Why are sulfur-coated urea or urea formaldehyde included in nitrogen fertilizers?

Sulfur-coated urea and urea formaldehyde are included in nitrogen fertilizers primarily because they are designed to provide a slow-release source of nitrogen. This slow-release capability helps in minimizing nitrogen loss to the environment, particularly through leaching, and allows for a more sustained release of nutrients over time.

This gradual release of nitrogen is advantageous for plant health, as it matches the nitrogen availability to the uptake capacity of the plants, reducing the risk of nutrient burn and promoting more healthy and efficient growth. By ensuring that nitrogen is available steadily, these fertilizers help maintain optimal soil nutrition levels for crops, enhancing overall agricultural productivity.

In contrast, the other choices do not accurately reflect the primary role of these fertilizers. Minimizing soil pH is not a function of sulfur-coated urea or urea formaldehyde; in fact, their impact on pH varies based on various factors. Additionally, urea is primarily a source of nitrogen rather than potassium, and while improvements in soil structure can be beneficial, this is not a direct function of the slow-release characteristics of these nitrogen fertilizers.