Persistent soil carbon enhanced in Mollisols by well-managed grasslands but not annual grain or dairy forage cropping systems

Abstract

Intensive crop production on grassland-derived Mollisols has liberated massive amounts of carbon (C) to the atmosphere. Whether minimizing soil disturbance, diversifying crop rotations, or re-establishing perennial grasslands and integrating livestock can slow or reverse this trend remains highly uncertain. We investigated how these management practices affected soil organic carbon (SOC) accrual and distribution between particulate (POM) and mineral-associated (MAOM) organic matter in a 29-y-old field experiment in the North Central United States and assessed how soil microbial traits were related to these changes. Compared to conventional continuous maize monocropping with annual tillage, systems with reduced tillage, diversified crop rotations with cover crops and legumes, or manure addition did not increase total SOC storage or MAOM-C, whereas perennial pastures managed with rotational grazing accumulated more SOC and MAOM-C (18 to 29% higher) than all annual cropping systems after 29 y of management. These results align with a meta-analysis of data from published studies comparing the efficacy of soil health management practices in annual cropping systems on Mollisols worldwide. Incorporating legumes and manure into annual cropping systems enhanced POM-C, microbial biomass, and microbial C-use efficiency but did not significantly increase microbial necromass accumulation, MAOM-C, or total SOC storage. Diverse, rotationally grazed pasture management has the potential to increase persistent soil C on Mollisols, highlighting the key role of well-managed grasslands in climate-smart agriculture.

Depth-dependent responses of soil organic carbon stock under annual and perennial cropping systems

“…Thus, the increased SOC stock under the pasture and the associated contribution from MAOM-C in Rui et al. ( 1 ) could be detected only for the topsoil, where plant C inputs are the highest. Moreover, SOC stock is positively correlated with the content of amino sugars solely in the topsoil, but it is negatively correlated with N -acetyl-β- d -glucosaminidase and polyphenol oxidase activities in the subsoil ( Fig.…”

“…Rui et al. ( 1 ) reported that perennial pasture with rotational grazing significantly increased soil organic carbon (SOC) stock at 0 to 30 cm by 15 to 28% compared to conventional continuous annual cropping systems in a 29-y field experiment in the north-central United States. We applaud their efforts in managing such a valuable long-term experiment as well as revealing the intriguing potentials to enhance SOC stock by promoting land conversion from annuals to perennials with optimized management.…”

Reply to Chen et al.: Soil organic carbon stocks and persistence of surface 30 cm of Mollisols

“…( 1 ) argue that “SOC stock is positively correlated with the content of amino sugars solely in the topsoil, but it is negatively correlated with N -acetyl-β- d -glucosaminidase and polyphenol oxidase activities in the subsoil.” Table S5 of ref. 2 showed the correlations between MAOM-C concentrations, not SOC stock, with soil microbial attributes. We believe using SOC or MAOM-C stock can help with soil C accounting purposes, but to unravel mechanistic relationships with soil microbial attributes it would be better to use SOC or MAOM-C concentrations.…”

“…Chen et al. ( 1 ) provide valuable feedback on our paper ( 2 ), suggesting that our work overestimated soil organic carbon (SOC) benefits of certain systems because we lacked data below 30-cm soil depth. In our paper, we acknowledged the uncertainties associated with deep soil C stocks, making no claim that our observations applied to deeper soils.…”

“…Similar trends were found when SOC and MAOM-C concentrations were analyzed with ANOVA, suggesting that cropping systems had significant effects across two depths, but with no system × depth interaction (table S2 of ref. 2 ). We acknowledged that results may vary with deeper soils.…”