Context Water scarcity poses a significant threat to global food security. Enhancing the compensatory growth capacity of crops following post-drought rewatering is therefore a key strategy for water-efficient agriculture. Aims This study investigates the dual regulatory pathways by which heterotrophic ammonia-oxidizing bacteria (HAOB) influence maize compensatory growth after drought stress. Methods Three functionally distinct strains Y2, Shan2, and C5-3 were selected for co-inoculation experiments. Key results The results show that strain Y2 exhibits strong nitrification ability, Shan2 demonstrates high cytokinin synthesis capacity, and C5-3 possesses both functions. The dual-functional strain C5-3 exhibited the highest biomass at 16.98 g·pot-1 , markedly exceeding both drought and rewatered controls. Co-inoculation of Y2 and Shan2 resulted in a biomass of 16.31 g·pot-1, which was significantly higher than that under single-strain inoculation and comparable to that of C5-3, suggesting a synergistic effect between nitrification and cytokinin-mediated growth promotion pathways. Conclusions HAOB strains exert a dual-function synergistic effect by simultaneously modulating soil nitrogen metabolism and the plant's endogenous cytokinin signaling pathway. Their overall growth-promoting effect surpasses that of strains acting through a single pathway. Implications This study demonstrates that inoculation with HAOB can significantly enhance maize compensatory growth after drought, providing a sustainable microbial strategy to improve water use efficiency and resilience in arid and semi-arid agricultural systems.

Context: Understanding of organic carbon (OC) stock in surface (0-30 cm) and sub-surface (30-60 cm) soils and its determinants are crucial for managing OC in agricultural lands. Aim: Our aim was to examine how land use, soil type, and environmental drivers influence OC stocks in the 0-60 cm soil layers of agricultural regions in New South Wales (NSW), Australia. Method: Soil OC (SOC) and nitrogen (N) stocks were measured across diverse soil types from 50 farms representing pastures and cropping in NSW. The dominant drivers of SOC stocks were identified using random forest (RF) and structural equation modelling (SEM) frameworks. Key results: Overall, cropping and pasture soils carried similar SOC stocks in the 0-60 cm soil layer (80±7 vs 91±7 Mg C ha-1). However, pasture soils had a significantly greater SOC stock in the 0-10 cm soil layer (28±1 Mg C ha-1) than soils from the same layer under cropping (21±2 Mg C ha-1). Ferrosols contained nearly double or greater SOC stock (158±19 Mg C ha-1) in the 0–60 cm soil layer than Vertosols (73±5 Mg C ha-1) and Chromosols (67±6 Mg C ha-1). SOC stocks within different layers decreased with increasing depth at variable rates in different soils. Conclusions: The increased SOC stock in surface soils was mainly driven by climate factors (i.e., precipitation, evapotranspiration), while subsurface SOC stocks depended on more soil properties, i.e., pH, total Fe and Mn contents. Implications: Pasture cultivation in Fe/Al mineral- rich soils may favour SOC building in the surface soil but not in subsurface soil.

Context High-mountain páramos provide essential hydrological services across the Andes. However, green onion cultivation in these ecosystems has led to nitrogen (N) losses, compromising water quality. Aims This study aimed to improve understanding of soil N dynamics in páramo agroecosystems by analyzing the vertical and temporal distribution of total and mineral N in páramo soils, and by developing pedotransfer functions (PTFs) to predict these pools. Method From two cultivated plots and one native grassland plot, 288 soil samples were collected over 7 and 4 months, respectively, at three depths. Samples were analyzed for soil N concentrations, mineral N stocks, and 16 edaphic properties. Using random forest and multiple linear regression (MLR), PTFs were developed incorporating edaphic and remote-sensing covariates. Key results Green onion cultivation altered mineral N distribution, with subsurface nitrate-N reaching 114 mg kg−1, compared to 1.76 mg kg−1 in native grassland. Monthly declines in mineral N stocks reached 75.8 kg N ha−1 in cultivated soils, nearly triple the losses in uncultivated soil. The MLR using edaphic properties performed best for total N and nitrate-N prediction (R2 = 0.80 and 0.64, respectively), while ammonium-N was poorly predicted. Conclusions Shifts in N dynamics were consistent with soil acidity neutralization associated with repeated chicken manure applications, fallow history, and soil texture. These conditions favored subsoil mineral N accumulation, increasing leaching risk. The developed PTFs demonstrate potential to inform site-specific assessments of soil N pools in páramos. Implications Future research should include additional N pools, microbial processes, and isotopic tracers to deepen understanding of N dynamics.

