Talking about soil carbon is all the rage these days, but what does this have to do with productive and sustainable agriculture?
The answer is: a whole lot.
Soil organic carbon (SOC)—the black and broken-down component of soil organic matter (SOM)—is the structural basis for healthy soil, and also the key to long-term soil fertility. Richer soils have more carbon, and over-exploited or arid soils are carbon-depleted.
In earlier forms of cultivation, organic matter was the only fertilizer available: whether that was compost, manure, or even human night soil. These ancestral agricultural practices gave carbon—broken-down organic matter—back to the soil while delivering nitrogen (N), phosphorus (P), and potassium (K) as well.
With the advent of chemically-synthesized fertilizers, however, using only solid organic matter fertilizers has fallen by the wayside in favor of more efficient chemical formulations, except among the most die-hard organic farmers. Indeed, chemically-synthesized fertilizers are more predictable and contain higher concentrations of nutrients.
Though valid, these concerns should not deter one from integrating applications of organic matter into the fertilization schedule, if only to invest in long-term soil quality and to save on conventional fertilizers.
Carbon, for example, helps in storing bioavailable nitrogen for much longer periods of time, and carbon that is sequestered in the soil does not volatilize to the atmosphere. Soil with more organic matter also holds more water, is easier on tilling and planting equipment, and resists compaction.
Compost—broadly defined—is an ideal source of soil organic matter. There are some caveats, though: spreading immature compost carries the risk of using up soil nitrogen, as the decomposition of organic matter utilizes nitrogen. Furthermore, immature compost can create anaerobic pockets or films that host plant-harming bacteria or contain toxic substances.
Manure, on the other hand, is often a more readily-available source of organic matter, but has a higher potential for carrying human and plant pathogens, as well as weed seeds if it is not composted to some extent.
Both options, however can benefit the soil in ways beyond adding soil carbon: they can increase the biological diversity in the soil itself, and chelated micronutrients. The key to using them effectively is using them when they are mature and safe to use in the field.
With precise planning, application, and management with SMART! Fertilizer Management software, organic matter fertilizer can be used in conjunction with chemically-synthesized inputs in order to both return carbon to the soil and maximize productivity and yields.
To maintain organic matter in the soil after each application, there are a few practical steps to take: reducing tillage, and controlling erosion are among them, as are practices like cover cropping and leaving crop residue on the field to decompose.
To conclude, stewardship of soil carbon is one of the best investments in healthy soils and crops—and a healthier environment—for decades to come.