Changes in soil organic carbon (SOC) storage have the potential to affect global climate; hence identifying environments with a high capacity to gain or lose SOC is of broad interest. Many cross‐site studies have found that SOC‐poor soils tend to gain or retain carbon more readily than SOC‐rich soils. While this pattern may partly reflect reality, here we argue that it can also be created by a pair of statistical artifacts. First, soils that appear SOC‐poor purely due to random variation will tend to yield more moderate SOC estimates upon resampling and hence will appear to accrue or retain more SOC than SOC‐rich soils. This phenomenon is an example of regression to the mean. Second, normalized metrics of SOC change—such as relative rates and response ratios—will by definition show larger changes in SOC at lower initial SOC levels, even when the absolute change in SOC does not depend on initial SOC. These two artifacts create an exaggerated impression that initial SOC stocks are a major control on SOC dynamics. To address this problem, we recommend applying statistical corrections to eliminate the effect of regression to the mean, and avoiding normalized metrics when testing relationships between SOC change and initial SOC. Careful consideration of these issues in future cross‐site studies will support clearer scientific inference that can better inform environmental management.

Agroforestry systems have been promoted as a solution to address trade-offs between environmental conservation efforts and the need for increased agricultural productivity on smallholder farms in Brazil. However, the impact of land use change from degraded pasture to agroforestry on soil properties remains unclear. The objectives of this research were to: (1) assess soil chemical, physical and biological properties across distinct land uses (degraded pasture, agroforestry and secondary forest); and (2) understand relationships between litter quality, soil organic matter (SOM) and key soil quality parameters in the Brazilian Atlantic Rainforest. Soils, macroinvertebrates and litter were collected in April and September of 2018 under five land uses, including: three types of agroforestry systems, a degraded pasture and a secondary forest in Sapucaia, Rio de Janeiro, Brazil. Our results showed that soil properties clearly separated the three agroforestry systems plots (AS1, AS2, AS3) from the forest and pasture plots. Moreover, litter quality and SOM likely influence multiple biological and physiochemical soil properties under agroforestry systems and secondary forest. Our findings suggest that agroforestry systems can help support soil biological, chemical and physical properties and that the litter quality may be an important driver of their effects and potential contributions to soil restoration in the region.

Crop production in water‐limited environments may be enhanced through improved soil function by facilitating precipitation capture and erosion control. Soil macrofauna are known to support improved soil structure and water dynamics through ecosystem engineering activities, and their populations can be influenced by management. We examined the effect of bare summer fallow frequency on soil macrofauna communities and soil physical properties in a long‐term (32‐yr) dryland no‐till agroecosystem experiment at two sites in eastern Colorado, USA. Treatments represented a gradient of fallow frequency and organic matter inputs, which included wheat ( Triticum aestivum L.)–fallow, wheat–corn ( Zea mays L.)–fallow, and continuously cropped with no planned summer fallow. The design also included a perennial grass treatment with minimal management consisting of six native grasses. We observed links between soil macrofauna and soil functional metrics, particularly related to soil aggregation and water infiltration. There was a trend toward higher macrofauna populations and soil function with increased cropping system intensity, and perennial grass outperformed the cropped treatments significantly for most soil health parameters. Multivariate analyses revealed that different treatments support relatively distinct macrofauna communities. Our results suggest that soil macrofauna populations may be important facilitators of soil structure and associated water dynamics in dryland no‐till agroecosystems and respond positively to reduced fallow and higher organic inputs.

Organic amendments are key sources of nutrients in croplands and play an important role in maintaining soil organic carbon (SOC) stocks. Stabilization of SOC is mediated by environmental and management factors and may differ between mineral‐associated organic carbon (MAOC) and particulate organic carbon (POC). To quantify these patterns, we conducted a global meta‐analysis evaluating SOC, MAOC, and POC responses to long‐term organic amendments (animal manure or crop residues) in annual cropping systems. Overall, organic amendments increased SOC, POC, and MAOC relative to unamended controls. When analyzed using effect sizes, POC exhibited greater proportional responses than MAOC or bulk SOC, reflecting the smaller baseline size of the POC pool. Responses across all SOC fractions were greatest when control treatments did not receive mineral fertilizer. Amendment effects were strongest in surface soils (<30 cm), when manure was applied rather than crop residues, and in studies with cumulative C inputs exceeding 15 Mg ha ^{− 1} . Analysis of absolute SOC stock changes (Δ Mg ha ^{− 1} ) revealed that MAOC accumulated carbon at approximately six times the rate of POC with increasing cumulative C inputs (0.06 vs. 0.01 Mg C ha ⁻¹ per Mg C input), indicating a substantially greater capacity for MAOC formation in annual croplands. These results demonstrate that repetitive C inputs drive the formation of MAOC, a more stable carbon pool critical for long‐term carbon storage.