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Policy and market incentives are rapidly expanding to promote soil organic carbon (SOC) sequestration in global croplands. Evidence suggests that long-term increases in SOC can influence both crop yield and nitrogen (N) fertilizer requirements, with the potential to help address two important sustainability challenges. However, increases in SOC may also trigger higher soil nitrous oxide (N 2 O) emissions, which would represent an important tradeoff for climate change mitigation. We tested the hypothesis that long-term increases in SOC are associated with higher crop yields and fertilizer N use efficiency (NUE), but at the cost of higher N 2 O emissions. Wheat was grown in two soils (SOC low and SOC high) under three N fertilizer rates (0, 100, and 200 kg N ha−1) in a mesocosm experiment. Soils were obtained (0–25 cm) from a 22-yr field experiment on no-till and cover cropping in California. Results indicate that total biomass and grain yield were higher for SOC low than SOC high at 100 kg N ha−1 but not the other N levels. Crop N uptake was also 28% greater for SOC low at 200 kg N ha−1, resulting in higher overall NUE. Soil N 2 O emissions increased for SOC high by 25–112% compared to SOC low , likely due to long-term changes in labile C and N pools, microbial activity, and soil structure influencing porosity and gas diffusion. While there are well-documented crop and environmental benefits from enhancing SOC in agricultural soils, results from this study suggest that changes in soil N 2 O emissions should be considered to accurately determine net GHG emission reductions. • Soil N 2 O emissions increased 25–112% with long-term soil carbon sequestration • Crop yields were not higher with increased SOC • Crop nitrogen uptake and nitrogen use efficiency decreased with increased SOC • Elevated N 2 O emissions presented a tradeoff for net GHG emission reductions [ABSTRACT FROM AUTHOR]

Nitrogen (N) fertilisation is critical for sugarcane crop production. Consequently, overuse of N fertiliser in sugarcane is widespread and it is most prevalent in China. Yet, a comprehensive analysis of sugarcane N balance accounting for different reactive N (Nr) loss pathways, crop N use and soil N retention using 15N labelled fertilisers under commercial high-input cropping conditions is lacking. A two-year field experiment with 5 N levels (0–560 kg N ha−1; N0, N210, N300, N390, N560) was conducted to quantify the effect of N rate on sugarcane yield, Nr loss through different loss pathways, crop N use and soil N retention, and to identify an optimal N rate that sustain high yield whilst reducing Nr loss in Southern China. The results showed that optimal N rate (N300) had similar yield compared with farmer practice (N560) for the plant crop and the ratoon crop. Nitrogen leaching and ammonia loss were increased significantly with increase in N rate, with farmer practice recording the highest Nr loss. Compared with farmer practice, under optimal N application, N leaching was reduced from 211 kg ha−1 to 107 kg ha−1 and from 244 kg ha−1 to 165 kg ha−1 for the plant and ratoon crops, respectively. The ammonia volatilization from the plant crop and the ratoon crop in the optimal N treatment was 24.8 kg ha−1 and 27.0 kg ha−1, respectively, which are considerably less compared with the emission from the farmer practice. There was no significant difference in nitrous oxide emission between optimal N rate and farmer practice. 15N labelling studies showed that crop N recovery, soil N residue and fertiliser N lost at the optimal N rate were 20.9%, 24.9% and 54.2%, respectively, as opposed to 12.5%, 14.8% and 72.7%. respectively, under farmer practice. To the best of our knowledge, this study forms the first comprehensive evaluation of sugarcane N balance accounting Nr loss, N use and native N soil stock covering a wide range of N supply simultaneously in the plant and ratoon crops under commercial crop production condition. This study thus provides very valuable new knowledge not only for crop N supply optimisation in high-input sugarcane production systems as in China but also for sugarcane greenhouse gas accounting studies particularly from climate change mitigation and bioenergy production context. [Display omitted] • First detailed sugarcane crop N balance (Nr loss, N use, soil N stock) estimated. • Current average sugarcane crop N input in China (560 kg N ha−1) very excessive. • Large reduction in N input and Nr loss without yield loss in multi-year field trials. • Leaching, the single largest N loss pathway in sugarcane crop. • Large crop N recovery, fertiliser N loss reduction with optimal N use (300 kg N ha−1). [ABSTRACT FROM AUTHOR]

