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

Authors: WINTER, CLARENCE - South Dakota State University; GAUTAM, ASMITA - South Dakota State University; APPEL, AMANDA - South Dakota State University; LEWIS, BRENNAN - South Dakota State University; BECK, DWAYNE - Retired Non ARS Employee; XU, SUTIE - South Dakota State University; Lehman, Richard; CLARK, JASON - South Dakota State University

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/16/2026
Publication Date: 7/31/2026
Citation: Winter, C., Gautam, A., Appel, A., Lewis, B., Beck, D., Xu, S., Lehman, R.M., Clark, J. 2026. Increased abundance of arbuscular mycorrhizal fungi in response to low phosphorus fertility may support crop yields under long-term no-till management. Soil Science Society of America Journal. 90(4). Article e70313. https://doi.org/10.1002/saj2.70313.
DOI: https://doi.org/10.1002/saj2.70313

Interpretive Summary: Phosphorus (P) is a costly and necessary input for crop production. Moreover, applied P may be lost from fields due to soil erosion and drainage. Reducing the amount of P while maintaining crop yields saves input costs and reduces the potential of P loss from the field. No-till cropping practices may decrease soil test P (STP) levels needed to optimize crop yield due to positive influences on beneficial soil microorganisms that mobilize P. Tillage and elevated soil P levels often inhibit soil microorganisms that mobilize soil P. However, the effects of STP levels on soil microorganisms and their relation to crop yields are not sufficiently documented to support revised STP recommendations for no-till systems. This five-year study in a long-term no-till field near Pierre, SD was conducted to 1) determine the effects of STP levels on crop yields and soil microbial communities, particularly arbuscular mycorrhizal (AM) fungi, and 2) determine the relative efficacy of methods to identify differences in AM fungal soil inoculum potential due to STP level. From 2018 to 2022, there were no economically significant crop yield increases with increasing STP levels. However, the lowest STP level had significantly greater numbers of soil AM fungal propagules (5.9 propagules g-1 soil) compared to the medium (2.0 propagules g-1 soil) and very high STP treatments (1.8 propagules g-1 soil). Analysis of soil microbial communities using a biochemical assay were inconclusive as total soil fungi and bacteria and relative abundances of their subsets, including a biomarker for AM fungi, were significantly different among STP treatments in only one out of five years. Ergothioneine content in harvested seeds, a potential indicator of AM fungal biomass and activities, was greater in the low STP category compared to medium and very high STP categories. This study indicates the need to evaluate P recommendations in no-till crop production systems and provides evidence that changes in soil biology may enable competitive yields under low STP, while saving input costs and reducing loss of P from land.

Technical Abstract: No-till practices may lower the soil test phosphorus (STP) level needed to optimize crop yield due to positive influences on beneficial soil microorganisms that mobilize phosphorus. However, the effects of STP levels on soil microorganisms and their relation to crop yields are not sufficiently documented to support revised P recommendations for no-till systems. This five-year study in a long-term no-till field near Pierre, SD was conducted to 1) determine effects of three STP levels on crop yields and soil microbial communities, particularly arbuscular mycorrhizal (AM) fungi, and 2) determine the relative efficacy of methods to identify differences in AM fungal soil inoculum potential due to STP level. From 2018 to 2022, there were no economically significant crop yield increases among the three STP categories. However, numbers of soil AM fungal propagules in the lowest STP (5.9 propagules g-1 soil) were significantly greater than the medium (2.0 propagules g-1 soil) and very high STP treatments (1.8 propagules g-1 soil). Phospholipid fatty acid results were inconclusive as total soil fungi and bacteria and relative abundances of their subsets, including biomarker 16:1'5 for AM fungi, were significantly different among STP treatments in only one of five years. Ergothioneine content in harvested seeds, a potential indicator of AM fungal biomass and activities, was greater in the low STP category compared to medium and very high STP categories. This study indicates the need to evaluate P recommendations in no-till systems and provides evidence that changes in soil biology may enable competitive yields under low STP.