Croplands In China Research Articles

Green Agriculture: An Assessment of the Effectiveness of Centralized Management of Contaminated Cropland in China

Green Agriculture: An Assessment of the Effectiveness of Centralized Management of Contaminated Cropland in China

Assessing the bioenergy potential of abandoned cropland in China: Toward an optimal distribution of bioenergy crops

Bioenergy has gained wide attention due to its potential to reduce fossil fuel consumption and greenhouse gas emissions. Abandoned cropland is a promising option for cultivating bioenergy crops, as it does not compete with food production. The vast amount of abandoned cropland in China provides extensive opportunities for the development of bioenergy. However, the bioenergy potential of China's abandoned cropland remains unclear. In this study, we identified abandoned cropland in China for the period of 2000–2020. Based on this, we estimated the bioenergy potential from conventional food crops (maize and wheat), and perennial bioenergy crops (miscanthus and switchgrass), on the abandoned cropland in China. We optimized the planting of conventional food and two perennial bioenergy crops by maximizing crop yield and accounting for water limits. The results show that 29.49 Mha of abandoned cropland was found in the past twenty years. Spatially, it was mainly located in eastern China with relatively high soil quality, in contrast to that in the U.S. and Europe. By optimizing the crop distribution on abandoned cropland, the bioenergy potential primarily shows a spatial distribution of higher potential in the south and lower potential in the north, with a total yield reaching 9.52 EJ. This is approximately 1.43 times higher than that of solely cultivating miscanthus and 8.28 times that of wheat. This potential accounts for 6 % of China's total primary energy consumption in 2022 and 7.66 % of the carbon emission peak target for 2030. It holds significant importance for the national emission reduction strategy. These findings highlight the immense bioenergy potential of abandoned cropland, providing support for the development of bioenergy.

Prediction of soil organic matter using Landsat 8 data and machine learning algorithms in typical karst cropland in China

Soil organic matter (SOM) is crucial for karst ecosystems, affecting cropland health, climate change mitigation, and rocky desertification control. However, there are limited research on cropland SOM prediction in karst areas with complex topography and diverse microclimates. Here, we compared the performance of four machine learning algorithms—random forest (RF), support vector regression (SVR), multilayer perceptron regression (MLP), and gradient boosting regression trees (GBRT)—for predicting cropland SOM in a typical karst landform area in 2019. Our results indicated that the GBRT model achieved the highest prediction accuracy with an R² of 0.69, MAE of 2.19 g/kg, RMSE of 3.37 g/kg, and LCCC of 0.82. Using the GBRT model and spatial data on climate, topography, and remote sensing, we predicted SOM for each 30 m × 30 m grid cell. The analysis revealed higher SOM content in the northeastern and southwestern regions and lower content in the central area, ranging from 13.95 to 47.81 g/kg, with an average of 27.16 g/kg. Lime soil had the highest SOM content, while purple soil had the lowest. Paddy fields showed significantly higher SOM than dry land. Over the past 40 years, SOM content has slightly increased, while its spatial distribution has remained stable.

Spatiotemporal Distribution and Driving Mechanisms of Cropland Long-Term Stability in China from 1990 to 2018

Long-term stability is crucial in cropland for maintaining stable agricultural production and ensuring national food security. However, relatively few studies have been conducted on the long-term stability of cropland at the national level. This study assessed the long-term stability of cropland in China from 1990 to 2018 using a fine-resolution land use dataset. The experimental results indicated that the average area of unstable cropland in China from 1990 to 2018 amounted to 2.08 × 106 km2, 47.31% of the total. The Qinghai–Tibet Plateau exhibited the highest average proportion of unstable cropland at 65.9%, followed by the northern arid and semiarid region, Southern China, and the Yunnan–Guizhou Plateau. The quantity of unstable cropland in China initially declined before increasing, reaching a final growth rate of 5.09%. Furthermore, this study explored the relevant driving factors of cropland’s long-term stability from both natural factors and human activities based on artificial neural networks. The relative importance of distance to vegetation reached a value of 0.30, indicating that it had the most significant influence on the long-term stability of cropland, followed by relief amplitude and soil type. This phenomenon may be attributed to the inadequate execution of the Grain for Green Policy and the requisition–compensation balance of cropland policy, along with the depletion of young and middle-aged laborers due to urban migration from rural areas. Local governments should focus on addressing the unsustainable exploitation of sloped land in rural mountainous or hilly regions while preventing urban developers from appropriating fertile cropland to compensate for less fertile areas.

