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Organics and Soil Carbon

For related articles and information, please visit OCA's Environment and Climate Resource Center page and our Organic Transitions page.

This paper explains how atmospheric carbon is introduced into the soil and how it is stored in stable forms. It identifies the farming techniques that are responsible for the decline in soil carbon and gives alternative practices that do not damage carbon. Increasing soil carbon will ensure good production outcomes and farm profitability. Soil carbon, particularly the stable forms such as humus and glomalin, increases farm profitability by increasing yields, soil fertility, soil moisture retention, aeration, nitrogen fixation, mineral availability, disease suppression, soil tilth and general structure. It is the basis of healthy soil.

Organic agriculture also helps to reduce greenhouse gases by converting atmospheric carbon dioxide (CO 2 ) into soil organic matter. Some forms of conventional agriculture have caused a massive decline in soil organic matter, due to oxidizing organic carbon by incorrect tillage, the overuse of nitrogen fertilizers and from topsoil loss through wind and water erosion.

Why is carbon important to productive farming?
Soil carbon is one of the most neglected yet most important factors in soil fertility, disease control, water efficiency and farm productivity. Humus and its related acids are significantly important forms of carbon. Below is a summary of the benefits of humus

Humus improves nutrient availability:

· Stores 90 to 95% of the nitrogen in the soil, 15 to 80% of phosphorus and 20 to 50% of sulphur in the soil
· Has many sites that hold minerals and consequently dramatically increases the soil's TEC (total exchange capacity or amount of plant available nutrients that the soil can store)
· Stores cations, such as calcium, magnesium, potassium and all trace elements
· Prevents nutrient leaching by holding them
· Organic acids (humic, fulvic, ulmic and others) help make minerals available by dissolving locked up minerals
· Prevents mineral ions from being locked up
· Encourages a range of microbes that make locked up minerals available to plants.
· Helps to neutralize the pH
· Buffers the soil from strong changes in pH

Humus improves soil structure:
· Promotes good soil structure which creates soil spaces for air and water
· Assists with good/strong ped (soil particle) formation
· Encourages macro-organisms (ie earthworms and beetles etc) that form pores in the soil.

Humus directly assists plants:
· The spaces allow microorganisms to turn the nitrogen in the air into nitrate and ammonia
· Soil carbon dioxide contained in these air spaces increases plant growth
· Helps plant and microbial growth through growth stimulating compounds
· Helps root growth, by making it easy for roots to travel through the soil     


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