Cocoa production is a leading driver of deforestation in the humid-tropics of West Africa. Reconciling climate change mitigation with livelihoods of farmers requires identification of production strategies to concurrently improve yield and profit while curtailing emissions of greenhouse gases (GHG). Using a 2021 plot-survey conducted in Ghana's Eastern region, we evaluated yields, GHG emissions, and value of production (VOP) (a profit indicator) across a typology representing the diversity of systems at plot-level. The typology was constructed by first stratifying plots according to shade levels and variety (hybrid vs. Amazonia) which resulted in three systems: Hybrid sun , hybrid variety under full-sun (little to no shade); Hybrid shade , hybrid and moderate shade (13–25 shade trees ha−1); and Amazonia, Amazonia under predominantly moderate shade. Next, factor analysis and clustering were used to group plots within each system according to cocoa yield, vegetation, management, and (local) climate conditions. Cluster analysis showed that fertiliser, weeding, pruning, hand pollination, cocoa tree density, and shade tree densities of differing heights were most influential for determination across systems. Hybrid shade had the highest net GHG removal rate at −6.8 ± 1.7 (± 95% CI) Mg CO 2 eq ha−1 yr−1: 48% and 127% higher (emissions more negative) respectively over Amazonia and Hybrid sun. Hybrid shade additionally had the highest average and least variable VOP among production systems at 669 ± 564 USD ha−1 yr−1, compared to Hybrid sun and Amazonia at 404 ± 442 and 213 ± 280 USD ha−1 yr−1 respectively. These results point to hybrid cocoa grown under moderate shade of 13–25 shade trees ha−1 as optimal for reconciling climate change mitigation with development in West African cocoa. • Study concurrently evaluates financial profits and GHG balances (N 2 O & CH 4 emissions, CO 2 removals) in West African cocoa. • Plot-level indicators are evaluated across a typology obtained from sample-stratification and clustering. • Hybrid cocoa under moderate shade (13-25 shade trees ha-1) had GHG removal increment of 127% over same variety without shade. • This system too had higher mean profits, thus best reconciling GHG mitigation and economic development for the region. [ABSTRACT FROM AUTHOR]

Enhancing biomass yield simultaneously with soil carbon (C) sequestration is a key aim of climate-smart cropping systems. Perennialization is believed to be a suitable mitigation strategy for climate change with the potential for enhancing soil C stocks. Based on a nine-year field experiment in Denmark, we measured the changes in soil C and nitrogen (N) stocks, biomass yield, and yield stability of three perennial (low-fertilized miscanthus, high-fertilized festulolium, and no N-fertilized grass-legume mixture) and two annual (continuous triticale and maize) cropping systems. We found that the changes in topsoil (0–20 cm) and 0–100 cm soil C stocks and topsoil N stocks varied significantly between cropping systems. Over nine years, topsoil C stocks increased by an average of 1.4 Mg C ha−1 in the three perennial cropping systems, while they decreased by 3.4 Mg C ha−1 in the two annual cropping systems. The 0–100 cm soil C stocks increased by 6.8 Mg C ha−1 in the three perennial cropping systems and increased by 2.3 Mg C ha−1 in the triticale system, but decreased by 2.5 Mg C ha−1 in the maize system. Topsoil N stocks increased by 0.18 Mg N ha−1 in three perennial systems while they decreased by 0.08 Mg N ha−1 in the two annual cropping systems. Changes in 0–100 cm soil N stocks did not differ significantly between cropping systems. Miscanthus, festulolium, and maize showed the highest biomass yield (17.1, 16.7, and 16.4 Mg ha−1 year−1, respectively). There were no significant differences among cropping systems in yield stability. This study demonstrated the potential of perennial cropping systems in obtaining higher soil C stocks compared with annual cropping systems while maintaining high biomass yield, supporting perennialization as a promising option for climate-smart agriculture. • Changes in soil carbon (C) and nitrogen (N) stocks under annual and perennial cropping systems were studied over nine years. • Perennial cropping systems significantly increased topsoil C and N stocks compared to annual cropping systems. • Changes in subsoil C and N stocks did not differ significantly between annual and perennial cropping systems. • There was no significant difference in biomass yield and yield stability between annual and perennial cropping systems. [ABSTRACT FROM AUTHOR]

