Barren paddy fields characterized by poor soil structure, shallow tillage layers and low organic carbon content are a common limitation to rice production in subtropical China.  As a novel approach to soil improvement, granulated organic amendments offer significant potential.  Previous studies have shown that granulated straw can improve soil physicochemical properties and rapidly increase the soil organic carbon (SOC) content.  However, their effects on barren paddies remain underexplored.  This study evaluated four soil amendment strategies: no organic amendments (CK), 10 t ha^–1 of composted manure (M10), 20 t ha^–1 of granulated organic amendment (G20), and 40 t ha^–1 of granulated organic amendment (G40).  The objective was to assess the effects of these amendments on soil structure, the contents of aggregate-associated carbon (AAC), particulate organic carbon (POC) and mineral-associated organic carbon (MAOC), and the chemical stability of MAOC among various size aggregates in both topsoil (0–20 cm) and subsoil (20–40 cm).  The results demonstrated that organic amendment inputs significantly increased the macroaggregate (>250 µm) proportion and improved soil structural stability.  These amendments also elevated the carbon concentration within aggregates of various sizes and facilitated the redistribution of organic carbon from microaggregates (53–250 µm) and silt+clay fractions (<53 µm) to macroaggregates.  The proportion of POC to AAC declined with decreasing aggregate size, whereas the proportion of MAOC increased.  In the topsoil, macroaggregate formation enhanced the protection of POC, supported the accumulation of non-hydrolyzable carbon within MAOC, and accelerated the formation of intra-microaggregates.  In the subsoil, mineral-bound organic carbon remained the dominant form of carbon sequestration.  In conclusion, the application of 40 t ha^–1 of granulated organic amendment proved to be a successful tactic for enhancing soil physicochemical structure, increasing SOC content, and improving carbon stability.  This approach offers a promising and innovative solution for the sustainable management and restoration of barren paddy fields.  

Microorganisms carrying cbbL, pmoA and coxL genes play crucial roles in regulating soil-atmosphere exchanges of carbon trace gases (CO₂, CH₄, and CO).  However, the geographical distribution patterns of these functional genes in agricultural ecosystems and their environmental drivers remain poorly understood.  Here, we surveyed agricultural soils across four climate zones (tropical, subtropical, warm temperate, and mid-temperate) in eastern China to quantify the abundances of CO₂-assimilating bacteria (cbbL gene), methanotrophs (pmoA gene), and CO-oxidizing bacteria (coxL gene).  We found significant ecosystem-specific patterns: the cbbL gene was more abundant in upland soils (averaging 9.46×10⁹ copies g^–1) than in paddy soils (6.44×10⁹ copies g^–1).  In contrast, methanotrophs abundance was 1 to 3 orders of magnitude higher in paddy (averaging 1.17×10⁸ copies g^–1) than in upland (5.78×10⁶ copies g^–1) soils.  The coxL gene maintained similar abundance levels across both soil types (averaging 6.12×10⁸ vs. 5.91×10⁸ copies g^–1).  Structural equation models revealed that spatial factors primarily shaped cbbL and pmoA in uplands, whereas total bacterial abundance was the dominant predictor for all three genes in paddy soils.  These results highlight distinct ecological controls on microbial functional groups and provide a predictive framework for how land use and climate change may regulate microbial mediation of carbon gas fluxes across a continental-scale transect in eastern China.

Rapidly improving infertile croplands and enhancing their soil organic carbon (SOC) pool necessitate substantial organic materials incorporation.  Converting loose crop straw into granulated form facilitates uniform incorporation within the plough soil layer.  As an innovative soil amelioration approach, the efficiency and patterns of SOC accumulation remain unclear.  Two field experiments were conducted in infertile subtropical upland and paddy soils with 0, 30, 60, and 90 Mg ha⁻¹ granulated straw incorporation.  After one year, SOC accumulation efficiency from straw input remained stable in upland (30.8–37.5%) with increasing amounts of straw incorporation, while declined from 60.0 to 38.3% in paddy.  In both croplands, the contributions of lignin phenols to SOC increased with increasing straw incorporation, while the contributions from amino sugars remained constant at higher straw input levels.  Subsequently, the ratios of lignin phenols to amino sugars increased with increasing straw incorporation, indicating faster plant residue accumulation compared to microbial necromass, as the granulation approach limited microbial involvement in straw transformation.  Thus, single-time incorporation of substantial granulated straw presents an effective agricultural strategy for rapid amelioration of infertile croplands.

