Healthy soil should have abundant nitrogen to supply plant growth needs, but it should not all be in the inorganic fraction. Rather, organic nitrogen is the preferred storage warehouse from which soil microorganisms can decompose and release inorganic nitrogen to soil and then to plants. This system avoids leaching and volatile losses of nitrogen. Historically, scientists have had difficulty predicting how much nitrogen is made available to plants by soil biological activity due to time and resource constraints.
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Source: Phys.org