This study investigates the impact of alternative fertilization practices on the yield-scaled global warming potential (YS-GWP) in almond orchards. Almond production is a contributor to greenhouse gas emissions, primarily due to nitrogen-based mineral fertilizers. This research aims to identify strategies that reduce the environmental footprint of almond cultivation while maintaining yield. Field experiments were conducted in an almond orchard using three alternative fertigation practices: Advance Grower Practice (AGP), Pump and Fertilize (P&F), and High Frequency Low Concentration (HFLC). AGP is the current practice used by producers to meet annual N demand for almond tree growth; P&F is a reduction in applied N rate in response to measured N concentrations in the groundwater so that the added N and groundwater N reach the same total N applied; HFLC is a practice of applying smaller N rates per individual event. HFLC uses a greater number of fertigation events to reach similar total annual N load as other treatments. Cumulative N 2 O and CH 4 emissions were used to determine GWP by converting the emissions to carbon dioxide equivalents (CO 2 eq) within a 100-year horizon. Nitrous oxide emissions were multiplied by a radiative forcing potential CO 2 eq of 298 and CH 4 by 25 (UNFCCC, 2007). The results revealed that both P&F and HFLC reduced the YS-GWP compared to AGP. HFLC demonstrated 52–78% decrease in GWP per unit of almond yield compared to AGP, while P&F showed 48–58% decrease over AGP. These reductions were attributed to the reduced nitrous oxide emissions associated with P&F and HFLC. Further, P&F and HFLC tended to have higher N use efficiency than AGP. We demonstrate that adopting alternative fertilization practices can effectively mitigate the environmental footprint of almond orchards while maintaining crop yields. These practices offer viable options for almond growers to reduce greenhouse gas emissions, enhance sustainability, and contribute to climate change mitigation. • Applying nitrogen fertilizer at a lower amount and higher frequency reduces nitrous oxide emissions. • This practice tends to have higher nitrogen use efficiency than standard practice. • It maintains commercial yields at the same level as the standard practice. • It lowers Yield Scaled Global Warming Potential more than the standard practice. [ABSTRACT FROM AUTHOR]

The cultivation of deep-rooted vegetation greatly alters the tradeoffs between water and carbon dynamics, yet their impact on microbial carbon sequestration (MCS) remains inadequately documented, particularly in thick vadose zones. This information is crucial for global climate mitigation and ecosystem service enhancement. As such, we collected triplicate samples for each land use type, exploring the abundance and structure of cbbL -harboring microbial communities within 10-m deep profiles under cultivated farmland and two apple orchards of varying ages (n = 72). Our findings indicated a shift from water-dominated (improved water retention at the expense of reduced carbon sequestration) to carbon-dominated benefits (enhanced carbon sequestration at the expense of decreased water retention) in deep soil layers (2–10 m) after the transformation from farmland to apple orchards. Despite the lack of significant differences among the three land use types, the gene abundances and microbial diversity indices reduced with soil depths because of variations in substrates, resources, and microenvironments. The cbbL -harboring microorganisms consisted of 5 phyla, 7 classes, 19 orders, 30 families, and 55 genera, with Proteobacteria as the predominant bacterial phylum. The relative contributions of different genera varied with soil depths, reflecting their distinct survival strategies. The microbial network was positively connected in various soil layers under farmland and apple orchards. Furthermore, the results of correlation, redundancy analysis, and structural equation modeling jointly indicated that plant roots and soil properties, including total nitrogen and organic carbon, governed MCS processes in deep unsaturated zones. Specifically, the low microbial variation between farmland and apple orchards can be attributed to the predominant effects of climatic and pedogenic factors on soil properties, the restricted contribution of plant roots to soil nutrient levels per unit depth, and the adverse effects of plant-induced ecohydrological consequences on root systems and microbial populations. This study offers new insights within thick vadose zones containing deep-rooted plants, thereby contributing to a better understanding of global terrestrial carbon cycle processes. [Display omitted] • Microbial carbon sequestration processes were explored in 10-m deep profiles. • The farmland-to-apple orchards conversion led to water-carbon tradeoffs. • Microbial carbon sequestration differed with depths rather than land use types. • Depth-dependent plant roots and soil nutrients affects carbon sequestration. [ABSTRACT FROM AUTHOR]

