Surface-applied fertilizer places a concentration of soluble nutrients on the soil surface. The soil surface might already be enriched due to past practices such as surface placement of fertilizer or manure, nutrients from residue breakdown, and reduced tillage management systems. Termed “stratification,” this enriched zone has less capacity to stabilize applied phosphorus, thus elevated nutrient losses can occur with future rainfall events.
The loss can be via three paths in Ohio fields:
1. Direct surface runoff to the ditch can occur.
2. Surface water can move to surface drainage features such as surface drains or catch basins.
3. Preferential flow paths allow water to quickly enter subsurface drainage. Preferential flow from macropores is the result of “biological activity (e.g., root channels, worm holes, etc.), geological forces (e.g., subsurface erosion, desiccation, and synaerisis cracks and fractures) or agrotechnical practices (e.g., plowing, bores, and wells). Surface cracks and channels that bypass the root zone are also responsible for rapid transport of moisture and chemicals through the unsaturated zone”
Figure 14. Surface condition where DRP losses were increase by 4X. Source: Kevin King.