Divergent effects of long-term fertilization on the carbon management index across soil profiles in key Chinese croplands

Evidence for the variability of the carbon (C) management index (CMI) across surface and subsurface soil layers due to long-term fertilization in diverse agroecological settings is inadequate. Thus, our study aimed to explore the variations in soil organic C (SOC), CMI, and its response ratio (RR-CMI) along soil profiles (0–60 cm) across four croplands in China. These croplands represented two high-fertility sites in Gongzhuling (GZL) and Chongqing (CQ) and two low-fertility sites in Zhengzhou (ZZ) and Qiyang (QY). We evaluated various treatments: control (CK; no fertilizer), inorganic fertilizer (NPK), NPK combined with standard manure (MNPK), and 1.5 times the standard rate of manure and NPK (1.5MNPK). The results indicated a significant increase in SOC content across all depths, ranking as 1.5MNPK > MNPK > NPK > CK, with ranking for the pattern observed across sites as GZL > CQ ≈ QY > ZZ. This led to the most substantial increases, reaching 107, 86, 105, and 62 % more than CK across the soil profile (0–60 cm) under 1.5MNPK across all sites. Moreover, the same treatment showed a significantly higher CMI at 0–60 cm compared to CK, with increases of 37, 19, 65, and 25 % for ZZ, QY, GZL, and QY, respectively. Notably, for the low-fertility soils (ZZ and QY), a higher CMI was observed in the 0–20-cm soil layer), whereas the opposite was true for the high-fertility soil (GZL). Consequently, low-fertility soils exhibited a higher RR-CMI in the 0–20-cm soil layer, whereas the high fertility site (GZL) showed a higher RR-CMI in the 40–60-cm soil layer, suggesting differential accumulation and loss of SOC regulated by soil depth and inherent site fertility. Partial least squares regression analysis further indicated that soil and climatic factors predominantly influenced CMI under long-term fertilization in typical Chinese soils. In conclusion, the long-term application of manure combined with inorganic fertilizer promotes SOC sequestration and enhances CMI, presenting a viable management strategy for enhancing soil quality in the studied regions.

Effects of diffuse light on the gross ecosystem primary productivity of a winter wheat (Triticum aestivum L.) cropland in northern China

Diffuse light is produced by clouds and aerosols in the atmosphere. Exploring the effects of diffuse light on ecosystem productivity is important for understanding the terrestrial carbon (CO2) cycle. Here, 2 years of gross ecosystem primary productivity (GEP) from a (winter) wheat cropland in China was assessed using eddy covariance technology to explore the effects of diffuse photosynthetic active radiance (PAR) on wheat GEP. Wheat GEP increased significantly and positively along with diffuse PAR. In addition, wheat GEP was significantly affected by total PAR, air temperature, and vapor press deficit in different diffuse PAR fraction (fDIF) change stages. Because significant autocorrelations existed among the controlling factors, a path analysis was used to quantify the effects of diffuse light on GEP. Diffuse PAR was the primary and secondary importance factors affecting GEP with direct path coefficients of 0.54 and 0.48, respectively, in different fDIF change stages. A multilayer canopy model revealed that the middle and lower canopy levels intercepted more light when diffuse PAR increased. This resulted in the photosynthetic enhancement of middle and lower canopy levels, which contributed approximately 65% and 35%, respectively, to the increase in photosynthesis for the entire canopy (~ 30.5%). Overall, our study provided new evidence regarding the importance of diffuse light for CO2 uptake in agroecosystems, which is important for predicting the responses of ecosystem CO2 budgets to future climate-related light changes.

