A recent study published in Agriculture, Ecosystems and Environment provides valuable insights into the spatial variability of soil carbon dioxide (CO2​) and nitrous oxide (N2​O) fluxes in agricultural settings, highlighting the impact of management practices and offering recommendations for more accurate measurements. The research, conducted by a team including Nakian Kim, Chunhwa Jang, Wendy H. Yang, Kaiyu Guan, Evan H. DeLucia, and DoKyoung Lee, utilized a spatially high-resolution, multi-year dataset from commercial farms in central Illinois.  

The study emphasizes that understanding and mitigating agricultural soil greenhouse gas (GHG) emissions are crucial for achieving global climate goals. However, characterizing and predicting the spatial patterns of these fluxes requires extensive, high-resolution, and multi-year data, which has been limited until now.  

Researchers collected two years of in-season soil CO2​ and N2​O fluxes at a high spatial resolution across three commercial sites in central Illinois. One site used conventional continuous corn management, while the other two employed conservation practices in corn-soybean rotations.  

Key findings indicate that the spatial variability of CO2​ was relatively consistent across different sites, years, and management practices. However, N2​O showed significantly higher spatial variability, particularly in the conventionally managed site, where it was, on average, 77% more variable.  

The study also examined the contribution of N2​O “hotspots” – areas with disproportionately high emissions. While hotspots occupied a similar proportion of the sampling areas across conventional and conservation sites (12% and 13%, respectively), their contribution to field-wide emissions was greater in the conventional site (51%) compared to the conservation sites (34%). Furthermore, the spatial patterns of both gases, especially the location of hotspots, were inconsistent from year to year, with hotspots rarely appearing in the same place.  

According to the researchers, these results suggest that traditional field-scale monitoring using gas chambers may not be the most effective method for detecting GHG hotspots in row crop systems due to the unpredictable spatial heterogeneity influenced by management practices.  

Through sensitivity analysis, the study determined that reliable field-scale soil GHG flux estimates (with less than 25% error) are achievable when sampled above certain spatial resolutions: 1.6 points per hectare for CO2​ and 5.6 points per hectare for N2​O in their dataset. Lower spatial resolutions were found to be prone to underestimating field-wide N2​O flux.  

The study concludes that conventional practices, such as deep-chisel tillage and continuous corn with high nitrogen fertilization, may increase field-scale N2​O emissions and their spatial variability, making accurate monitoring more challenging. Conversely, CO2​ flux was more stable, requiring lower spatial resolution for monitoring. The inter-annual shifting of most GHG hotspots highlights the difficulty in predicting their location due to spatially heterogeneous management effects.  

For estimating field-wide emissions, the research suggests that a grid of chambers with a sufficient sample size, such as the identified thresholds for CO2​ and N2​O, can provide reliable results. The authors recommend that future measurement campaigns for soil GHG fluxes be designed considering management practices and the specific goals of the monitoring.  

This research was supported by the US Department of Energy ARPA-E SMARTFARM program.