For example the graph to the left shows that soil analyses conducted by the University of Maryland Soil Testing Laboratory during 1996 showed only 31 percent of the samples contained phosphorus levels low enough to potentially limit crop productivity. The diagram below illustrates what happens to phosphorus in the soil. Crops take up phosphorus in a soluble form. These clay particles release phosphorus very slowly. This capacity of soils to fix phosphorus is one reason why levels of phosphorus in soil solution are usually low.
Crops take up phosphorus in a soluble form.
These clay particles release phosphorus very slowly. This capacity of soils to fix phosphorus is one reason why levels of phosphorus in soil solution are usually low. Some phosphorus is held in soil organic matter. This becomes available during decomposition when organic matter is broken down by soil microbes. In agricultural soils this process is accelerated if the soil is disturbed during cultivation.