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Plants are truly amazing! They have the unique function of combining carbon from the air with moisture from to soil in the presence of sunlight and soil minerals to form carbohydrates. In spite of mankind’s sophisticated understanding of chemistry we still cannot produce sugar apart from plants such as sugar beets or sugar cane.
Carbon Dioxide (CO2)
An often-overlooked component in a plants ability to manufacture sugars is carbon dioxide (CO2). Inadequate carbon dioxide is many times THE limiting factor to higher yields. This necessitates a better understanding of how carbon cycles and how carbon dioxide gas is produced.
The goal in managing carbon is to build up the carbon reserves in soil in the form of humus and carbonates so that it is released as CO2 gas during the growing phase of the new crop. CO2 is released from the soil 24 hours a day but it is primarily taken up by the plant during the daytime. Since CO2 is heavier than air it accumulates during the nighttime.
The higher carbon dioxide accumulates during the night before dawn’s first light, the better the yield potential of the growing crop. Iowa crop advisor Mike McNeil maintains that CO2 release and amount of nighttime buildup is a quality indicator of soils. We fully agree. The production of high brix plants means a higher production of plant sugars, which are built from CO2, hence an even greater need for carbon dioxide. The greenhouse industry has known this for many years and regularly enhances the CO2 level in greenhouses to several thousand parts per million. This is 10 times the normal amount in air. The result: significant yield increase. This is the exact same thing we strive for in field conditions. We want to use the CO2 already in the air and enhance this with the CO2 released from the soil.
Older farmers will remember what happened when they cultivated young corn—it would grow six inches almost overnight after cultivation. Why? There are 2 reasons; soil conductivity was increased and CO2 release was speeded up. Combined these two factors caused tremendous crop growth.
I can imagine no-tillers and environmentalists cringing when I say that healthy soil should have increased levels of CO2 release. Yes we want it released so that it is subsequently reabsorbed by the growing plants. This results not only in increased yield, but also in increased volume of plant residue. If this plant residue is incorporated into the soil and digested by soil biology it causes the humus level in soils to rise. Increasing the humus level in soils is the truest form of carbon sequestration. Through the carbon cycle the CO2 that is released by the soil is returned back to the soil with interest i.e. even more carbons.
How To Start the Cycle of Increasing Carbon Storage in Soil
So how do we start the cycle of increasing carbon storage in soil? It is surprisingly simple; start using the premier “organic” fertilizer: limestone. That’s right—limestone, more specifically high calcium limestone. For years International Ag Labs has practiced low-level liming and seen great results. We have recommended annual applications from 200-500 lbs. of pelleted limestone be added to other fertilizers and broadcast together. We knew that regularly supplying calcium as a nutrient would greatly enhance crop growth—and we saw the results.
When Mr. McNeil presented the concept of using CO2 release as a quality parameter in monitoring soil health the lights went on and we made the connection. Limestone is calcium carbonate, CaCO3. Not only does it provide calcium, it also provides carbon. Did you know that a 500 lb. application of high calcium limestone provides 190 lbs. of calcium and 60 lbs. of carbon? When calcium carbonate is applied to soil it must be “digested” by soil biology before the calcium is made available for plant uptake and before the carbonate is released as CO2. This is the difficult part of biological agriculture. In contrast to conventional agriculture, which uses water-soluble nitrogen and potassium as the main growth elements, biological agriculture relies on making calcium available to the plant to provide the “growth energy.” Since calcium carbonate is not water-soluble it must be broken down by microbial action. Plant residues, another great source of carbons for the soil, also need microbial digestion to take it apart and store it as soil humus.
The Formazan Soil Test
For the last several years International Ag Labs has performed a soil test known as the Formazan test that answers the question “What is the digestive capacity of my soil?” This is a significant question that needs an answer when working with rock powders and plant residues used in organics and biological agriculture.
The Formazan test provides the biology in a soil sample with a specific amount of a food supply and waits a specific amount of time. We then measure the amount of metabolic enzymes given off by the bacterial and fungal species when they are active. The Formazan test is like the speedometer reading of microbial activity in the soil. It is an indirect microbial assay that gives us a picture of the forest—not the individual trees. Typical soils farmed with herbicides and pesticides will have a microbial activity level of less than 200 on the Formazan test. Biologically farmed soils that still use herbicides typically run from 300-500. International Ag Labs shoots for a Formazan reading of 600 as an entry-level good. At this level rock powders will be worked upon by soil biology and slowly made available. For organic soil we recommend a Formazan reading of 1,000 or greater since many nutrients in organic production must first be digested by soil biology. A Formazan reading greater than 2,000 represents a terrific soil with plenty of digestive capacity.
The Formazan test was developed by member of the Soil Science Society of America. Skujins*, who did a lot of original research on this test, found that the Formazan test directly corresponds to CO2 release, proteolytic activity, and nitrification potential. What this means in plain English is that low Formazan readings indicate a poor cycling of carbon, less microbial activity, and the inability of soil to break down organic inputs to supply plants with available nitrogen. This is very significant for organic farmers since all organic nitrogen fertilizers, with the exception of Chilean nitrate, require proteolytic activity and nitrification in order to make it available to plants. One last thing on the Formazan test, guess what the reagent or “food supply” is when incubating the Formazan test. CaCO3, that’s right—a fine grade of calcium carbonate. Surprise. Surprise.
The Soil Index
Some time ago International Ag Labs introduced a new parameter on our soil test called the Soil Index. The Soil Index is our attempt to answer the question: “What is the overall quality of this soil?” It is represented as a 0-100 score on the soil with the potential to show negative numbers if the soil is extremely hostile to growing plants such as when it has toxic salt levels. The Soil Index is simply the total of all points (positive or negative) from all the other measurements and ratios on the soil test. We have a desired level of 50 and greater, which we feel indicates the potential, but not certainty, of producing high brix. Readings in the 60’s and 70’s indicate a much better opportunity at achieving high brix and excellent yield.
In conclusion a healthy soil will have the following parameters:
- Good levels of CO2 release
- Good levels of humus
- Good levels of microbial activity
- Good levels of available calcium
- The potential to produce high brix
* Skujins, J. 1973. Dehydrogenase: An indicator of biological activities in arid soils. Bull. Ecol. Res. Comm. NFR 17:235-241