The Halderman Companies know firsthand how important maintaining and improving soil fertility is to the value of your farmland investment.  An important aspect of soil fertility, i.e., the ability of the soil to support plant growth, is the organic matter content of a soil.  Looking strictly at plant nutrition, it may not seem to be of critical importance, since plants can only take in the nutrients needed in an inorganic form.  However, the indirect effects of organic matter in the soil are very significant.

Soil organic matter (OM) is expressed on soil test results as a percentage of the soil.   It is plant or animal tissue that is decomposed or is in the process of decomposing.  It includes living and dead microbial populations, plant residues in various stages of decomposition, and stable organic matter often referred to as humus.  For non-scientific purposes, organic matter can be thought of as synonymous with soil carbon.  Many of today’s Midwest farmland soils that were originally prairie had a natural level of 6-12% before regular cultivation.  Today 2-5% is common and 4-5% is a good target level for land in crop production since when OM is over 5% good drainage can be problematic.  Halderman’s goal is to implement farm management strategies to enhance and improve organic matter.

Organic matter is important to fertility for multiple reasons.  It is an important food source for microbial life.  The result of the microbial feeding is the conversion of nutrients into plant-available forms.  This is process called mineralization.  Most of the mineralization that occurs in our soils, and which naturally provides nutrients for plants, is dependent on microbial activity.  Organic matter also acts as a type of glue that stabilizes the soil aggregates and helps it avoid compaction and keep the soil environment capable of providing oxygen for root respiration and growth.   Another very important benefit of OM is the water-holding capacity it adds to soils.   Common estimates from university soil scientists are that for every 1% increase in organic matter in a soil, water-holding capacity is increased by 20,000-25,000 gallons per acre.  That would come close to an inch of rain (which equates to just over 27,000 gallons per acre) that we can hold in our soil to improve tolerance to drought stress.

Years of tillage are the most significant factor in loss of organic matter on our agricultural soils.  Farms that  saved soil tests from 20-30 years ago and  used conventional tillage  practices throughout that time may often see a drop in OM of 0.5 or more over that time frame. Tillage is often said to ‘burn’ organic matter by turning over the soil and exposing more of it to atmospheric oxygen and consequently oxidizing much more of the carbon than would otherwise occur.  This causes a loss of carbon into the atmosphere but also releases a flush of plant-available nutrients.  (Not to get too far off-topic on a tangent, but this is sometimes viewed in isolation as an ‘unsustainable’ production practice since it can continually reduce the OM and productivity of a soil at a slow, but discernable rate.)  Tillage also breaks down the natural soil structure and has a negative impact on the microbial populations which lowers OM.

Until a few decades ago, we depended primarily on tillage to combat weeds and had no realistic alternative.  Today, the availability of effective herbicides as a tool to combat weeds has had a big positive effect by making it possible to achieve excellent yields utilizing some form of significantly reduced tillage or even no-till farming systems.  Unfortunately, there are also some negative effects of herbicide and pesticide use on microbial soil life, so it’s not an unmitigated positive.  Nevertheless, on balance, herbicides are a positive factor for soil life by enabling significantly less tillage while continuing to increase crop production.

Are we just going to keep slowly using up our soil organic matter until we get to zero?  The good news is that we can build organic matter in our soil while still producing great crops.  In the past, this was thought to be nearly impossible or at least a very long-term project.  However, more current experience demonstrates that we can make a significant increase in organic matter in as little as 5-10 years with a combination of practices.

One of the most obvious ways to do it is to utilize animal manure where available.  This should be done judiciously, since manure can sometimes have a high salt content which can have deleterious effects on crops.  However, when tested and managed well, it can be a great source of both nutrients and OM.

Since manure is not available for most acres, the cover crop approach  can be a fit on many soils is simply to keep living plant roots in the soil for as much of the year as possible.  Plant roots (far more than the plant residue we see on the surface after harvest) contribute to soil organic matter when they decompose.  More importantly, while living the plant root excretes various starches and proteins called root exudates.  These exudates feed microbes in the soil.  This establishes a symbiotic relationship because while the plant root exudates feed microbial life, the microbes are mineralizing OM and some soil components to feed the plants.  This is a key benefit of cover crops.

Some crops are more beneficial for root growth that contribute to soil OM.  Of the common crops in the Midwest, grass species like corn and wheat are more beneficial due to larger root mass than soybeans.  Incorporating these management practices, i.e., manure use where possible, cover crops, crop choice that includes corn and wheat, and minimizing tillage, can result in building soil organic matter without decreasing current yield levels.

Halderman Farm Management seeks two outcomes on farms we manage.  First, we want to maximize the landowner’s current farm income by creating win-win leases with our farm operators and second, we want to increase the value of the farm long term.  This requires the use of sustainable farming practices and increasing soil fertility, including organic matter, over time.  Working together we can make sure our client’s farms perform the best they can for generations to come.