Garden with Insight v1.0 Help: loosely/tightly bound/held

We use these terms both for nutrients in organic matter and for nutrients in mineral deposits.

In organic matter
Nutrients tightly held to organic matter are incorporated in complex molecules such as proteins and are only released when these molecules are absorbed by soil microbes and digested. Nutrients loosely held in organic matter are in smaller molecules with oxygen, hydrogen and carbon or are adsorbed to clay or organic matter particles at cation exchange sites. Plants depend on release of tightly held and loosely held nutrients so that they can absorb them. A healthy soil microbial community is essential for release of nutrients from organic matter.

In this simulation nitrogen moves between loosely held (active) and tightly held (stable) forms in organic matter by an equilibrium equation based on the long-term cultivation of the soil. The simulation makes no such distinction between loosely and tightly held phosphorus in the organic matter, because phosphorus tends to be held much more tightly in organic compounds than is nitrogen (therefore it is never "loosely held").

In mineral deposits
Nutrients tightly held in mineral deposits are found in large mineral particles (rocks) that break down over very long periods of time. Nutrients loosely held in mineral deposits are in smaller particles (in sand grains, for example) or rocks that break down more quickly. Different types of mineral deposits break apart at different rates; this produces some of the variation in different soil types.

Nitrogen in mineral deposits is not simulated here because very few mineral deposits contain significant amounts of nitrogen, and thus over 99% of nitrogen in the soil is usually contained in organic matter. However, in mineral deposits the distinction is made between loosely and tightly held phosphorus. This is because phosphorus appears in many mineral deposits of varying types.

How it works:
nutrient cycling