Increased straw return promoted soil organic carbon accumulation in China's croplands over the past 40 years

Quantifying changes in soil organic carbon (SOC) stocks within croplands across a broad spatiotemporal scale in response to anthropogenic and environmental factors offers valuable insights for sustainable agriculture aimed to improve soil health. Using a validated and widely used soil carbon model RothC, we simulated the SOC dynamics across intensive croplands in China that support ∼22 % of the global population using only 7 % of the global cropland area. The modelling results demonstrate that the optimized RothC effectively captures SOC dynamics measured across 29 long-term field trials during 40 years. Between 1980 and 2020, the average SOC at the top 30 cm in croplands increased from 40 Mg C ha−1 to 49 Mg C ha−1, resulting in a national carbon sequestration of 1100 Tg C, with an average carbon sequestration rate of 27 Tg C yr−1. The annual increase rate of SOC (relative to the SOC stock of the previous year), starting at <0.2 % yr−1 in the 1980s, reached around 0.4 % yr−1 in the 1990s and further rose to about 0.8 % yr−1 in the 2000s and 2010s. Notably, the eastern and southern regions, comprising about 40 % of the croplands, contributed about two-thirds of the national SOC gain. In northeast China, SOC slightly decreased from 58 Mg C ha−1 in 1980 to 57 Mg C ha−1 in 2020, resulting in a total decline of 28 Tg C. Increased organic C inputs, particularly from the straw return, was the crucial factor in SOC increase. Future strategies should focus on region-specific optimization of straw management. Specifically, in northeast China, increasing the proportion of straw returned to fields can prevent further SOC decline. In regions with SOC increase, such as the eastern and southern regions, diversified straw utilization (e.g., bioenergy production), could further mitigate greenhouse gas emissions.

The different vegetation types responses to potential evapotranspiration and precipitation in China

Global climate change is considered one of the greatest environmental threats in the world. It is expected to significantly change the global hydrological cycle. The two main water cycle components, potential evapotranspiration (PET) and precipitation (P), are closely related to vegetation dynamics. In this study, the partial correlation analysis method was used to analyzed the relationship between Normalized Difference Vegetation Index (NDVI) and climate factors (PET and P) based on grid cells. PET was calculated by FAO-56 Penman–Monteith method. Moreover, we also investigated the NDVI and climate factors in different vegetation cover types. The results showed that grassland, forest and cropland in China were positively correlated with PET and P. The time scales of the maximum partial correlation coefficients between NDVI and PET of grassland vegetation were mostly longer than 5–6 months. These time scales were longer than the time scales related to P. The partial correlation coefficients between NDVI and PET, P of forest vegetation were higher in northern China, whereas the spatial distribution of related time scales was the opposite. The partial correlation coefficients between NDVI and PET, P of forest vegetation were higher in northern China. However, the spatial distribution of related time scales was the opposite. The correlations between NDVI and PET, P of cropland vegetation and the time scales related to PET had clear spatial heterogeneity. The time scale of the correlation between NDVI and P for cropland in the northern China was about 2 months. P had a strong influence on the growth of various types of vegetation in the study area, and grassland vegetation was affected by P over the shortest time scale. We compare and analyze the results of this study with other related studies. These results provide a reference for exploring the dynamic changes in different vegetation types and factors impacting them.

Increased harvested carbon of cropland in China

Crop harvested carbon (HC) is one of the most important components of the carbon cycle in cropland ecosystems, with a significant impact on the carbon budget of croplands. China is one of the most important crop producers, however, it is still unknown on the spatial and temporal variations of HC. This study collected statistical data on crop production at the province and county levels in China for all ten crop types from 1981 to 2020 and analyzed the magnitude and long-term trend of harvested crop carbon. Our results found a substantial increase of HC in cropland from 0.185 Gt C yr−1 in 1981 to 0.423 Gt C yr−1 in 2020 at a rate of 0.006 Gt C yr−1. The results also highlighted that the average annual carbon sink removal from crop harvesting in China from 1981 to 2020 was 0.32 Gt C yr−1, which was comparable to the net carbon sink of the entire terrestrial ecosystems in China. This study further generated a gridded dataset of HC from 2001 to 2019 in China by using jointly the statistical crop production and distribution maps of cropland. In addition, a model-data comparison was carried out using the dataset and results from seven state-of-the-art terrestrial ecosystem models, revealing substantial disparities in HC simulations in China compared to the dataset generated in the study. This study emphasized the increased importance of HC for estimating cropland carbon budget, and the produced dataset is expected to contribute to carbon budget estimation for cropland ecosystems and the entire China.

