Spatial patterns of net greenhouse gas balance and intensity in Chinese orchard system

Carbon emissions peak of China's apple cultivation achieved in 2014: a comprehensive analysis and implications

Carbon sequestration and emission reduction in apple cultivation are of great significance for achieving sustainable agricultural development and combating climate change. However, the status of carbon emissions from apple cultivation is unclear, and this study will provide implications for the agriculture sector. This study applied the life cycle assessment method to quantify carbon emissions and analysed the footprint composition of apple orchards in China, and identified the emissions peak based on the Mann-Kendall analysis. The results showed that the carbon emissions of apple cultivation reached the carbon peak in 2014. The carbon emissions per unit area (CEA) and per unit yield (CEY) were 5.79 t CO2eq ha-1 and 0.23 kg CO2eq kg-1 in 2021, respectively. Carbon emissions from fertilizers (54.4%) and irrigation electricity (30.9%) were identified as the dominant components in apple orchards. Specifically, Henan and Shandong exhibited higher growing advantages, characterized by higher carbon economic efficiency and lower CEY. The carbon emissions of the ideal scenario will be decreased 69.6% through optimizing fertilizers and energy restructuring. In conclusion, promoting low-carbon development in apple orchards can be achieved through targeted in-field mitigation measures, such as optimizing the amount and types of fertilizers, and adopting new energy for agricultural machinery.

Comparison between tropical legumes and natural grasses in improving tropical rainforest soil health: a case study in guava (Psidium Guajava L.) orchards

Tropical rainforest soils, or latosols, are distinguished by their low pH and low fertility. In orchards, co-cultivating grass has become popular as a way to improve soil quality and boost fruit production. Nevertheless, insufficient information is currently available about the response of soil microbial communities in tropical rainforest orchards to grass co-cultivation. Therefore, the present research investigates the effect of grass cultivation on the soil properties and microbial diversity of guava (Psidium guajava L. cv Pearl) latosol orchards. Two varieties of the tropical legume grass Stylosanthes guianensis, i.e., Reyan No. 2 and Ubon, were studied, besides the control (CK), which is without any grass, and the natural grasses treatment (N). The study contained four treatments, i.e., S. guianensis cv. Reyan No. 2, S. guianensis cv. Ubon, CK, and N. Soil samples from the top layer (0-20 cm) and subsoil layer (20-40 cm) were collected to follow the changes in soil microbial biodiversity based on 16 S rDNA analysis. A total of 17,231 kinds of OTUs (Operational Taxonomic Units) were obtained, including 17,165 kinds of bacteria and 66 kinds of Archaea. S. guianensis cv. The Ubon variety, natural grasses, and CK treatments significantly increased the soil microbial richness and evenness in the topsoil layer compared to Reyan No. 2 variety. The β-diversity of soil microbial community was significantly reduced in the natural grasses and Ubon variety treatments at the topsoil layer compared to CK treatment. In the subsoil layer, natural grasses, Reyan No. 2, and Ubon treatments significantly increased the soil microbial community based on β-diversity. The presence of natural grasses caused 49% and 42% increases in the SOC in the top and subsoil layers, respectively, as well as remarkable increases in the available and total soil nitrogen. The grass intercropping enhanced the levels of soil carbon and nitrogen and altered the nature of the soil's microbial community. The diversity of soil microorganisms in the subsoil layer is significantly altered by the shallow root systems of tropical legume and natural grasses, which have most of their roots concentrated in the top soil layer. Overall, growing grass in tropical orchards benefits the latosolic soil microorganisms, which has enhanced the theoretical underpinnings for using grass to improve the soil quality in latosols orchards.

Ground cover management enhances soil extracellular enzyme activities across Chinese orchards

The impacts of ground cover management (GCM) on orchard soil properties have been extensively studied. However, the quantitative assessment of soil extracellular enzyme activities (EEAs) in mulch agriculture remains understudied. In this study, we investigated EEAs related to GCM to assess microbial metabolic activity, soil health, and nutrient status, based on 81 studies focusing on orchards in China. Our findings show that GCM significantly increases carbon acquisition (C-acq, 37%), nitrogen acquisition (N-acq, 34%), phosphorus acquisition (P-acq, 26%), and oxidative decomposition (OX, 14%) enzymes compared to continuous clean tillage. A subgroup analysis and a random forest model were conducted to further identify the effects and potential mechanisms through which soil EEAs respond to GCM in orchards under various moderators. The significant changes in EEAs induced by GCM vary with experimental and environmental factors. Tree age, climate conditions, and soil depth are the primary contributors to the variation in soil EEAs. Overall, our results suggest that the implementation of GCM positively affects EEAs, thereby enhancing microbe-mediated soil ecosystem functions and soil fertility. This meta-analysis provides comprehensive evidence of GCM-induced effects on hydrolase and oxidase activity, improving our understanding of the underlying mechanisms by which orchard mulching impacts soil nutrient cycling.

