Certified Crop Advisor Practice Exam

The P index is used to determine if a manure or biosolids application should be based on which nutrients?

1. Only phosphorus

2. Only nitrogen

3. Both phosphorus and nitrogen

4. Neither phosphorus nor nitrogen

The correct answer is: Both phosphorus and nitrogen

The P index, or phosphorus index, is a critical tool used in nutrient management planning, particularly for assessing the risk of phosphorus runoff from agricultural fields. Its primary purpose is to evaluate the potential environmental impact of applying manure or biosolids based on phosphorus availability and the susceptibility of the surrounding landscape to phosphorus loss. Choosing to focus on both phosphorus and nitrogen acknowledges that while the primary concern of the P index is phosphorus, nitrogen’s presence can influence the effectiveness and environmental impact of manure applications. For instance, nitrogen can facilitate plant growth, thereby potentially utilizing the phosphorus, and its balance is relevant when considering nutrient application rates. While options that limit the focus to just one nutrient would be inadequate in addressing the comprehensive nutrient management strategies needed for sustainable agriculture. The combined evaluation helps ensure that nutrient applications are optimized for crop uptake and minimizes adverse environmental effects.