Controlled traffic farming effects on soil emissions of nitrous oxide and methane

Soil compaction affects soil aeration and gas diffusivity, and thus has a major impact on the release of greenhouse gases (GHGs) from fertilised soils. Controlled traffic farming (CTF) systems reduce the area of compacted soil by confining all field traffic to permanent traffic lanes, and a pilot trial at one long-term CTF site provided evidence of reduced soil emissions. We investigated the effect of CTF on soil emissions of nitrous oxide (N2O) and methane (CH4) using replicated manual chamber measurements in 3 traffic treatments; namely: non-trafficked CTF beds, permanent CT F lanes, and a single traffic pass on CTF beds to simulate the random traffic tracks of non-controlled traffic fanning. Emissions of N2O and CH4 were monitored fromm, these treatments in 15 crops over 3 years on 6 grain farms in Queensland, Victoria and Western Australia. This work has demonstrated that N2O emissions from trafficked soil were consistently and significantly greater (by an average factor of 2.2) than those from non-trafficked soil. At the same time, soil CH4 consumption was significantly increased in the CTF beds compared to random-trafficked or permanent traffic lanes, although overall CH4 fluxes were small. Permanent traffic lanes normally represent only 10%-15% of field area on controlled traffic farms, compared with similar to 50% or more trafficked area on non-controlled traffic farms. Thus, the results indicate that adoption of controlled traffic could reduce total soil emissions by 30%-50%. This demonstrates that CTF will reduce soil emissions of N2O and CH4 from mechanised crop production, while providing other agronomic, environmental and economic benefits.