Context Priority Action 1 of the Australian National Soil Action Plan underscores the need for a nationally agreed framework to measure, monitor, map, report, and share information on soil condition and trends. Such a framework supports best-practice soil management, informs evidence-based decision-making, and guides future investments in securing Australia’s soil resources. Aims This study aims to present a statistically robust and operationally feasible sampling design that provides the foundation for a national soil monitoring program. The design seeks to support consistent assessments of soil change, identify emerging threats and opportunities, and enable comparisons between managed and minimally disturbed reference soils. Methods The framework applies a hierarchical, systematic approach to identify representative monitoring sites across Australia’s major agricultural regions. The design centres on the establishment of reference soil areas (Genosoils) for all mapped combinations of soil and landscape types, enabling comparison with managed soils. Flexibility is embedded to accommodate logistical constraints and to integrate legacy datasets and existing monitoring programs where appropriate. Key results The proposed network comprises 4775 sites nationally, of which 3463 fall within agricultural regions. These sites represent 343 unique soil and landscape entities (Pedogenons) and encompass more than 1000 distinct soil and land-use combinations. The framework builds on decades of collaborative, multi-organisational work to develop national soil, landscape, and land-use datasets, which underpin the digital foundation for monitoring. Conclusions The design provides a statistically sound and adaptable foundation for long-term, national-scale soil monitoring in Australia. Its structure enables consistent comparison, integration with existing data resources, and scalability for diverse monitoring objectives. Implications While developed for the Australian context, the approach is broadly transferable. With access to suitable soil and geospatial data, the principles and methodology can be adapted internationally to support comparable monitoring efforts, contributing to global initiatives in soil condition assessment and sustainable land management.

Context Rapid agrarian changes in north-west Cambodia have led to extensive deforestation for upland crop cultivation. Aims This study assessed the impact of four land-use types on soil chemical and biological properties and indicators of soil health. Methods The four land uses were fallow (16 years since forest conversion), maize–cassava (14 years), mango (16 years), and mango–cassava intercropping (15 years). Soil organic carbon (C) and nitrogen (N) stocks, chemical properties, and macro-/meso-fauna were measured at four depths. Soil health indicators were assessed at 0–10 cm: permanganate oxidisable carbon (POXC), aggregation, water infiltration, and visual evaluation of soil structure. Key results Agricultural lands showed lower topsoil C than fallow, with mango–cassava intercropping exhibiting a C depletion rate of −1.42 Mg C ha−1 y−1. Significant N depletion occurred under maize–cassava and mango–cassava (−250 and −260 kg N ha−1 y−1, respectively). Maize–cassava had a higher C/N ratio due to lower N concentrations. Water aggregate stability and POXC were significantly lower under mango–cassava and maize–cassava. Soil fauna abundance and richness were reduced in agricultural lands. Conclusions The forest conversion to agriculture negatively impacted topsoil C (38% loss), labile C (35–70% loss), soil aggregation, and soil fauna. Implications These findings highlight the need to evaluate the costs of soil fertility depletion and explore and promote alternative management practices such as conservation agriculture and agroforestry, alongside financial mechanisms for soil restoration.

Context Biochar has been recommended to improve soil fertility. Biochar may alter the sorptive properties of soil due to its high sorption capacity for organic molecules. However, there is relatively little information in the literature on the medium- and long-term impacts of biochar on soil sorptive capacity based on in situ field experiments. Aims The aim of this study was to evaluate the long-term effect of biochar on atrazine adsorption in field trials. Methods Adsorption isotherms were measured in two field experiments, up to 6 years following a single 16 Mg ha−1 biochar application. Key results Compared to the control, the Freundlich solid–water distribution coefficient was higher in the biochar-amended soils. This effect decreased with time, but remained significantly higher compared with the control treatment up to 5 years after the single biochar application. Conclusions Biochar increased the soil sorption capacity, with a residual effect observable 5 years after a single biochar application. The decrease in sorption capacity of biochar-treated soils over time is likely attributable to the obstruction and/or saturation of biochar sorption sites by clay and indigenous soil organic matter, in addition to pore occlusion. Implications The enhancement of soil sorption capacity with biochar is important for reducing atrazine pollution, a pesticide with high soil mobility and environmental persistence. The biochar’s residual effect indicates its efficacy in regulating the mobility of atrazine. However, the negative effects of increased soil sorption capacity due to biochar must also be considered. Pesticide efficacy may decrease, necessitating higher dosages, while the environmental persistence of organic contaminants could potentially increase.

Context Soil fungi and bacteria play a crucial role in decomposing soil organic matter (SOM) and providing nutrients to terrestrial ecosystems. However, in polar environments, their relative contributions to decomposition remain unclear. Aims This study aimed to determine whether fungi or bacteria contributes more to humic substances (HS) decomposition (the largest constituent of SOM) in maritime Antarctic soils under controlled laboratory conditions with elevated temperature and moisture levels. Methods Soil culturing method was used to select for soil microbes that efficiently degrade HS. During culturing at 18°C for 30 days, Antarctic soils were treated with selective antimicrobials to manipulate microbial communities. After culturing, HS degradation and bacterial communities were analysed. The effects of soil culturing on plant growth were also evaluated using Arabidopsis thaliana as a surrogate for Antarctic plants. Key results HS decomposition and solubilisation were more pronounced in antifungal-treated soils compared to antibacterial-treated soils. Antifungal treatment reduced bacterial alpha diversity, altered bacterial composition, and increased the abundance of rhizosphere-associated Saccharibacteria. Bacterial growth resumed quickly after antibacterial treatment indicating resilience to antimicrobials. Soil culturing resulted in a higher water-soluble HS fraction, which significantly enhanced the fresh and dry weights of A. thaliana. Conclusions Antarctic bacteria exhibit higher degradative activity and resilience to antimicrobials compared to fungi, promoting HS decomposition and solubilisation. This indicates that bacteria have a greater impact on Antarctic soil functioning than fungi. Implications These findings highlight the critical role of bacteria in nutrient cycling and plant growth in polar ecosystems.

