Certified Crop Advisor Practice Exam

Which loss pathway is most concerning for the loss of phosphate from recently tilled soil?

1. Leaching

2. Runoff

3. Erosion

4. Volatilization

The correct answer is: Erosion

Phosphate loss from recently tilled soil is primarily a concern due to erosion. When soil is tilled, its structure is disturbed, which can lead to increased erosion by wind and water. This process can remove the nutrient-rich topsoil where phosphate is often concentrated. Erosion can carry away not only soil particles but also the attached phosphates, resulting in significant nutrient loss from the agricultural system. Additionally, phosphate has low solubility in water, which makes it less prone to leaching compared to more soluble nutrients. This characteristic means that leaching is generally not as significant a pathway for phosphate loss as erosion, particularly in tilled soils. Runoff can carry away particulate matter, including phosphate, but erosion is generally the more concerning factor, especially after tillage. Volatilization primarily affects certain nitrogen forms, not phosphates, so it is not a relevant concern for phosphate loss.