nutrients are lost through harvesting, leaching, prolonged wet
weather, melting snow, flooding and de-nitrification.
Sustainable agriculture involves returning nutrients to the soil
in the form of green manure, crop residues, composted manure and other
wastes to improve and maintain soil life.
During the growing season plants fix carbon dioxide by photosynthesis.
Around 20 to 25 percent of this fixed carbon is returned to the soil
through plant roots.
soil consists of fungi, microbes, earthworms, macrofauna and micro/mesofauna.
Agriculture involves not only the physical properties and mineral
structure of the soil, but also the process by which organic matter is
transformed into humus by microbes,
fungi, earthworms etc. Incorporating
crop residue and other organic mater into the soil promotes microbial
growth which in turn promotes humus production and soil fertility.