Context: Under continuous long-term no-till farming, many silty soils develop platey and massive compacted structures in topsoil, ascribed to low crop diversification and intense agricultural traffic. Aims: We hypothesise that agricultural scenarios of greater diversification and cropping intensity should increase carbon (C) inputs and total and particulate organic C, resulting in the disappearance of these platey and massive compacted structures and soil compaction. Methods: The hypothesis was tested in 55 selected production fields (lots or macro-plots of trials with a cultivated area greater than 15 ha) and five non-cultivated sites across the Rolling Pampas of Argentina. The whole area was covered by fine, illitic, thermal, silty loams (Typic Argiudolls, US Soil Taxonomy; Typic Phaeozems, FAO Soil Map). Based on estimations of the crop intensity index (CII; proportion of days in the year with active crop growth) and recent agricultural history of crop sequences, sampled fields were grouped into five categories: soybean (Glycine max) monoculture (CII < 0.45; mean CII = 0.39); low intensity cropping sequence (CII = 0.45–0.60; mean CII = 0.50); high intensity cropping sequence (CII = 0.60–0.80; mean CII = 0.66); pastures for hay bale production (CII = 1.0); and quasi-pristine situations (areas with non-implanted and non-grazed grass vegetation or with negligible stocking rate, CII = 1.0). Key results: Total C inputs to soil varied within ~1400–7800 kg C ha−1 year−1 and were significantly and positively related to crop intensity index (P < 0.0001, r = 0.83). The highest (P < 0.05) soil organic C levels were observed in the first 0.05 m of soil and quasi-pristine conditions (even higher than under pasture), and the lowest (P < 0.05) under soybean monoculture. In the 0.05–0.20 m soil layer, quasi-pristine conditions had significantly (P < 0.05) higher soil organic C levels; the other situations did not differ. Soil organic C and particulate organic C levels (0–0.05 m layer) were related to both CII and annual C input. Platey structures and clods >0.1 m (0–0.2 m layer) were negatively related to CII (r = −0.59 and −0.45, respectively; P < 0.0001) and C inputs from crops (r = −0.60 and −0.29, respectively; P < 0.01). Nevertheless, this did not result in soil compaction alleviation, as shown by soil bulk density, maximum penetration resistance and water infiltration variations. About 92% of the samples with soil bulk density above the threshold (1.35 Mg m−3), and about 32% of the total records, presented levels of maximum penetration resistance, aeration porosity and/or water infiltration beyond the values suggested as critical. Conclusions: Although soil organic C in topsoil varied as hypothesised, the studied soil physical properties did not. This partially rejects our hypothesis. Implications: This study underscores the intricate interplay between crop intensity, SOC enhancement, soil structure improvement and the persistent challenge of subsoil compaction.

Black Soils of Argentina are dominant in the Pampas region and are key to its economy because they support most of its grain production, and livestock for

Long-term soil organic carbon (SOC) monitoring provides a rare opportunity to test the performance of process-based models against real data. We evaluated RothC using 20 georeferenced soil profiles sampled in 2004 and 2024 in the semi-arid steppe of Central Kazakhstan. We used the 2004 SOC stocks for equilibrium initialization, whereas independently measured 2024 stocks were used for endpoint evaluation. A baseline-conditioned, endpoint-uncalibrated forward simulation (S1) was driven by profile-specific climate, NPP-scaled plant-C inputs, vegetation cover, and reconstructed management; a constrained inverse analysis (S2) estimated the non-negative effective C-input multiplier required to reproduce the observed endpoint, and a zero-input simulation (S3) defined the lower feasibility boundary. S1 preserved the broad between-profile variation in absolute 2024 SOC stocks (R² = 0.692), but agreement for the observed 2004–2024 SOC change was negligible (R² < 0.001; Lin’s CCC = 0.002). The direction of SOC change was reproduced at 9 of the 20 profiles, with an RMSE of 12.49 Mg C ha⁻¹ and a mean bias of −4.41 Mg C ha⁻¹. We obtained physically admissible inverse solutions for 17 profiles, with M_required ranging from 0.42 to 4.62 (mean = 2.04; median = 1.96). Profiles 295, 299, and 313 remained below the zero-input boundary under all management-timing scenarios. Together, these results show that adjusting plant-C input can reconcile modeled and observed SOC at most profiles. However, no non-negative adjustment of plant-C input could reproduce some observed endpoints. These cases indicate that other processes or sources of uncertainty should be considered.