Despite heavy spring rains, crop residue on Farm A remained in place, even on the slopes, thanks to the healthy soil structure. Even with less slope on Farm B, the unhealthy soil gave way to washing and erosion.
On-farm tests help restore healthy soil characteristics
Imagine two farms less than a mile apart with the same silty clay loam and silt loam soil composition. During the past three years, corn yields on Farm A have averaged 200 bu. per acre on the silty clay loam soil and 187 bu. per acre on the silt loam. Farm B, on the other hand, has averaged only 130 bu. per acre on its silty clay loam portion and 123 bu. per acre on its silt loam.
The farmers of the two tracts use similar practices—no-till and a mostly corn/soybean rotation. The primary difference is that Farm A has been no-tilled for 30 years, and Farm B for only two years. Prior to that, it was farmed using horizontal tillage.
The massive structure of Farm B’s unhealthy soil shows why water fails to infiltrate and crop roots don’t penetrate.
Leaves, husks and silks were still evident on Farm B two years after a corn crop. Their presence indicates an absence of soil organisms, which indicates poor soil.
Perhaps you’ve seen similar yield differences in your own fields and wondered why one area yields more corn than another. Modern testing tools can help you pinpoint the culprit. On Farm B, the lower yields can be linked to poor soil health.
Farm A and Farm B are real. Farm Journal Field Agronomist Ken Ferrie has been working with Farm B for four years, helping the farmer restore soil health in order to boost yields.
In the beginning, Ferrie used soil pits and visual observation to evaluate soil health. But now, simple on-farm tests let him and any farm operator give the soil a "physical exam." The tests provide numerical soil health ratings, which serve as benchmarks for evaluating soil health improvements.
Ferrie gave both farms a physical exam this past spring. "Because of the difference in soil health, the best soil on Farm B still can’t yield as well as the poorest soil on Farm A," he says.
"Improving soil health means sustaining productivity and profitability," Ferrie explains. "It requires a systems approach because healthy soil involves many components. The components fall into three categories—physical, chemical and biological.
"In some cases, it might be possible to fix physical and chemical problems fairly quickly. Often, improvements take many years, especially when the biological component is involved. Even so, the 70-bu. yield difference between the two farms shows that improving soil health is worth the effort."
A physical exam—just like the one your doctor gives you—begins by assessing the farm’s appearance. Even after four years of effort on Farm B, the visual differences were still striking.
"In spring 2012, despite some heavy rains, all of the old crop residue remained in place on Farm A, which even has some slopes." Ferrie describes. "On Farm B, with much less slope, the old crop residue and the soil eroded away, carried off by water."
A glance at the soil surface revealed part of the reason why water is infiltrating into the soil on Farm A but running off the surface on Farm B. There were thousands of night crawler burrows visible beneath the residue on Farm A but almost none on Farm B. "Among the benefits of night crawlers, their burrows allow water to infiltrate the soil," Ferrie says. "They also help remove excess water, functioning like part of your drainage system."
Part of the reason water couldn’t infiltrate the soil of Farm B was its degraded structure. Digging revealed impenetrable blocks of soil, compared with Farm A’s healthy crumb-like soil structure containing macropores for water and air.
Another symptom of poor health, visible on the surface of Farm B, was two years’ worth of old crop residue. Not only was 2012’s soybean residue present, but even the fine leaves, husks and silks, which should be among the first and easiest to decompose, were present from a corn crop grown two years ago.
"That indicates a biological problem because residue is decomposed by soil organisms," Ferrie says. "The absence of night crawlers is one of the indicators that confirms it."
Simple tests conducted by Ferrie’s assistant, Thomas Zerebny, placed the degree of Farm B’s problems on a numerical scale. He used equipment from a Gempler’s Soil Test Kit.
A slake test, which involves immersing surface soil in water and seeing whether it holds its structure, produced scores of 2.7 for Farm B’s silt loam and 5.0 for its silty clay loam, compared to 3.7 and 5.7, respectively, for the same two soils on Farm A. The higher the score, the healthier the soil structure and the less chance it will seal over during a rainstorm and restrict infiltration.
Zerebny used a rainfall simulator, available from Cornell University’s Soil Health website, to analyze aggregate stability or structure in the top 6" of soil. It revealed that structural problems on Farm B are not limited to the surface of the soil.
The rainfall simulator also documented the difference in water infiltration caused by poor soil structure. Farm A’s silty clay loam took in 8.6" of water per hour, compared with 2.8" per hour for Farm B’s silty clay loam. Farm A’s silt loam soil took in 3.6" of water per hour, compared with only ½" per hour on Farm B’s silt loam.
Gas detection tubes (also called Draeger tubes) were used to measure the amount of carbon dioxide being released by soil organisms. The beneficial organisms breathe oxygen and release carbon dioxide, just like people, which is why soil needs pore spaces—to provide oxygen for the microbes. The amount of carbon dioxide is an indication of microbial activity. The results showed about 50% more microbial activity in the healthy soils of Farm A.
Health quest. Ferrie’s examination of the results showed that the operator of Farm B needs to continue to focus on physical and chemical issues to improve soil health. The operator is using vertical tillage tools to remove hardpans, compaction and tillage layers.
Vertical tillage and liming work together to fix structural problems. "When a field gets extremely acid, acidity destroys structure and stops water infiltration," Ferrie says. "When we apply lime, we are attempting to flush out the acidity. If we have poor infiltration, we can’t get water into the soil to make the lime work.
"Applying lime, (calcium carbonate) helps fix structural problems and keeps pH in the 6.3 to 6.5 range, which is optimal for soil microbial activity. The carbonate bonds with hydrogen (acidity) and helps flush it out of the soil."
Calcium improves structure by helping to flocculate clay particles. Flocculation means the particles are held together, yet somewhat apart. "It’s the first step in creating better aggregate stability or structure," Ferrie says. "A healthy crumb-like structure lets water infiltrate and contains macropores. The macropores hold air and usable water, which is accessible to crop roots.
"Together, vertical tillage and lime applications will let us gradually build up soil pH from the 5.0 range, where it was when the operator took over the farm," Ferrie says. "Eventually, after soil health improves, he will no-till Farm B just like his other farms."
Cover crops are also part of Farm B’s recovery plan. Deep rooting crops can penetrate some hardpans and compacted layers. The roots of grass crops aid in the process of producing a glue-like substance that helps bind soil particles together.
In fall 2012, the farmer’s initial attempt to aerial seed a cover crop of annual ryegrass and tillage radishes failed, apparently because of environmental conditions. That illustrates how resuscitating abused soil takes a long time—probably decades for Farm B.
Regardless, gradual improvements in soil health will lead to gradual improvements in yield, Ferrie concludes. They will also lead to healthier water sources because of fewer nutrients washing away and a more sustainable farm for future generations.
Building on the Systems Approach, the Soil Health series will detail the chemical, physical and biological components of soil and how to give your crop a fighting chance. www.FarmJournal.com/soil_health
You can e-mail Darrell Smith at firstname.lastname@example.org.
- October 2013