Increased abundance of arbuscular mycorrhizal fungi in response to low phosphorus fertility may support crop yields under long‐term no‐till management

No‐till practices positively affect soil microorganisms that mobilize P, and thus the soil test phosphorus (STP) concentration needed to optimize crop yield may be reduced compared to current university recommendations. However, the effects of STP concentrations on soil microorganisms and their relation to crop yields are not sufficiently documented. This 5‐year study in a long‐term no‐till field near Pierre, SD, was conducted to (1) determine the effects of STP concentrations on crop yields, soil microbial communities, and arbuscular mycorrhizal (AM) fungal abundance, (2) evaluate ergothioneine (ERGO) content of harvested seed as an indicator of AM fungal abundance and activity, and (3) compare methods for identifying differences in AM fungal soil abundance. From 2018 to 2022, crop yields were similar among the STP concentration categories. However, numbers of soil AM fungal propagules in the lowest STP category (5.9 propagules/g soil) were significantly greater than the medium and very high STP treatments (1.8–2.0 propagules/g soil). ERGO content in harvested seeds was also greater in the low compared to medium and very high STP categories. Phospholipid fatty acid results were inconclusive as total soil fungi and bacteria and relative abundances of their subsets, including biomarker 16:1ω5 for AM fungi, were significantly different among STP treatments in only 1 of 5 years. Greater amounts of indicators of AM fungal abundance and activities in the low STP category may be the reason for similar crop yields regardless of STP category concentration, suggesting the need to re‐evaluate P recommendations in no‐till systems.