I am a soil microbiologist and agronomist with more than 35 years of experience on aspects of sustainable management of agriculture and natural resources for increasing food security and environmental quality. Throughout my career, a topic that has continually attracted my attention and interest is nitrogen, an “intriguing enigma.” Nitrogen’s good side is that the nutrient is required for crop production. However, the element’s bad side is that excess amounts not used by plants go either into the groundwater as nitrate, or the atmosphere as nitrogen oxide, which can cause serious human and animal health problems and air pollution. The challenge is to optimize nitrogen (N) use while minimizing its negative impacts. We have been encouraging farmers to efficiently apply N fertilizer only when the crop requires it.