What is responsible for decreased phosphorus availability in the soil?

Calcium phosphate precipitates play a significant role in decreasing phosphorus availability in the soil. When calcium ions are present in the soil, they can react with phosphate ions to form insoluble compounds, such as calcium phosphate. These compounds are not easily available for plant uptake, thus limiting the amount of phosphorus that crops can access. This precipitation process can occur in alkaline soils, where the solubility of calcium phosphate decreases, further exacerbating the issue of nutrient availability.

In contrast, organic matter decomposition typically contributes to the release of nutrients, including phosphorus, into the soil. Soil erosion can lead to the loss of the topsoil layer, which contains vital nutrients, but does not directly cause a decrease in available phosphorus itself. Excessive rainfall can lead to leaching, which may wash away soluble nutrients, including phosphorus, but it is not as directly impactful as the formation of calcium phosphate precipitates reducing phosphorus availability.