The United Nations Sustainable Development Goal (SDG) 2 aims to achieve Zero Hunger by 2030.  However, global hunger and food insecurity have continued to rise at an alarming rate (UN 2023).  Subtropical regions are home to more than 30% of the world’s population, predominantly in developing countries where per capita farmland and food supply are only 40% of those in developed nations (FAO 2018).  Meeting the Zero Hunger target amid ongoing population growth in these regions requires a substantial increase in agricultural production while minimizing soil degradation and adverse ecological impacts.  This challenge is shared by many countries across South Asia, Africa, and Central and South America.

Against this background, the 4th International Symposium on Sustainable Agriculture for Subtropical Regions (ISSASR-4) was held from June 21 to 24, 2024, in Changsha, China, hosted by the Institute of Subtropical Agriculture, Chinese Academy of Sciences.  The symposium brought together over 300 experts and scholars from nearly 30 countries.  Under the theme “Ecosystem Management and Agricultural Green Development in Subtropical Regions”, discussions focused on four key topics: (i) regional resources and ecosystem management for enhancing agricultural productivity, (ii) green crop and animal production, (iii) minimizing adverse environmental impacts of agricultural production, and (iv) the growing role of big data, artificial intelligence (AI), and smart farming.  Participants exchanged the latest research advances, identified major challenges, and explored countermeasures for agriculture and ecological sustainability in subtropical regions worldwide.

This Special Focus of the Journal of Integrative Agriculture (JIA) addresses these pressing issues by presenting empirical evidence and innovative solutions for agricultural green development.  It comprises 13 papers covering a wide range of topics related to carbon, nitrogen, and phosphorus pathways in natural and agricultural ecosystems, with attention to microbial processes, land-use change, production management, and their effects on nutrient cycling and grain yield.  We hope this collection enhances understanding of ecosystem management and green agricultural development, offering actionable insights for policymakers, researchers, and practitioners.

Section 1: Regional resources and ecosystem management

This section examines three key areas: agricultural bio-resources, soil carbon and nutrient dynamics across ecosystems, and regional grain supply–demand matching.  Studies provide insights into bioinput-based agricultural frameworks, soil nutrient responses to climate change and anthropogenic influences, and the dynamic, heterogeneous patterns of grain matching.  Vermelho et al. (2026) reviewed microbial bioinputs, outlining their categories, mechanisms, global challenges, and Brazil’s production infrastructure and regulatory context.  Wang M M et al. (2026) reported moderate spatial variation with positive autocorrelation in soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP), and total potassium (TK), noting greater vulnerability to phosphorus and potassium limitation than to nitrogen, with soil properties outweighing spatial or environmental factors in explaining nutrient variation.  Another study by Wang L Y et al. (2026) identified climate and hydrological changes as key drivers of SOC loss in Dongting Lake, with accelerated loss occurring above 21.4 m elevation, suggesting that managed water levels during droughts could enhance carbon sequestration.  Wan et al. (2026) showed that plantations can mitigate climate change by increasing carbon storage at the aggregate scale in alpine regions.  Miao et al. (2026) demonstrated a scale-dependent mismatch in grain supply and demand, highlighting how interregional flows from 1980 to 2020 reduced deficit areas.  Together, these studies advance frameworks for sustainable ecosystem management.

