ABSTRACT Improvement of soil structure is critical for efficient nutrient and water transport to plants, particularly in sodic, dispersive soils. In addition to inorganic amendments such as gypsum, organic amendments (OAs) can enhance soil aggregation and stability through biochemical processes, but it is unclear how OAs composition [carbon (C) content, C: nitrogen (N) ratio and C functional groups] influences aggregation in sodic subsoils. To address this, we conducted a 17‐month soil incubation study in which 19 organic and inorganic amendments were vertically banded in an alkaline sodic subsoil (collected from 20 to 40 cm depth). The study examined how OA properties and their decomposition affected aggregate formation and stability (indicated by wet mean weight diameter; WMWD), via changes in soil physiochemical and biological properties at 3 and 17 months. At 3 months, aggregate stability correlated positively with total C content and C quality of the OAs (i.e., aliphatic C, C/N ratio), and soil microbial biomass C. The highest increase in aggregate stability (2–2.5‐fold) was observed in soils amended with plant residues, including reed ( Phragmites australis ), faba bean ( Vicia faba L.) and wheat ( Triticum aestivum L.). By 17 months, these beneficial effects on aggregation largely diminished. Chicken manure improved soil aggregation in the short term (3 months) and maintained higher N availability in the long term (17 months), indicating its potential use to address multiple subsoil constraints. In contrast, neither gypsum nor polyacrylamide improved soil aggregation. Our findings support the use of vertically banded plant and animal manure‐based OAs to improve sodic subsoil structure and biological functions of sodic subsoils, with implications for soil function and agricultural productivity.

ABSTRACT The Caatinga biome, South America's largest tropical dry forest, faces critical degradation due to extensive land‐use changes, particularly through the conversion of native vegetation into pasture and subsequent pasture degradation. Agroforestry systems (AFS) have been proposed as sustainable alternatives for rehabilitating these degraded landscapes by improving vegetation structure, biomass productivity and soil functionality. This study evaluated the effects of four contrasting land‐cover systems: (i) preserved native Caatinga vegetation (reference ecosystem), (ii) long‐term pasture dominated by Urochloa brizantha , (iii) low‐density agroforestry with widely spaced tree–crop arrangements and (iv) high‐density agroforestry with structurally complex and closely spaced woody components—on ecosystem multifunctionality, aboveground biomass production, litter deposition, litter nutrient content and key soil fertility and carbon parameters in Oxisols of the Brazilian tropical seasonal dry forest. We hypothesized that habitat simplification through land‐use intensification reduces above‐ and belowground ecosystem functionality by impairing carbon cycling, nutrient dynamics and soil structure. Our findings support this hypothesis, showing that the natural ecosystem exhibited the highest aboveground biomass (22.47 t ha −1 ), litter deposition (849.98 kg ha −1 ) and litter C, N and P contents (357.40, 10.88 and 3.16 g kg −1 , respectively), significantly outperforming managed systems. Among agroforestry systems, high‐density configurations showed significantly higher biomass production (69.76% greater) and improved soil fertility parameters—soil pH (17.65% higher), SOC (18.75% higher), K + (129.41% higher) and Ca 2+ (57.43% higher)—compared to low‐density systems ( p < 0.05). Soil analyses revealed that the natural ecosystem had superior levels of light fraction organic matter, humic substances and total soil organic carbon, alongside lower bulk density and higher acidity. Conversely, pasture had the highest particulate organic carbon and SOC stock, suggesting contrasting carbon stabilization pathways under different land uses. Principal Component Analysis (PCA) distinguished land covers based on multidimensional litter and soil traits, with key indicators such as pH, base cations (Ca 2+ , Mg 2+ ), organic carbon fractions and litter nutrient contents explaining much of the variance. These results highlight that complex vegetation systems, including high‐density agroforestry, maintain better soil and biomass functionality than simplified land uses. The study contributes valuable insight into sustainable land management practices aligned with the United Nations Sustainable Development Goal 2 (Zero Hunger), emphasizing the need for multifunctional systems to restore ecosystem services and improve productivity in semi‐arid regions like the Caatinga.

ABSTRACT Analysing land‐use pattern changes and their associated carbon footprint is essential for achieving sustainable development. Based on the PLUS‐InVEST model, this study conducted a comprehensive analysis of land use change, land‐use structural conflicts and associated carbon storages (CSs) and carbon emissions (CEs) in the Longnan region of Gansu Province, China. The results show that over the past 20 years, cultivated land has continuously decreased, while built‐up land increased at the fastest rate. Land‐use structure conflicts were predominantly at the two lowest levels (> 90%). From 2020 to 2050, land‐use change trends will diverge significantly across multiple scenarios. CSs show a persistent declining trend, both historically and under all future scenarios. From 2000 to 2020, net CEs steadily increased, with significant spatial distribution differences, and the decoupling between land‐use structure and CEs showed initial improvement. This study provides an integrated perspective on CSs and CEs. It pioneers the analysis of decoupling land‐use structure from CEs, providing a solid research foundation and empirical reference for Longnan and analogous mountainous regions.

