What is a potential consequence of applying excessive nitrogen to crops?

Applying excessive nitrogen to crops can lead to increased risk of leaching into groundwater. This occurs because when nitrogen is applied in amounts that exceed what the plants can absorb, the excess nitrogen can be washed away by rainfall or irrigation. This leaching can lead to the contamination of groundwater with nitrate, which poses significant environmental and health risks.

Nitrate in groundwater can cause problems such as water quality degradation, which affects drinking water sources and can lead to health issues such as methemoglobinemia, or "blue baby syndrome," in infants. Furthermore, excessive nitrogen in the environment can contribute to algal blooms in nearby water bodies, leading to further ecological imbalances.

Meanwhile, the other options suggest benefits that would not necessarily result from excessive nitrogen application. While increased soil fertility and better crop yields may be initial outcomes of nitrogen application within proper limits, these benefits can diminish or become detrimental with excessive use. Enhanced photosynthesis may also occur within appropriate nitrogen levels, but over-application can lead to other stressors that compromise plant health. Therefore, the focus should remain on appropriate nitrogen management to avoid leaching risks and ensure sustainability in agricultural practices.