Asymbiotic Nitrogen Fixation is Greater in Soils under Long‐Term No‐Till Versus Conventional Tillage

Abstract

A series of N‐rate experiments previously conducted in spring wheat, corn, and sunflower in North Dakota indicated that less N was required when fields were in six years or more continuous no‐till compared to conventional till. The objective of this study was to determine whether part of the reason for the decreased requirement for N was the greater activity of asymbiotic N‐fixing organisms. Twelve paired‐samplings were conducted in 2018. A surface 0‐ to 5‐cm deep sample was obtained in a long‐term no‐till field directly across the fence or road from a similar soil in conventional till. Samples were incubated in an acetylene‐reduction procedure to estimate N fixation rate. Ten of twelve paired samplings had greater asymbiotic N fixation compared to the conventional till counterpart. This indicates that long‐term no‐till soils support greater N production from soil microorganisms than conventional till soils, which would result in lower input costs to no‐till farmers.Core Ideas Microbial communities are different between conventional till and no‐till managed soils. Asymbiotic N‐fixation was greater in farmer‐managed no‐till than neighboring conventional till. N recommendations in long‐term continuous no‐till should be separate from conventional till N recommendations.