soil system for a greater time throughout the year, and we start a soil-building process through biology,” said Lance Gunderson, president and co-owner of ReGen Ag Labs in Pleasanton, Nebraska. “Remember that soil without biology is called dirt, and that is geology. When we do fallow, we are creating dirt, because we are not supporting the biology that supports our crops.”
Gunderson believes that fallow fields are more detrimental to soil than tillage, but it is a combination of the two practices that creates serious problems.
“Yes, we should reduce tillage when possible, but I have seen far too many long-term, twenty-plus year, no-till fields exhibit many of the same symptoms of a poor soil as those seen in conventional systems,” he said. “It all boils down to a lack of carbon and diversity.”
Bringing carbon into a cropping system through cover crops entices the carbon cycle to sustain the microbial life under the ground that performs many tasks that improve the soil’s health. This manipulation of carbon also contributes to the cash crop that will find its way into the cover cropped fields in coming seasons.
“Carbon is the backbone for providing structure to the soil,” Gunderson stressed. “Plants exude a relatively large portion of their photosynthate carbon into the soil through the roots. These root exudates help aggregate the soil both directly and indirectly as food for microbes.”
The simple compounds are then used as a food source, he said. The well-fed microbes are then able to produce many secondary compounds that act as a glue to hold soil particles together.
“I like to think of it as the mortar that helps hold together the bricks of our homes and businesses,” Gunderson said. “The microbes are building and altering their habitat through the use of carbon.”
The stronger and more available the underground habitat, the more productive the microbiology are, for example, in building immunity. Williams said soils rich in carbon, or, more specifically, soil organic matter, are consistently found to possess mechanisms of pathogen suppression.
“There is a highly specific interaction between a couple of organisms between the pathogen and some other beneficial microbes, bacteria or fungi that attack the disease,” Williams explained. “There are many unknowns, which is why we maximize diversity in the hopes that some of those antagonistic species will be present.”
Fuhrer added, “It really is about food and a home. By providing a diversity of plants, we help maintain and encourage the diversity of microbes and the balance. Allowing the microbe community to self-regulate, which our cropping and grazing systems benefit from by reduced disease impacts.”
When Cycles Collide
Carbon is at the center of the water cycle.
Although soil texture plays a role in water dynamics, Gunderson explained that the amount of carbon within a certain textural class also has a profound effect. Increasing soil carbon increases soil aggregation, which increases infiltration. Increases in carbon also reduce bulk density or increase the pore space between aggregates to allow for greater water holding capacity.
“Carbon itself can act as a sponge to increase water holding capacity as well,” Gunderson said. “Some people might be thinking that they have too much water or that their soils are too wet, so why increase carbon? Increasing soil structure allows for better drainage throughout the root zone, but it also helps with better gas exchange at the surface, which can moderate soil moisture in wetter environments.”
Increasing the functions of the water cycle means being able to capture every drop, hold that water and allow roots to explore the entire soil profile, he added. All of these lead to better water use efficiency and help increase photosynthetic capacity.
When considering carbon in the form of soil organic matter, there is an opportunity for the system to hold onto moisture and possibly to help the plant access water, Williams said. Water will infiltrate and photosynthesis will take place.
Amplifying the Cycle
Livestock is yet another tool to manipulate carbon.
“The act of grazing itself, if managed properly, can stimulate plants to produce greater root mass and increase root exudation to increase soil carbon,” Gunderson said. “Grazing also helps reduce many of the higher carbon or more lignified plants into readily accessible forms to speed up nutrient and carbon cycling by secondary consumers such as macroinvertebrates and microbes.” Grazing also removes very few nutrients compared to haying or silage operations, and the additional manure and urine help support soil habitat while recycling the nutrients back to the land. It increases root exudation and increases feeding microbes and nutrient cycling so the pasture can recover and regrow.
“Plants which are grazed respond differently,” Williams added. “They can boost their photosynthetic capacity.”
The grazed material is put through digestion of the animal’s rumen and spit out in its manure. The rumen does the work, making more nutrients available to the microorganisms in the soil.
“They are more palatable to the microorganisms,” Williams said. “They can digest it easier. Wherever animals are included in cropping systems [and] farming systems, that soil organic matter increases.”
Fuhrer added, “Our soils evolved with a diversity of plants, animals and microbes. Consequently, we need a diversity of livestock on our landscapes.”
When hooves on the ground isn’t an option, compost or manure spreading is often used to fill this need. Control of this input is critical, too.
“Manipulation,” echoed Mark Inness, a veteran composter in southern Colorado “[is] the difference between good compost and manure.”
His belief in maturity time and pile turns result in balanced proportions of carbon for energy and nitrogen for protein production. If the C:N ratio is too high, excess carbon decomposition slows down. If the C:N ratio is too low excess nitrogen, the compost pile will have management challenges.
Compost manipulation also influences the amount of moisture present and conductivity. Moisture affects handling and transport. A desirable moisture content ranges between 40 and 50 percent. Conductivity or soluble salts measures the conductance of electrical current in a liquid-compost slurry. Excessive soluble salt content in a compost can hinder seed germination and proper root growth.
Land managers have a choice for how they manipulate the carbon cycle. In addition to the actual tools available to make practical changes, there are also resources to champion a greater shift to carbon-conscious agriculture
“As a society, we ask a lot from our farmers and ranchers, often with very little thanks or appreciation,” Gunderson said. “I don’t think that we should expect them to do this alone. We need the right support groups and organizations in place to help and support them in making this a reality. I believe, however, that agriculture could have a greater positive impact on the carbon cycle as a whole than nearly any other industry.”
Lauren Krizansky is an agricultural journeywoman. She loves, lives and works with her partner, Brendon Rockey, on Rockey Farms in Center, Colorado.