Which nutrient is most likely to accumulate in the top 6 inches of the soil if over applied?

Phosphorus is the nutrient that is most likely to accumulate in the top 6 inches of the soil if over-applied. This accumulation can occur because phosphorus is less mobile in the soil compared to other nutrients. Once added to the soil, phosphorus tends to bind with soil particles, especially in high pH environments, making it less soluble and less available for leaching.

When excessive phosphorus is applied, such as through fertilizers, it can remain concentrated in the upper soil layers, particularly near the surface where the root systems of plants are active. This can lead to environmental concerns, particularly regarding water quality, as phosphorus runoff can contribute to eutrophication in nearby water bodies.

In contrast, nitrogen is more mobile and can percolate deeper into the soil profile, while potassium and calcium also have different behaviors concerning leaching and movement in the soil. Thus, the distinctive retention characteristics of phosphorus make it the nutrient most likely to accumulate in the top layers if applied in excess.