• Soil Health
• Sustainability
• University of Saskatchewan

Objective

To estimate amounts of N2 fixed by free-living organisms in soil under annual tillage and minimum-tillage. To determine how soil zone and soil texture affect free-living N2 fixation. To determine how community structure and activity of free-living N2 fixing bacteria is affected by tillage management. To evaluate if/how annual climate affects structure and activity of free-living N2 fixing bacteria. To evaluate how soil moisture affects free-living N2-fixing community structure.

Outcome

This study measured free-living nitrogen fixation and the microorganisms responsible, in soils that have been under no-tillage management for varying amounts of time. In contrast to what we expected, the amount of time in no-tillage management did not affect the amount of free-living nitrogen fixation, and rates of nitrogen fixation were very low, ranging from 0.9 to 2.9 kg N ha-1 y-1. Only after 50 years of no-tillage management did we see an indication that these soils supported higher nitrogen fixation rates. Indeed, the highest nitrogen fixation rate measured in an agricultural field was measured in an annually tilled organic field not in a no-tillage field. The community of organisms responsible for nitrogen fixation was very diverse. Soils immediately adjacent to one another but under different management had different communities of organisms. The diversity of microorganisms capable of fixing nitrogen means that the soils are capable of responding to environmental fluxes. While these small sustained levels of nitrogen fixation are undoubtedly important in natural ecosystems, they should have no impact on fertility decisions made by farmers. 

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