Certified Crop Advisor Practice Exam

How does growing a legume in rotation affect nitrogen fertilizer rates for a grain crop?

1. Increases the rate

2. Reduces the rate

3. No effect on the rate

4. Double the rate

The correct answer is: Reduces the rate

Growing legumes in rotation with grain crops positively impacts nitrogen management in cropping systems. Legumes have the unique ability to fix atmospheric nitrogen through a symbiotic relationship with specific bacteria in their root nodules. This biological nitrogen fixation contributes to increased soil nitrogen levels. As a result, when a grain crop follows a legume in a rotation, the available nitrogen from the decomposed legume biomass and the nitrogen fixed during the legume's growth can reduce the need for synthetic nitrogen fertilizers. This is particularly beneficial for crops that traditionally require higher nitrogen input. By incorporating legumes into the rotation, farmers can rely on the natural contribution of nitrogen, leading to reduced nitrogen fertilizer application rates for the subsequent grain crop, promoting both cost savings and environmental sustainability by minimizing risks of nitrogen leaching and runoff.