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%), indicating that these management practices may promote nitrogen uptake in crops. 
  • Cover cropping may promote nitrogen uptake in crops due to the increased availability of soil N via nitrogen-fixing legumes and the decomposition of nitrogen-containing organic matter/residue.
  • Crop rotation may promote nitrogen uptake in crops due to carefully-timed plantings that coordinate soil nitrogen availability with either N-intensive or non-N-intensive crops.
• Reductions in N2O emissions were observed for both management practices (-5% and -4%, respectively), suggesting a reduction in denitrification and an increase in nitrogen use efficiency (NUE).

Enhanced efficiency fertilizers and 4R fertilization strategies (right source, rate, timing, and placement) 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 soil organic carbon (SOC) and crop yields, while simultaneously reducing N2O emissions and N leaching in the short-term

• Biochar amendments increased SOC by 27%, improved crop yields by 8.3%, and reduced N2O emissions by 40%. 
  • This 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.