Context Precision nitrogen (N) fertilisation, which considers variability in both near-future soil N supply and crop N demand, enables reductions in fertiliser use at the field level, while maintaining high yields and high crude protein (CP) content, and minimising N losses. Aims To determine optimum N fertilisation rates for silage maize (Zea mays) based on variability in soil organic carbon (SOC) and plant available water (PAW) of a 20-ha field, a simulation study using the APSIM model was set up. Methods APSIM was initially tested under Northern European conditions using measurements of biomass, CP and N leaching losses. The model was subsequently applied to determine optimal N rates, taking into account variability in SOC and PAW through different fertilisation scenarios. Model outputs were then used to calculate the required N rates to achieve a target CP of 6.6%, which is the critical value for maximising yield. Key results Compared to a blanket N application across the field, variable N rate application generally increased the proportion of the field achieving the target CP and reduced overall field-scale N leaching. Conclusions Process-based models like APSIM offer a valuable tool for determining optimal N fertilisation rates based on variability in soil properties. However, field testing is essential to validate the effectiveness of this approach under real conditions. Implications The simulations highlight that in sandy soils with high mineralisation potential due to past high organic matter inputs, N fertilisation should be avoided to meet the requirements of given environmental standards for water protection in the European Union.

Context Salinity occurs in sodic soils in Australia, but its effect in Western Australia is poorly understood. Aims We determined the cause of salinity, the ions responsible, and their potential significance as constraints to crop growth on sodic soils at Merredin and Moorine Rock. Methods Soil was collected from 76 profiles to depths of 1.0–1.4 m (388 samples). Samples were analysed for EC1:5, pH, texture, and exchangeable and soluble ions. Results Exchangeable cations were best calculated as the difference between total cations (determined from BaCl2/NH4Cl extracts) and soluble ions (determined from water-soluble extracts). Profiles showed increasing sodicity, alkalinity and salinity with depth. The major soluble cation responsible for salinity was Na+; the major soluble anions were Cl−, HCO3−, SO42−, and CO32−. High salinity in subsoils (depth > 0.2 m) was strongly correlated with dispersive charge (adj. R2 = 0.73). Osmotic potentials were calculated for two levels of gravimetric soil water, the water content of the soils at sampling, or assuming 30% (dry mass basis) soil water. At Moorine Rock, soils mostly had osmotic potentials less than −1.5 MPa. Increasing soil water content to 30% made osmotic potentials less negative. At Merredin, there was strong stratification of osmotic potentials; surface soils mostly had osmotic potentials between 0 and −0.5 MPa, but subsoils mostly had osmotic potentials between −1.0 and −1.5 MPa. Conclusions Crop growth in these landscapes is likely to be constrained by salinity, particularly in dry years.

Context Bletilla sinensis is a perennial orchid herb widely used in Chinese herbal medicine. The endophytic fungi associated with its roots significantly affect plant growth and secondary metabolite accumulation, whereas environmental factors crucially determine the community and diversity of these fungi. Aims This study investigated the impact of habitat environment on the symbiotic relationship between B. sinensis and its endophytic fungi by analysing the community composition and diversity of endophytic fungi in B. sinensis roots at various altitudes. Methods B. sinensis roots were sampled from three altitudes (HXJ1, HXJ2, HXJ3) in Jinjiang Town, Shangri-La County, Yunnan Province, China. Endophytic fungi were isolated and analysed using high-throughput sequencing technology. Key results The endophytic fungi were dominated by Ascomycota (85.4%) and Basidiomycota (14.6%). α-Diversity analysis showed that HXJ2 had the highest species richness (Chao1 = 34), while HXJ1 exhibited the highest diversity (Shannon = 2.25, Simpson = 0.84). β-Diversity analysis revealed moderate community similarities between sampling sites (Bray–Curtis indices: 0.433–0.597). Notably, fungal abundance showed strong positive correlations with soil total phosphorus (r = 1.000, P < 0.01) and total carbon (r = 0.998, P < 0.05) in HXJ1. Conclusions The study revealed a clear altitudinal pattern, where higher altitudes exhibited lower fungal diversity. However, the mid-altitude site (HXJ2) showed higher fungal diversity compared with both higher (HXJ3) and lower altitudes (HXJ1), suggesting that local environmental factors, such as soil nutrients and surrounding vegetation, may interact with temperature to influence fungal diversity. Implications This study sheds light on the symbiotic relationship between B. sinensis and its endophytic fungi, with implications for the cultivation and medicinal properties of this herb.