ABSTRACT Particle detachment is a key sub‐process in soil erosion, and its rate can increase in croplands irrigated with brackish or saline water. Despite this adverse effect on soil, no studies have explored the impact of Sodium Adsorption Ratio (SAR, a key parameter measuring sodium excess among the exchangeable cations in soil) on rill erosion, the most common form in steep and long hillslopes. To fill this gap, this study has evaluated the changes in rill detachment capacity (hereafter ‘D c ’), rill erodibility (K r ) and critical shear stress (τ c ) of soils sampled in Northern Iran at five values of SAR compared to the soil with a very low sodium concentration. The simulations of the rill detachment process in flume experiments have shown that: (i) a SAR of 7.13 mmol/L 1/2 is the threshold resulting in a significant increase in D c ; (ii) over this limit, D c increases by percentages between 150% (SAR = 14.3 mmol/L 1/2 ) and 300% (SAR = 27.2 mmol/L 1/2 ); (iii) D c is not correlated to soil aggregate stability, and its increase may be explained by the decrease in van der Waals' forces binding together the soil particles; (iv) also K r noticeably increases with SAR over 7.13 mmol/L 1/2 until a maximum value measured at the highest SAR values of this study; (v) in contrast, the variability in τ c with SAR is not monotonic, this parameter showing a minimum value in soils with SAR of 7.13 mmol/L 1/2 and increases at the extreme values of SAR (0 and 27.2 mmol/L 1/2 ). Overall, the study indicates that the risk of rill erosion noticeably increases in soils treated with brackish or saline water, and, therefore, the use of irrigation water with SAR lower than seven is suggested to land managers.

ABSTRACT The southeastern Amazon region represents one of the critical hotspots of land‐use change (LUC) in Brazil. Conversion of natural ecosystems to agricultural fields triggers mineralization of soil organic matter and decomposition of residual forest biomass, releasing large amounts of nitrogen (N) that, together with subsequent high N‐fertiliser applications, disrupt N biogeochemical cycles. Therefore, we hypothesize that deforestation disrupts surface soil N‐pools, causing their gradual percolation into deeper layers of these highly weathered tropical soils. To test this, we measured total‐N and key fractions—particulate organic matter N (POM‐N), mineral‐associated organic matter N (MAOM‐N), water‐extractable N (WEN), ammonium (NH 4 + ‐N) and nitrate (NO 3 − ‐N)—to 800 cm depth in forest, recently deforested, single‐crop soybean and double‐crop soybean–corn systems in Mato Grosso, Brazil. Compared to the forest, the deforested site showed a 40% reduction in soil total‐N stocks at 10 cm; however, it was 62% higher at depths of 100–300 cm. In the croplands, the soil total‐N stocks remained similar to those in the forest. The POM‐N was nearly absent in the deforested site, whereas the MAOM‐N was consistently lower in both croplands and deforested soils than in the forest. The deforested site had the highest WEN and inorganic‐N (NH 4 + ‐N and NO 3 − ‐N) stocks to 800 cm, with most concentrated in the top 0–200 cm. Croplands had the greatest NO 3 − ‐N stocks at 300–600 cm. Principal component analysis (PCA) showed that WEN and inorganic‐N in the top 100 cm clustered with the deforested site, whereas POM‐N, MAOM‐N and total‐N at the surface clustered with the forest. Below 100 cm, the soil total‐N stock was clustered with the deforested site. These results provide critical insight into the initial mechanism of deep nitrate formation: the breakdown of the N biogeochemical cycle after deforestation, fueled by decomposition and N mineralization from soil organic matter and remaining forest biomass following slash‐and‐burn events on the Amazon–Cerrado agricultural frontier. However, further studies are needed to confirm the spatial and temporal persistence of these patterns across the region.

ABSTRACT Transforming agricultural waste into biochar can potentially generate renewable energy, capture carbon, improve soil health, and mitigate climate change. However, its adoption is still minimal due to ambiguity in the realisation of associated benefits, as the evidence of its impact on crop yield based on on‐farm data is very limited. In this study, we analysed a comprehensive dataset of 962 households across three states of India, viz. Madhya Pradesh, Maharashtra, and Odisha. Findings show that the application of biochar had a positive and significant effect on crop yield enhancement (4.34%) and net return (29.34%), and a reduction in cost of cultivation (1.52%). However, the effect size is much smaller than that reported in experimental studies conducted in controlled conditions. Farmers who are more experienced in farming, have irrigation facilities, and diversify crops and enterprises perceive benefits from biochar. Improvement in soil fertility is the primary benefit farmers perceive from biochar, whereas the limited availability of biochar and lack of incentives are the major constraints in adoption. The study suggests strategies and policies for outscaling and creating enabling environments for biochar production in Indian agriculture.