Section 2: Green crop production in subtropical regions

Enhancing green crop production in subtropical regions requires practices that improve soil health and carbon sequestration while sustaining yields.  Given the vulnerability of subtropical croplands, effective strategies for maintaining SOC are critical.  Hua et al. (2026) found that long-term livestock manure substitution improves soil aggregate stability and reduces water erosion but increases lateral loss of labile organic carbon, revealing a trade-off.  Kautsar et al. (2026) reported that terrace reconstruction altered rice yields between field sides and modified SOC, TN, and decomposition dynamics in the 15–30 cm layer, with subsoil fertility determining productivity.  Wang J et al. (2026) demonstrated that massive granulated straw incorporation boosts SOC and crop yield in infertile soils, with accumulation efficiency ranging from 30.8 to 60.0%, primarily from plant residues.  These studies highlight practical pathways for sustainable soil management.

Section 3: Environmental impacts of agricultural production

Assessing and mitigating agriculture’s environmental footprint requires a multiscale understanding of soil ecological processes.  Pan et al. (2026) found that natural restoration enhances karst soil phosphorus-cycle multifunctionality more than artificial restoration or cropping, driven by increased SOC and bacterial network complexity, with rare phoD-harboring taxa playing a critical role.  Wang Y et al. (2026) reported that niche outweighs genotype in shaping pea fungal communities, with β-diversity driven by species replacement and deterministic assembly in niche-based groups.  Zhu et al. (2026) showed that SOC is higher in brown and yellow-brown soils and that spring irrigation significantly increases farmland SOC, supporting carbon sequestration.  Zheng et al. (2026) demonstrated that spatial factors govern carbon-cycling gene abundances in uplands, while biotic and substrate factors dominate in paddy soils, revealing an integrated “microbial carbon pump” in trace-gas cycling at a continental scale.  Collectively, these studies advance understanding of the mechanisms underlying soil functionality and greenhouse gas modulation.

Section 4: Big data, artificial intelligence and smart farming in agriculture

The integration of big data, AI, and smart technologies is pivotal for the digital transformation of agriculture.  This section presents a study on their practical application to environmental challenges.  Wang M H et al. (2026) developed an Android-based decision support system (CNPDSS) to control non-point source nitrogen (N) and phosphorus (P) pollution.  Integrating GIS, a Bayesian predictive model, an optimization algorithm, and a smartphone interface, the system identified solutions that minimize both pollutant loadings and engineering costs in the Tuojia catchment, China.  Its adaptive design demonstrates potential for broader application, offering a scalable tool for sustainable water quality management.

This Special Focus underscores the critical intersection of ecosystem management and agricultural development in subtropical regions.  Through 13 studies organized across four themes - resource management, green production, environmental impact mitigation, and smart technology - the collection provides a science-based framework for enhancing productivity while preserving ecological integrity.  It offers concrete insights for achieving sustainable food systems and advancing the UN Zero Hunger goal in some of the world’s most vulnerable and vital agricultural landscapes.

Straw amendments can improve soil fertility by loading organic carbon (C) into soils, but whether and how biological nitrogen fixation (BNF) occurs in long-term rice straw (RS)-incorporated paddy fields remain poorly understood. To fill this gap, we explored the effects of three rates of straw incorporation (0, 3 and 6 t ha^-1; RS₀, RS₃ and RS₆) on soil BNF activities inferred from acetylene reduction assay (ARA) and diazotrophic communities at three rice growth stages (tillering, elongation, and maturation) based on a 10-year field experiment. The ARA activities increased significantly in response to increasing straw incorporation rates across all three rice growth stages, while the effect decreased as rice growth progressed. Soil BNF was associated with key diazotrophs, such as Dechloromonas, Bradyrhizobium, and Azospirillum. Straw incorporation increased diazotrophic abundance, diversity and interactions, which consequently improved soil BNF activities and rice yields. Straw incorporation increased rice yield by 12.6% in RS₃ and by 15.5% in RS₆ compared with the control. Structural equation models (SEMs) suggested that microbial C turnover and nitrogenase gene expression were the key factors affecting soil stage-specific BNF associated with the decomposition of straw. These results revealed that C-rich straw incorporation reconfigured soil N dynamics, enabling simultaneous improvement of soil fertility and rice yields through demand-driven BNF patterns in paddy fields.