Carbon budget of diversified cropping systems in southwestern China: Revealing key crop categories and influencing factors under different classifications

Cropping systems are considered the largest source of agricultural GHG emissions. Identifying key categories and factors affecting cropping systems is essential for reducing these emissions. Most studies have focused on the carbon budget of cropping systems from the perspective of a single crop or crop category. Comprehensive studies quantifying the carbon budget of diversified cropping systems, including farmland and garden crops, are still limited. This study aims to fill this gap by quantifying the carbon budget of diversified cropping systems, clarifying their carbon attributes, and identifying key crop categories and influencing factors within different classifications of the system. This study analyzed the carbon budget of a diversified cropping system consisting of 19 crops in Yunnan Province, southwestern China, using a crop-based net greenhouse gas balance methodology based on the "cradle-to-farm" life cycle idea. Crops were categorized into three levels of categories to assess the potential impact of categorization within the cropping system on its carbon balance. Results showed that Yunnan's diversified cropping system is a significant carbon sink, with net sequestration of 33.1 Mt CO2 eq, total emissions of 37.4 Mt CO2 eq, and total sequestration of 70.5 Mt CO2 eq. Cereals, vegetables, and hobby crops were the main contributors to carbon emissions, accounting for 41.61%, 21.87%, and 15.37%, respectively. Cereal crops also made the largest contribution to carbon sequestration at 53.18%. Bananas had the highest emissions per unit area (11.45 t CO2 eq ha-1), while walnuts had the highest sequestration (20.64 t CO2 eq ha-1). In addition, this study highlights effective strategies to reduce greenhouse gas emissions, such as reducing nitrogen fertilizer use, minimizing reactive nitrogen losses, and controlling methane emissions from rice fields. By elucidating the impact of carbon dynamics and crop categories, this study provides insights for sustainable agricultural practices and policies.

Living grass mulching improves soil enzyme activities through enhanced available nutrients in citrus orchards in subtropical China

Living grass mulching (LGM) is an important orchard floor management that has been applied worldwide. Although LGM can effectively enhance soil nutrient availability and fertility, its effects on microbial-mediated soil nutrient cycling and main drivers are unclear. Meanwhile, the variation of enzyme activities and soil nutrient availability with LGM duration have been rarely studied. This study aims to explore the effects of mulching age and soil layer on enzyme activities and soil nutrients in citrus orchards. In this study, three LGM (Vicia villosa) treatments were applied, i.e., mulching for eight years, mulching for four years, and no mulching (clean tillage). Their effects on the enzyme activities and soil nutrients were analyzed in different soil layers of citrus orchards in subtropical China, i.e., 0-10, 10-20, and 20-40 cm. Compared to clean tillage, mulching for four years had fewer effects on enzyme activities and soil nutrients. In contrast, mulching for eight years significantly increased available nitrogen (N), phosphorus (P) nutrients, β-glucosidase, and cellobiohydrolase activities in the soil layer of 0-20 cm. In the soil layer of 0-40 cm, microbial biomass carbon (C), N, P, N-acetylglucosaminidase, leucine aminopeptidase, and acid phosphatase activities also increased (P < 0.05). Mulching for eight years significantly promoted C, N, and P-cycling enzyme activities and total enzyme activities by 2.45-6.07, 9.29-54.42, 4.42-7.11, and 5.32-14.91 times, respectively. Redundancy analysis shows that mulching treatments for eight and four years had soil layer-dependent positive effects on soil enzyme activities. Microbial C and P showed the most significant positive correlation with enzyme activities, followed by moisture content, organic C, and available N (P < 0.05). Available nutrients contributed almost 70% to affect enzyme activities significantly and were the main drivers of the enzyme activity variation. In summary, LGM could improve soil enzyme activities by increasing available nutrients. The promotion effect was more significant under mulching for eight years. Therefore, extending mulching age and improving nutrient availability are effective development strategies for sustainable soil management in orchard systems. Our study can provide valuable guidelines for the design and implementation of more sustainable management practices in citrus orchards.

Factors shaping soil organic carbon stocks in grass covered orchards across China: A meta-analysis

Orchard grass coverage has been widely adopted to increase fruit yield by improving soil fertility. However, the impact of the environment on the changes in soil organic carbon (SOC) stocks consecutive to orchard grass coverage remain poorly quantified at a large scale. The present study aimed to examine the responses of SOC stocks to grass coverage at a soil depth of 0-30 cm in orchards compared to clean tillage. A total of 342 observations across China from 139 peer-reviewed publications were subjected to meta-analysis. Aggregated boosted tree analysis was performed, evaluating the determinants of SOC stocks, such as plant traits (e.g., fruit tree type, grass type, orchard age, and grass age), edaphic variables (e.g., initial SOC and nitrogen concentration, soil pH, and soil clay content), climatic factors (e.g., mean annual precipitation (MAP) and mean annual temperature (MAT)), and management practices (e.g., grass source, grass growing mode, fertilization, grass mowing, placement of mowed residues, and irrigation). On average, orchard grass coverage significantly enhanced SOC stocks by 21.47% (percentage change) compared to clean tillage. Biotic and abiotic factors influenced this increase in SOC stocks following grass coverage in orchards to different extents. Grass age and soil clay content were the main determinants driving the variation in the SOC stocks following grass coverage in orchards. Thus, we propose an efficient way to optimize C sequestration in grass covered orchards, regarding plant traits, climatic factors, edaphic variables, and management practices. Longer than 12 months of surface grass coverage with cultivated grass species in mature deciduous fruit orchards (≥5 years) efficiently increased SOC stocks. This is particularly the case for acidic (pH < 6.5) soils with low C content (SOM < 15 g kg^-1) in areas with suitable rainfall and temperature conditions (MAP ≥ 400 mm, MAT ≥ 10 °C). Collectively, this meta-analysis identified orchard grass coverage as a promising practice for significantly increasing SOC stocks at 0-30 cm across large geospatial locations in China.