Final answer:
Alfisols are a soil order that has a high capacity to 'fix' soil phosphorus due to their high clay and organic matter content. They retain and fix phosphorus through processes such as adsorption and have a high cation exchange capacity (CEC).
Step-by-step explanation:
Soil orders are categories used to classify soils based on their properties and characteristics. One soil order that has a high capacity to 'fix' soil phosphorus is the Alfisols. Alfisols are soils that have developed under semi-humid to humid conditions and are found in many parts of the world, including the United States. They are typically rich in clay and organic matter, which contribute to their ability to retain and fix phosphorus.
One of the key mechanisms by which Alfisols fix phosphorus is through the process of adsorption. Clay minerals and organic matter in the soil have negatively charged surfaces that attract and hold onto positively charged phosphorus ions (PO43-). This prevents the phosphorus from being lost through leaching or runoff, making it available for plant uptake.
Additionally, Alfisols often have a high cation exchange capacity (CEC), which is a measure of the soil's ability to hold and exchange cations, including phosphorus. Soils with a high CEC can effectively retain nutrients like phosphorus and release them to plants as needed.