Soil organic matter consists of the remains of plants and animals in varying stages of decomposition. Organic matter can fall into one of three types: plant residues and living microbial biomass; active organic matter, otherwise known as detritus; or stable soil organic matter, otherwise known as humus. The living microbial biomass and detritus contribute to the fertility of the soil and the release of nutrients from decomposition. Humus is the end result of decomposition and is considered stable organic matter. This contributes to the structure, tillage, cation exchange capacity and dark color of the soil.
Benefits of maintaining high stable organic matter include physical benefits, such as reducing runoff, easier tillage and increased water holding capacity; chemical benefits, such as increased cation exchange capacity, accelerated mineral availability and increased buffering capacity; and biological benefits, such as increased nutrients for living organisms in the soil and enhanced biodiversity.
Sources of stable organic matter include crop residues, animal manure, compost, cover crops, and perennial grasses and legumes. Once a sufficient level of stable organic matter is attained, management practices to maintain that level include conservation tillage methods, rotating crops with perennial grass or legume sods, establishing legume cover crops and protecting soil from compaction. Stable organic matter also is influenced by the temperature, water capacity, type, drainage, fertility, pH and existing microbials of the soil.
To determine and monitor the level of stable organic matter in the soil, regular soil samples should be collected. In addition to the basic soil analysis, the WVU Soil Testing Lab offers organic matter determination soil analysis for a small cost. Through this analysis, organic matter is determined using the Loss on Ignition method and is reported in a percentage of weight. For more information regarding soil sampling, contact your local WVU Extension office.
By Jessica Hoover, WVU Extension Agent – Pendleton County