Spatiotemporal variations of non-farming use of cropland in China under different SSP-RCP scenarios

Spatiotemporal variations of non-farming use of cropland in China under different SSP-RCP scenarios

Incorporating suburban cropland into urban green infrastructure: A perspective of nature-based solutions in China

Urban green infrastructure (GI) addresses human social development issues and challenges through urban green space ecosystem services. However, the ecosystem service functions of suburban cropland, especially regulating services and cultural services, have been seriously underestimated. The distribution of green spaces and suburban cropland varies in different regions of China, as well as their potential development methods. This article examines the potential of integrating suburban cropland into urban green infrastructure, offering a perspective on nature-based solutions in China. We divided the suburban cropland in China into three parts: peri‑suburban, mid-suburban, and outer-suburban by the concept of 15-minute living circle based on different travel modes of people. Based on statistical yearbook data, satellite remote sensing images and the fragstats 4.2 programme, a quantitative analysis was conducted on the spatial distribution, landscape pattern and social development of suburban farmland and green space in four cities. Then, the potential for improving the exposure level of suburban cropland after incorporating suburban cropland into urban green infrastructure was quantified and compared. Finally, we explored the potential development of the three kinds of suburban cropland as green infrastructure based on the concept of NbS. We found the spatial pattern of cropland and green space in the mid-suburban is greatly affected by regional geographical conditions, the green exposure level, i.e., green space availability indicators, in Beijing, Shanghai, Guangzhou, and Xi'an increased by 83 %, 300 %, 24 %, and 612 %, respectively, after incorporating suburban cropland into urban green infrastructure. The potential development models for suburban cropland should be based on NbS and China's national conditions: peri‑suburban cropland should be fully utilized for cultural and social functions, the mid-suburban cropland should focus on multifunctional utilization of cropland, and the outer-suburban is prioritized for ecological functions. Our study provides scientific insights for deep exploration of the functions of suburban cropland in China.

Uphill cropland and stability assessment of gained cropland in China over the preceding 30 years

Uphill cropland and stability assessment of gained cropland in China over the preceding 30 years

Assessing the environmental impact of agricultural production structure transformation — Evidence from the non-grain production of cropland in China

Achieving low-carbon agricultural development is a requirement of the United Nations Sustainable Development Goals (SDGs). A sustainable agricultural production structure not only ensures food security but also promotes efficient resource utilization and environmental protection. However, the current research has not yet assessed the environmental impact of the agricultural production structure transformation, particularly in relation to the non-grain production of cropland (NGPC). By calculating the carbon emission intensity (CEI) and NGPC in 338 cities across China from 2000 to 2021, this study analyzes their spatiotemporal characteristics. A Spatial Autoregressive (SAR) model has been used to assess the environmental impact of the agricultural production structure transformation. The findings show a spatial correlation between NGPC and CEI, and the NGPC will exacerbate the CEI. In addition, variations exist in the impact of different grain production functional areas. The NGPC in the Production and Sales Balance Area (PSBA) and the Major Grain Production Area (MGPA) have led to an increase in the CEI, while the Major Grain Sales Area (MGSA) has had a contrasting impact. Assessing the environmental impact of agricultural production structure transformation at the city level can offer valuable insights for achieving sustainable transformation.

A global estimate of monthly vegetation and soil fractions from spatiotemporally adaptive spectral mixture analysis during 2001–2022

