by Harold Schrock
I was privileged to have received a copy of a university level study recently completed by Claire LaCanne and Jon Lundgren. This study, “Regenerative agriculture: merging farming and natural resource conservation profitably”, is now in the peer review process and lends some scientific documentation to observations that have been widely observed and discussed among my regenerative farming friends. This published paper documents several interesting observations, such as the organic matter accumulation characteristic of regenerative agriculture and the absence of insect pests in spite of no insecticide applications; but what I want to focus on in this article is the documented direct correlation between particulate organic matter concentrations and field/farm profitability.
Particulate organic matter, as I understand it from their references, refers to the portion of organic matter that is biologically alive and cycling relatively rapidly between plants and soil. This is separate from the total organic matter in any given soil. Although more organic matter is typically better than less, organic matter by itself does not equate to soil health. Total organic matter correlates fairly well with the soil’s water holding capacity and nutrient holding capacity, but does not directly correlate with a soil’s ability to feed plants. The particulate organic matter does directly correspond with soil’s ability to host healthy plant production. The laboratory test to document these levels is not available at most agricultural laboratories but I doubt if that is a practical concern, because these soil conditions are fairly easy to observe in the field and the path to achieve higher levels is well understood.
Soil aggregation is the visible indicator of higher levels of particulate organic matter. It’s easy to observe the crumb structure of a soil and it is also easy to do a slake test, (place a clump of soil in a transparent container of water and watch how long it takes to dissolve; the longer time it takes to turn into sludge in the bottom of the container, typically the better the soil aggregation). The real question is, what is the value of this soil aggregation and how do we achieve more of it?
The value of soil aggregation and particulate organic matter can hardly be over estimated. Soil gas exchange is one of the most important functions of soil and is largely dependent on soil aggregation. Contrary to the expectations of many farmers, nitrogen is not the number one plant nutrient needed. By a huge margin, the number one plant nutrient needed by volume is carbon. The great majority of the carbon used by plants in their growth comes from atmospheric CO2 (carbon dioxide). While atmospheric CO2 levels have been increasing in recent history and are now high enough to cause concern in some scientific communities, the concentration in the atmosphere at large is not nearly high enough to maximize plant growth. The CO2 concentration in the first couple of feet above healthy soil can be 10 times or more normal atmospheric levels. CO2 level variation is the primary reason we can often observe a growth response immediately following row cultivation. It is also a good portion of the growth response observed from a soil nitrogen application. Nitrogen interacts with soil carbon, releasing higher levels of carbon dioxide and causing additional plant growth. This is one reason why side-dress nitrogen is typically much more efficient than pre-plant applications.
So how do we achieve higher levels of soil aggregation and particulate matter? There are some chemical interactions that have a small effect. Perhaps the strongest of these is the calcium/magnesium balance. Calcium tends to flocculate clays, spreading the layers for a looser chemical bond. Magnesium has the opposite chemical action, relaxing chemical soil structure and causing a tightening effect. These chemical effects in soil are real but they pale in significance compared to biological construction. By far the greater portion of healthy soil aggregation comes from the biological life within the system.
Achieving healthy biology in the soil starts with drainage; aggregation is responsible for most of good soil drainage but aggregate-building biology functions very poorly or not at all in saturated conditions. If the field has a naturally high water table, tile and/or ditch drainage is the only way forward. If this is not done it is nearly impossible to achieve profitability with high-value crops. Fields that are impossible to drain are likely best utilized for Reeds Canary or similar perennial bedding/biomass production. Some soils are waterlogged because they are tight but do not have a high water table. These can often be worked with from the top down, feeding the biology and strategically ripping to overcome compaction issues.
Minerals, whether naturally occurring or provided by fertilizer, are an important part of building soil biology. Both plants and biological life are very dependent on sufficient quantities of mineral nutrition in the soil profile. This is well known and understood but sometimes the fact is missed that any mineral essential for plant production can be a limiting factor in the overall system. Ordinary soil tests certainly have value but they do a very poor job at measuring metallic element availability for plant growth. If our soils are less than optimally healthy, measuring nutrient levels in the crops themselves is very important for understanding weak links. A forage test including wet chemistry micronutrient analysis is of at least equal value to soil tests for understanding where fertilizer dollars are best spent. Foliar feeding, based on forage analysis, is often the most cost effective way to supply needed plant nutrients for optimal sugar production.
Sugar production is easily the most important factor of all in building biological aggregation. Sugar is the food for microbes that produce glomalin and other glue-like substances that bind the particles together. Microbes also mine soil minerals to complete their diet requirements, creating additional plant-available minerals. Excessive tillage, as well as some herbicide and fertilizer formulations, are known to disrupt soil biology and aggregation, but most soil destruction happening all across North America today is a direct result of low sugar production. This is either from lack of plants or from lack of plant health and photosynthesis production. We get the first situation in the case of summer cropping with no corresponding winter cover/cash crop. A healthy corn crop in the height of the growing season will push as much as 70% of its sugar production into the soil in the form of root exudates. This can be a very significant amount of sugar, as much as 8-9000 pounds per acre, but is in itself not enough to keep robust biology functional all year around. Biological feast and famine will not build stable soil structures.
Great sugar production is equally dependent on the health of the crops growing. Plants struggling from environmental stress such as flooding or drought will not produce significant levels of root exudates. Neither will plants limited by mineral nutrition needs.
To summarize: Keeping the soil covered as much as possible with green growing plants and fertilizing for optimal photosynthesis and sugar production are the primary keys for building soil aggregation. Interestingly, these same two factors are primary keys to farm profitability on multiple fronts. Producing more and better quality crops not only improves cash flow; it should ultimately also produce healthier soil and reduce input requirements, leading to higher profits.