As spring arrives and the soil warms up, it comes to life and becomes very vibrant and begins to thrive. One of the by-products of this process is the release of nutrients tied up in plant residue and microbial and insect biomass. But the primary source of creating this thriving environment is the organic matter contributed by plant materials.
Soil contains organic matter, and it can typically range from 0.5 to maybe 6% of the total soil composition. But agricultural soils generally contain from 1 to 3%. It takes a long time to build organic matter but you can burn it off relatively rapidly will tillage or removal.
Organic matter feeds the soil. A range of soil animals and microorganisms feed on this residue, consuming carbon as energy and nutrients contained within. When these same organisms die they release important humic substances back into the soil and mineralize or release all the important nutrients that plants need.
Humic materials create the characteristic brown color of decaying plant debris and contribute to its brown or black color. These humic substances are important components of soil and benefit physical and chemical properties. In the soil, these compounds affect soil chemistry, nutrient cycling and bioavailability of nutrients. Humic substances come in three fractions: humic acid, fulvic acid and humin. Humic substances are chemically reactive in the soil yet recalcitrant, or resistant to further degradation.
During the mineralization process, organic materials are broken down by soil organisms. These organisms take up nutrients available in the plant residue or soil and are converted to organic forms within the cells of living organisms or to inorganic forms released to soil. When these organisms die and decay, this releases inorganic ions for plant or other microbe uptake. And the mineralization cycle begins all over again.
However mineralization can be stalled where there are not enough nutrients available to feed the pool of organisms. If a nutrient shortage is limiting microbial metabolism, nutrients liberated by mineralization or nutrients available from other soil will be taken up and retained by the microbial biomass. These same nutrients will be unavailable for plant uptake and are immobilized.
To prevent nutrient tie-up, it is important that soil contains a pool of nutrients that both meets the needs of the mineralization process as well as the needs of the crop until the mineralization process kick and recycling begins.