Organic matter matters because it serves many functions. Most importantly as an all-around fertiliser and soil conditioner. It also paves the way for nutrients to be accessible to the plants as they grow.
The biggest difference between soil and rock is the presence of organic matter and the associated biological activity that takes place in the former.
Organic matter, matters for maintaining soil health
The level of organic matter is highest in topsoil and with a few exceptions, it may decline dramatically with depth. New Zealand farmers and viticulturists respectively, regard the top 6 inches as their most productive soil. Topsoil is, therefore, a precious resource primarily due to the high level of organic matter and nutrients it contains relative to subsurface soil.
Once depleted, organic matter can take years to replace. With this in mind, adding natural residues and minimising topsoil loss through erosion and other forms of soil disturbance should be an important goal for every land manager.
Organic matter serves several functions, most importantly as an all-around fertiliser and soil conditioner and as a source of plant nutrients. Organic matter adds body to sandy soils and increases moisture and nutrient holding capacity. It promotes granulation in clay soils which helps with plant root penetration and maximises the ability for water and air to easily flow through the soil. It makes cultivation easier, resulting in better seedbeds, and reduces surface crusting that can affect new seedling growth.
The function of soil organic matter is broadly categorised into biological, physical, and chemical but they actually overlap and interact with one another.
Learn about the other functions of organic matter