Southeast Asia (SEA) is a key producer and exporter of rice, accounting for around 28% of rice produced globally. To effectively mitigate greenhouse gas (GHG) emissions in SEA rice systems, field methane (CH 4) and nitrous oxide (N 2 O) emissions have been intensively studied. However, an integrated assessment of system-level GHG emissions which includes other carbon (C) balance components, such as soil organic carbon (SOC) or energy use, that can positively or negatively influence the net capacity for climate change mitigation is lacking. We conducted a systematic review of published research in SEA rice systems to synthesize findings across four main components of net system emissions: (1) field GHG emissions, (2) energy inputs, (3) residue utilization beyond the field, and (4) SOC change. The objectives were to highlight effective mitigation opportunities and explore cross-component effects to identify tradeoffs and key knowledge gaps. Field GHG emissions were the largest contributor to net system emissions in agreement with existing scientific consensus, with results showing that practices such as floodwater drainage and residue removal are sound options for CH 4 mitigation. On the other hand, increasing SOC potentially provides a large GHG mitigation opportunity, with long-term continuous rice cropping and practices such as residue incorporation and biochar application promoting SOC increase. A reduction in energy inputs was mainly achieved by optimizing agrochemical use, especially N fertilizers. For residue utilization beyond the field, GHG emission mitigation mainly came from preventing open field burning through residue removal. Removed residue can subsequently be used for producing energy that offsets GHG emissions associated with conventional fuel sources (e.g. fossil fuel-based electricity generation) or substituting material used in other production systems. Integrating all four components of net system emissions into one analysis underscores the following two main takeaways. First, the components of field GHG emissions and SOC change are the biggest opportunities for reducing net system emissions and need to be considered for effective climate change mitigation. Second, the reduction of C inputs through residue removal and increased soil aeration through multiple drainage will lower CH 4 emissions but may also potentially decrease SOC stocks over time. Hence, we argue that future research needs to consider cross-component effects to optimize net system emissions, specifically the "stacking" of best management practices for mitigation related to field GHG emissions or SOC change in long-term experiments. • Net system emissions include field CH 4 /N 2 O emissions, energy inputs, residue utilization, and SOC change. • Integrated review highlights cross-component effects of management including tradeoffs. • Field GHG emissions and SOC change are the largest opportunities for mitigation. • Reduced C inputs and drainage decrease CH 4 emissions, but may negatively affect SOC. • "Stacking" of best management practices is a key knowledge gap that warrants research. [ABSTRACT FROM AUTHOR]

Green manure is a widely applied to increase grain yield, while it also attributes to greenhouse gas (GHG) emissions in agriculture ecosystems. Combining green manure with inorganic fertilizer inputs is a common practice that can influence soil GHG emissions and grain yield, however, its impacts on grain yield and global warming potential (GWP) under different initial soil conditions before rotating experiments and agronomic management in paddy fields remain unclear. We synthesized 508 data pairs to evaluate the responses of CO 2 emissions, CH 4 emissions, N 2 O emissions, and grain yield to combined inputs of green manure plus inorganic fertilizer compared with only inorganic fertilizer application. Our findings indicate that both inorganic fertilizer plus extra green manure (GM-E) and green manure substitutes for inorganic fertilizer (GM-S) could increase CO 2 emissions (22.5 %−76.8 %), CH 4 emissions (100 %−103 %), N 2 O emissions (29.8 %−50.9 %), and yield (2.21 %−19.6 %). Except for GM-E, which showed a non-significant increase in grain yield. The initial soil properties before rotating experiments, the types and timing of green manure application were key drivers of GHG emissions and yield, and extra green manure applied in areas with low initial soil pH and high C:N can increase GWP and yield. Overall, the mixed green manure application had greater impact than leguminous or non-leguminous green manure applied alone. The responses of GHG emissions and yield to GM-S were modulated by mean annual precipitation and initial soil properties before rotating experiments, and green manure substitutes for inorganic fertilizer in areas with high initial soil pH and low C:N can increase GWP and yield. Meanwhile, excessive precipitation caused a reduction in yield and a significant increase in GWP intensity. Our results showed that extra green manure applications of less than 68.1 kg N ha−1 would not significantly increase GWP. Therefore, an effective green manure strategy can achieve a win-win situation for the dual challenge of agricultural production and climate change mitigation. • Green manure inputs significantly increased GHG emissions from paddy fields. • Green manure combined inorganic fertilizer may not increase the yield significantly. • Mixed green manure had greater impact than single-type green manure application. • Green manure substitutes for inorganic fertilizer may not increase the GWPI. • Extra green manure (<68.1 kg N ha-1) is recommended to achieve a win-win situation. [ABSTRACT FROM AUTHOR]