Certified Professional Horticulturist (CPH) Practice Exam

An active compost with a pungent odor is an indication that the compost is not getting enough...

1. Oxygen

2. Water

3. Carbon

4. Nitrogen

The correct answer is: Oxygen

A pungent odor in active compost indicates that the compost may not be getting enough oxygen. Composting is a biological process that relies on microorganisms, such as bacteria and fungi, to decompose organic materials. These microorganisms require oxygen to efficiently break down the materials, particularly during the aerobic composting process. When oxygen levels are low, anaerobic bacteria begin to dominate the decomposition process. These anaerobic conditions produce foul-smelling compounds, leading to a strong, unpleasant odor. Proper aeration—by turning the pile or using perforated containers—helps maintain oxygen levels, promoting a healthier composting environment. While the other options also play important roles in composting, they do not specifically correlate with the production of a pungent odor as directly as the lack of oxygen does. Insufficient water affects moisture levels but typically does not cause strong odors; imbalances in carbon or nitrogen affect microbial activity and the rate of decomposition but are not directly tied to odor unless they significantly disrupt aerobic conditions. Thus, oxygen deficiency is the primary reason for the pungent smell in compost.