Soil Health - 2

Is Your Soil Breathing?

While many assume carbon is simply coming from air, the role that healthy soil respiration plays in sustaining plants is often overlooked. (DTN photo by Pamela Smith)

I am a soil health fan. I like learning more about it and discovering ways to improve it on our family farm. The challenge is measuring progress and being able to measure it myself without breaking the bank.

In the first part of this series of articles I encouraged growers to think of the soil as an engine. The productivity (horsepower) of that engine can be improved, but first we need to measure the existing horsepower. The Solvita test is an affordable tool growers can use to estimate the size of soil's engine by measuring respiration or carbon dioxide (CO2) release.

Most of us think we are doing what is good for crops. "The normal practice is to provide crops with nitrogen, phosphorus and potassium," said Will Brinton, the environmental scientist who developed the Solvita test and founded Woods End Soil Lab, which distributes the test. "We take it for granted that our crops will get the CO2 they need from the surrounding air. But things have changed over the years. Soils have fallen so low in organic carbon that they no longer produce enough CO2 to feed vigorously growing plants."

Brinton said active soil can release a lot of CO2 and it can be measured. "Today the atmosphere contains about 400 ppm (parts per million), crop canopy about 800 ppm, the layer of litter on the soil surface has about 1500 ppm and the soil as much as 4000 ppm CO2," he said.

Very healthy soils will have CO2 bursts of 150 ppm or more. Keep in mind that microbes feed on carbon, respire CO2 and recycle nutrients to feed roots and humic compounds to improve the soil structure. The bigger the burst, the bigger the engine.

TWO TESTS

There are two Solvita tests. The Solvita Basal Respiration Test is used on-farm and can be done at home. The Solvita Soil CO2-Burst Test is run in a commercial laboratory that does soil analysis under more precise conditions. With both methods, the user purchases specially designed paddles that collect CO2 and a meter that will read the paddles. With the basal test, users have the option of reading color change off a color chart.

While the basal test measures CO2 release under natural field conditions on any given day, the burst test measures the potential of that soil to release carbon dioxide. "The CO2-Burst test works because when you dry and rewet the soil, it will give off a burst of carbon dioxide. This burst is an indicator of (potential) biological activity," Britton said.

With the CO2-Burst test, the soil is dried and ground like a conventional soil sample in a laboratory. The rewetting procedure is standardized with a special soil-capillary moistening beaker to conveniently add the correct amount of water for the test without over-wetting the soil.

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"No one test will evaluate all the components of soil health, as it is tedious," said Brinton. "However, the CO2-Burst is a good indicator. It integrates everything related to soil quality and health and can monitor incremental improvements in soil from better management.

"Yields are stagnating for many growers globally, because of climate change, salinization, erosion, pests and diseases and depletion of biology and soil fertility. Soil fertility is not just about applying more fertilizer," he added. "Soil biology is an important component. Unfortunately, growers don't see that they are depleting their soil's biology."

COLLECTED SAMPLES

In 2013, I collected samples and sent them to a laboratory to run the Solvita CO2-Burst Test. I wanted to understand the technology and investigate its potential.

From that experience, I was both intrigued by what I learned and disappointed. The results were low -- although in reality, they were probably average for a typical corn and soybean rotation, as these soils do not typically respire a lot of CO2.

Last spring (2014), I acquired the equipment to run the basal test. I also ran the burst test in a commercial laboratory to compare both sets of numbers. Over the summer, I also ran a number of soil samples at different times through the season.

For the basal test, I weighed 100 grams of moist field soil collected from a routine soil samples with cores 6 to 8 inches deep. The ideal soil sample is the same as for sampling soils, not too wet or too dry. The sample is placed in a small plastic container with a CO2 paddle, and the container is capped with a lid and incubated for 24 hours at room temperature. After the 24-hour period, the paddle is placed in a meter. The meter will scan the color change of the paddle and provide a reading in ppm CO2 or pounds CO2 per acre. The basal test gives a measurement of undisturbed soil right from the field. Temperature and moisture levels can affect respiration levels. The basal test allows a grower to test a soil's respiration on his own farm.

BASAL LOWER THAN BURST NUMBERS

By comparing the two tests, I learned that basal numbers tracked burst numbers up and down across fields with different history and landscapes. However, the basal numbers were always 10% to 20% lower than the burst numbers. I attribute this difference to the fact that the burst method is a measure of potential respiration under ideal moisture and temperature conditions and the basal test is the actual value under less-than-ideal field conditions. I evaluated poor and healthy soils under corn and soybeans, pasture, CRP grass, and fallow stubble after winter cereals and soils under an eight-way cover crop after winter cereals.

Brinton informed me that a very healthy forest soil with a lot of litter and nutrient recycling can produce more than 150 ppm of CO2 in 24 hours. A CO2 reading of 0 to 20 ppm is very low; 20 to 60 ppm is moderate; and 100 to 175 ppm is very high. My results based on the burst test are as follows:

-- 12 to 15 ppm in fallow soil a few weeks after barley harvest; -- 30 to 40 ppm for an unhealthy soil in a corn and soybean rotation;

-- 40 to 50 ppm for a soil in a CRP grass;

-- 50 to 60 ppm for an average soil in a corn and soybean rotation;

-- 80 to 90 ppm for a healthy soil in a corn and soybean rotation;

-- 85 to 95 ppm or a soil under a six-way cover crop two months after rye harvest.

I've decided to look at my soils as the little engine that can. The next big jump in yield just may come from improving soil productivity while reducing fertilizer inputs. The Solvita test is a way to measure it.

In the next installment I will share the tools I used to evaluate why the Solvita results might have differed and what that means to soil health.

Dan Davidson can be reached at AskDrDan@dtn.com

Follow Dan Davidson on Twitter @dandavidsondtn

(PS/ES/CZ)

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