Under its new operator—who made multiple lime applications and vertical tillage passes to remove dense layers before converting the field back to no-till—Farm B is producing higher yields, although it hasn’t yet caught up to Farm A. In addition, soil organic matter content—one measurement of soil health—is trending upward. More organic matter correlates to increased nutrient cycling and water availability, Ferrie explains. “Each percent of organic matter means 20,000 more gallons of water per acre stored in the soil,” he says.
Ferrie believes Farm A’s soil organic matter has reached an equilibrium level, in which the soil is burning as much carbon as it produces. “Only a certain amount of carbon can be sequestered and maintained in any soil, based on its management and climate,” he says. “The soil in the cemetery also is in equilibrium. The cemetery soil’s organic matter content is probably about equal to that of native prairie. In the adjacent farm fields, cropping practices had caused organic matter content to decline until the soil reached a new equilibrium level.” The graph suggests improved soil health practices on Farm B began having an impact in only two years, when organic matter readings began moving upward in 2012. It also suggests the soil might have begun moving to a new equilibrium level about 2015. Time will tell about that. The equilibrium concept suggests it’s unlikely the red soils of the South, which contain less carbon, will never be black with organic matter like the soils of the northern Corn Belt, even if kept in permanent pasture. But the Farm A/Farm B comparison shows improved soil health practices can raise organic matter/carbon content to a new equilibrium level. In future years, the addition of cover crops on both farms will reveal whether adding that soil health practice can push the equilibrium level upward. Ferrie’s soil health study also has yielded knowledge you can use to evaluate soil health changes on your own farm. Early on, his efforts produced more frustration than enlightenment. “The problem was that many soil health scores, as reflected in various tests, go up and down based on seasonal environmental conditions,” he explains. For example, he says, “in a cover crop strip trial, the cover-cropped soil consistently tested higher than the non-cover-cropped soil in biological activity. But one year, the numerical scores for both treatments would be in the low range and the next year they would be in the optimum range. A year later, the cover-cropped soil again tested higher in biological activity, but the test’s numerical scoring system placed both soils in the optimum range.” “To be useful, soil health test results must be repeatable in the same year and from one year to the next. Eventually we realized weather and other environmental factors were moving the numbers around.” Ferrie is confident soil health is improving with cover crops and reduced tillage. It’s not the numerical score, but the relationship between new and old practices that matters when realizing the benefits. Based on that realization, Ferrie now uses the farms’ normal practices as an “anchor point” and compares the difference between the new practice and the anchor point to determine the effect. In the cover crop study, covers were having a beneficial impact if the difference in soil health between cover and non-cover (the anchor point) areas increased over time, regardless of the numerical score. “A number of soil health tests can be used in this way,” Ferrie says. “The anchor point can be an undisturbed fencerow or a pasture, or it can be an area where you continue to use the same management practices [without changing them because any change, such as a new tillage system, could start moving the soil to new equilibrium levels]. In the soil rehabilitation study, Farm A’s soils serve as the anchor point.” Eventually, the study will reveal if and how fast the soil health gap bet-ween the two farms can be closed.
Understanding Organic MatterAll carbon, which makes up most of what we call organic matter, is not created equal, and that can make soil test readings confusing. Active carbon/organic matter is metabolized in a few months to a few years. Slow organic matter requires decades, and passive organic matter requires hundreds or even thousands of years. “Most nutrient cycling involves active carbon,” says Farm Journal Field Agronomist Ken Ferrie. “The active portion, which makes up 10% to 20% of the organic matter in soil, quickly increases and decreases based on the management system and the climate. “That’s why looking at just one or two years of soil test readings might provide an inaccurate picture of what’s happening in soil. Organic matter readings might vary by a one tenth of a point, or even more, just because of the volume of crop residue and weather conditions. Readings might even vary from month to month because the active organic matter cycles so rapidly.” To see what really is happening with organic matter in your soil, look at multiple years of soil tests (the more, the better), Ferrie advises.
Tests to Measure Soil HealthHere’s a list of soil health tests Farm Journal Field Agronomist Ken Ferrie uses to measure the impact of improved management practices on soil health. Because the numerical ratings produced by the tests are influenced by cropping system and environmental conditions, the soil being tested should be compared to an anchor point. “The relationship between the two areas will show whether new practices are improving soil health,” he says.
Chemical TestsStandard Fertility Test:
- Organic Matter
- Nitrate Nitrogen
- P1 Phosphorus
- P2 Phosphorus
- Cation Exchange Capacity
- Percent Base Saturation
Biological TestsWater-Soluble Extract—Haney Test:
- Nitrate Nitrogen
- Ammoniacal Nitrogen
- Total Nitrogen