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True soil fertility is the foundation for good crop and livestock performance. In natural eco-systems, the main sources of nutrients in the soil are air, water, rock minerals and organic matter.
In modern farming systems, chemical-based fertilisers have largely replaced the work that microbes do. Plants can be fed directly from the bag but being soluble, any fertiliser not used by the plant will either move through the soil into drainage water, or become “locked up” in soil reserve. Good examples of this are nitrates and phosphates, although potassium and other elements can be affected. Crops may respond to the use of fertilisers. However, releasing stored soil nutrients can help reduce costs, avoid pollution and improve productivity.
We know that soils contain enough nutrient reserves to feed plants for many years, if only the plant could gain access to them. In the past, little value was placed on the measurement of total soil reserves, as they were thought to be “locked-up” and unavailable to plants. Microbes play an important part in moving nutrients from “locked-in” resources because they have the ability to release these nutrients into forms that are truly plant-available; different types of microbes can pull nitrogen from the air, dissolve phosphates from rock and move minerals from the soil to the root zone.
Biological farming systems use this concept to match crop needs with soil reserves and microbial activity. The starting point for this is a full soil audit, which measures true fertility, chemistry balance and physical soil problems.
Standard soil tests, often done at low cost by fertiliser suppliers, are designed to look at the level of “available” Phosphate (P), Potassium (K) and Magnesium (Mg). These levels are determined by chemical extraction and the amount of extracted nutrient is then measured and said to be available to the plant.
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