Using Nitrogen Smartly: Part 7

Humus contains about 10% nitrogen (N). As the humus content builds up in the soil, so does the N reserve stored in it. However, this N is locked into the humus and released only when the humus breaks down.

- Bill Kerr

When a farmer cultivates virgin soil, the humus content built up over many years starts to break down due to aeration, stimulating the bacteria to feed on the organic material. The process releases N for uptake by plants.

This explains why the farmers who initially cultivated vast areas of South Africa for the production of maize and wheat had to add much less N to soil for high yield.

To maintain the organic content, and so retain the benefits of humus, you can try to provide the soil with raw organic matter in the form of crop residue and/ or manure and compost.

Depending on the crops grown, the climate and the soil type, the humus content should stabilise at a sustainable level.