ABSTRACT Improving soil organic matter contents in semi‐arid zones reduces the risk of soil degradation and improves climatic resilience. As a technique for the recarbonisation of abandoned or degraded soils, applications of massive amounts of exogenous biomass (EB) such as wood chips have not been widely tested, and agronomic integration is still lacking. While it has been shown that sweet potato ( Ipomea batatas ) may be able to overcome nitrogen (N) limitations provoked by massive applications of EB, the exact mechanism is not clear. In a field experiment in Valencia (Mediterranean, semi‐arid climate), we mixed in the soil profile (0–30 cm) an equivalent of 150 t ha −1 ramial chipped wood (RCW) before sweet potato cultivation, set up in two adjacent fields with long‐term management histories (15 years) of abandonment versus organic farming. RCW incorporation in plots led to increased concentrations of soil organic carbon (SOC) in the fine earth fraction, which was greater in organically managed plots; whereas average SOC increased from 13.3 to 17.2 g kg −1 in the abandoned plot, it increased from 16.0 to 27.4 g kg −1 in the organically managed plot. Furthermore, despite greater initial SOC contents in organically managed plots, soil stabilisation of C (and N) was greater in relative terms as well, with an average SOC increase of 68%, as compared to only 29% in abandoned plots. Sweet potato leaf N content was not associated with measured soil N species; however, management history was relevant, since N nutrition was improved in the organic field by 0.44%–0.73% (w/w) over the growing season, and those plants in the abandoned field contained about 20% more N derived from the atmosphere (N dfa ). Sweet potato leaf δ 15 N also changed dramatically over the sampling period, indicating a change in N source. The results show a potential for rapid soil recarbonisation with massive application of lignocellulosic biomass in soils, but which is dependent on management. Also, we observed a particular capacity of sweet potato for accessing soil‐bound organic N sources under conditions of high demand.

ABSTRACT Labile organic carbon (LOC) is an important index reflecting soil health, soil organic carbon (SOC) changes and soil productivity. Nevertheless, there are limited studies about the effects of corn straw biochar (CSB) on LOC. Herein, we established an experiment at Mollisols region in northeast China to investigate CSB effects on SOC and LOC fractions of soils and aggregates in different soil layers and periods. The 30 t ha −1 CSB greatly enhanced water content, porosity, the percentages of > 2 and 2–0.25 mm aggregates, and aggregate stability, reduced bulk density, specific gravity and the percentages of 0.25–0.053 mm and < 0.053 mm aggregates. Also, it up‐regulated the contents of SOC, hot water extracted organic carbon (HWC), acid hydrolyzed organic carbon (AHCI and AHCII), and easily oxidised organic carbon (ROC), as well as dissolved organic carbon (DOC) of the 20–40 cm soil layer, of which its contents of HWC, AHCI, AHCII and ROC of > 2 mm aggregates increased by 17%, 31%, 39% and 39%, respectively. SOC and LOC fractions were mainly influenced by water content and porosity. The proportions of HWC and AHCI to SOC and 2–0.25 mm aggregate contribution rate were the highest. Taken together, applying 30 t ha −1 CSB optimally induced the improvement of Mollisols quality by improving physical properties and promoting the percentage and stability of large aggregates to increase SOC and LOC pools.

ABSTRACT Tillage and fertilisation strongly influence nutrient inputs and cycling in agricultural ecosystems. The interrelationships among these nutrients can be effectively described using stoichiometric principles. However, the application of stoichiometric principles to understanding agricultural soil carbon (C) pool dynamics remains underexplored. In this study, we investigated the effects of tillage and fertiliser rate on soil stoichiometry and the C pool through a three‐year field experiment in the North China Plain. Treatments included combinations of no‐tillage (NT) and rotary tillage (RT) with 40% (L), 80% (M), and 100% (H) of conventional fertiliser rate. Results showed that soil stoichiometry generally decreased with increasing soil depth. In 2021, no significant differences were observed among treatments in soil stoichiometry and organic carbon (SOC). However, in 2022, tillage significantly ( p < 0.05) impacted the soil C:N ratio, C:P ratio, dissolved organic carbon (DOC), permanganate oxidizable organic carbon (POXC), SOC, SOC stock, and the carbon pool index (CPI) in 0–10 cm soil depth, with NT outperforming RT by 12.3%, 10.4%, 43.1%, 23.0%, 11.4%, 11.8%, and 11.6%. Fertiliser rate mainly influenced DOC and POXC. Among treatments, the NTM had significantly ( p < 0.05) higher DOC, particulate organic carbon (POC), POXC, SOC, SOC stock, and CPI ranging from 48.7%–83.7%, 19.6%–35.9%, 31.9%–63.3%, 13.9%–23.8%, 18.8%–20.2%, and 19.9%–23.1%, respectively, in 0–10 cm soil depth. Redundancy analyses showed that soil stoichiometry is a key indicator explaining variation in the soil C pool. Partial least squares path modelling further revealed that NTM coordinates the impacts of multiple soil processes and mediates the balance between C and nutrients through stoichiometry, thereby enhancing soil C pool. In conclusion, this study reveals the central role of soil stoichiometry in regulating agricultural soil C pool and highlights the synergistic benefits of combining NTM. These practices support soil health, promote sustainable agricultural development, and contribute to climate change mitigation.