Response of soil health indicators to tillage is associated with soil mineralogy in maize-based agroecosystems across the U.S

The sensitivity of soil health indicators to tillage can be strongly influenced by agroecosystem context, leading to inconsistent responses of soil health indicators to tillage practices across sites. Using long-term maize-based tillage experiments encompassing a gradient of soil mineralogy across six U.S. states, we quantified differences in soil organic carbon (SOC) and additional soil health indicators of microbial biomass C (MBC) and N (MBN), mineralizable C (C min ), permanganate-oxidizable “carbon” (POXC), autoclave-extractable “protein” (ACE protein) and the activities of β-glucosidase (BG), N -acetyl-β-D-glucosaminidase (NAG), protease (PRO), phosphomonoesterase (PME) and arylsulfatase (SUL) between no-tillage and conventional (chisel or moldboard) tillage. To explain differences in soil health indicator sensitivity to tillage, we assessed (1) associations between SOC and soil health indicator inter- and intra-site responses to tillage, and (2) associations between mineralogy and soil health indicator responses to tillage on a soil versus SOC basis. The responses of soil health indicators to tillage were generally lower in magnitude when expressed on a SOC basis relative to a soil mass basis. However, indicator responses to tillage increased concomitantly with SOC response (1:1) across sites, except for (i) NAG activity, which was twice as sensitive to tillage as SOC (2:1), and (ii) POXC, which was half as sensitive to tillage as SOC (1:2). Within sites, the responses of soil health indicators to tillage were generally unaffected by SOC response. Metrics of reactive Fe and Al phases were generally the strongest predictors of SOC and soil health indicator responses to tillage, likely due to enhanced organomineral associations by these phases relative to other minerals. Our findings indicate that soil mineralogy can be used to further interpret the context dependency of the effects of tillage practices and potentially additional management practices on soil health and SOC.