Crop rotation and cover cropping can increase N uptake and C/N sequestration in soil, thereby reducing N2O emissions and N surplus

• Clear positive effects were observed for crop N in systems with cover cropping (+19%) and crop rotation (+11%). This could be attributed to the use of nitrogen-fixing legumes as cover crops and the preservation of soil N via timed plantings of N-intensive crops.
• Reductions in N2O emissions were observed for both management practices (-5% and -4%, respectively), suggesting a reduction in denitrification and increase in nitrogen use efficiency (NUE).

4R strategies and enhanced efficiency fertilizers can increase crop yield and crop N while reducing CO2, N2O, and NH3 emissions

• The use of enhanced efficiency fertilizers (including urease inhibitors, controlled release, and nitrification inhibitors) resulted in a 5.7% mean increase in crop yield and a 14% increase in crop N, indicating that these fertilizers are effective at providing crops with essential nutrients during important stages of growth. 
• Nitrification inhibitors may reduce N2O emissions by delaying nitrification until the crop has grown enough to absorb more nitrate, therefore increasing NUE and reducing denitrification. 
• Urease inhibitors and controlled-release fertilizers may reduce NH3 emissions by reducing overall soil ammonium concentrations.

Applying biochar has the potential to improve SOC and crop yields, while simultaneously reducing N2O emissions and N leaching in the short-term

• Biochar amendments increased soil organic carbon by 27%, improved crop yields by 8.3%, and reduced N2O emissions by 40%. 
• The observed stimulation in crop yield could be attributed to several factors, including biochar’s positive interactions with soil pH and cation exchange capacity. 
• Additional studies are needed in order to assess the long-term effects of biochar application. 

Organic N fertilizers can gradually build SOC and reduce N leaching, but may result in slight yield reductions and increases in N2O and CO2 emissions compared to soluble N fertilizers

• SOC may increase by ~1% per year under organic N fertilization, while N leaching may be reduced by as much as 43%, suggesting that the decomposition rate of organic N sources may better coincide with a crop’s ability to utilize available nutrients throughout the growing season. 
• Organic N fertilization may result in a slight decrease in overall crop yield (5%) and increase in both N2O (23%) and CO2 emissions (36%). These increases in emissions may be attributed to enhanced soil microbial activity.