Two major ways in which soil organic matter is depleted are application of inorganic fertilizers and intensive use of tillage.  Inorganic fertilizers (especially nitrogen) act like steroids for soil microbes, unnaturally stimulating reproduction of certain species, which in turn accelerates the decomposition of organic matter they feed on.  Inorganic fertilizers are steroid-like because they are “immediately available,” unlike organic fertilizers, which release their nutrients more slowly over an extended period as needed by the growing crop.  Intensive tillage breaks up the soil surface and exposes soil organic matter to air, which also speeds its decomposition.  There are many different types of tillage, with greatly varying impacts on the soil.  The most intensive form of tillage is moldboard plowing, which turns over the top 10-12” of soil or deeper to prepare a field for planting.  On the other hand, harrows drag numerous tines through a field to physically uproot small weeds, a much less intensive form of tillage that disturbs only the top few inches of soil.  Both industrial and organic farmers often plow to prepare a field for planting.  Organic farmers are more likely to conduct light tillage operations for weed control, while industrial farmers spray synthetic herbicides.

Industrial farmers deplete soil of organic matter via intensive tillage and heavy use of inorganic fertilizers.  And this organic matter is not replenished unless they employ organic practices such as cover crops or utilize soil-restoring crop rotations, which cannot always undo the damage done by harsh tillage and chemicals.  The genius of organic agriculture is that heavy inputs of organic matter equal and often exceed the losses caused by tillage, meaning that organic matter content is increased or at least maintained in organic farming systems.

Tillage is quite common in industrial agriculture (particularly in corn cultivation), but over the past several decades more and more farmers have reduced their tillage intensity by switching to farming methods known collectively as “conservation tillage.”  Conservation tillage methods are less disruptive to the soil, and include no-till, which does away with the plow altogether.  In the 1980s, USDA made farmers’ subsidies dependent upon their adoption of conservation tillage methods, the major factor responsible for reduced soil erosion in American agriculture through the mid 1990s.