Abstract. Multifaceted regime shifts of Earth's surface are ongoing dramatically and – in turn – considerably alter the global carbon budget, energy balance and biogeochemical cycles. Sustainably managing terrestrial ecosystems necessitates a deeper comprehension of the diverse and dynamic nature of multicomponent information within these environments. However, comprehensive records of global-scale fractional vegetation and soil information that encompass these structural and functional complexities remain limited. Here, we provide a globally comprehensive record of monthly vegetation and soil fractions during the period 2001–2022 using a spatiotemporally adaptive spectral mixture analysis framework. This product is designed to continuously represent Earth's terrestrial surface as a percentage of five physically meaningful vegetation and soil endmembers, including photosynthetic vegetation (PV), nonphotosynthetic vegetation (NPV), bare soil (BS), ice or snow (IS) and dark surface (DA), with high accuracy and low uncertainty compared to the previous vegetation index and vegetation continuous-field product as well as traditional fully constrained linear spectral mixture models. We also adopt nonparametric seasonal Mann–Kendall tested fractional dynamics to identify shifts based on interactive changes in these fractions. Our results – superior to previous portrayals of the greening planet – not only report a +9.35 × 105 km2 change in photosynthetic vegetation, but also explore decreases in nonphotosynthetic vegetation (−2.19 × 105 km2), bare soil (−5.14 × 105 km2) and dark surfaces (−2.27 × 105 km2). In addition, interactive changes in these fractions yield multifaceted regime shifts with important implications, such as a simultaneous increase in PV and NPV in central and southwestern China during afforestation activities, an increase in PV in cropland of China and India due to intensive agricultural development, a decrease in PV and an increase in BS in tropical zones resulting from deforestation. These advantages emphasize that our dataset provides locally relevant information on multifaceted regime shifts at the required scale, enabling scalable modeling and effective governance of future terrestrial ecosystems. The data about five fractional surface vegetation and soil components are available in the Science Data Bank (https://doi.org/10.57760/sciencedb.13287, Sun and Sun, 2023).

Impact of Intercropping on Nitrogen and Phosphorus Nutrient Loss in Camellia oleifera Forests on Entisol Soil

Soil and water loss represent a significant environmental challenge in purple soil cropland in China. However, the quantity and mechanism of nutrient loss from purple soil remain unclear. To understand water and soil conservation and address nitrogen (N) and phosphorus (P) mitigation in Camellia oleifera forest stands on purple soil slope farmland, this study aimed to explore the resistance control effect of forest stands on N and P loss in such agricultural landscapes. In the study, a runoff plot experiment was conducted in purple soil slope farmland. The experiment included three distinct treatments: intercropping of oil tea (Camellia oleifera) and ryegrass (Lolium perenne L.), Camellia oleifera monoculture, and barren land served as the control treatment (CK). Water samples were collected and analyzed from the soil surface runoff and the middle soil layer at a depth of 20 cm (interflow) in three treatment plots under natural rainfall conditions in 2023. Various nutrient components, including total nitrogen (TN), dissolved nitrogen (DN), nitrate nitrogen (NO3−-N), ammonium nitrogen (NH4+-N), particulate nitrogen (PN), total phosphorus (TP), dissolved phosphorus (DP), phosphate (PO4+-P), and particulate phosphorus (PP), were measured in the water samples. The results indicated that intercropping effectively mitigated the loss of various forms of N and P in both surface runoff and interflow within purple soil slope farmland. Compared to the CK, the ryegrass intercropping reduced TN and TP loss by 29.3%–37.3% and 25.7%–38.9%, respectively. The ryegrass intercropping led to a decrease in the average total loss of TN, DN, NO3—N, and NH4+-N by 63.0, 24.3, 4.5, and 6.8 g/ha, corresponding to reductions of 33.3%, 47.6%, 58.3%, and 49.1%, respectively, compared to the CK. The average total loss of TP, DP, and PP decreased by 4.4, 1.8, and 1.4 g/hm2 in the intercropping, reflecting reductions of 32.3%, 31.3%, and 31.1%, respectively. The most significant proportion was observed in PN and PP within the runoff water solution, accounting for 53.3%–74.8% and 56.9%–61.0% of the TN and TP, respectively. These findings establish a foundation for purple soil and water conservation. The research provides valuable insights for land management and policymakers in developing erosion prevention and control programs for sloping cultivated land with Camellia oleifera forests in purple soils. Additionally, it offers guidance for soil and water conservation and prevention of surface source pollution in purple soil regions.

Multifunctional Evaluation and Analysis of Synergistic Relationships: A Cognitive Framework for the Sustainable Use of Cropland in China

Cropland is a comprehensive system influenced by the natural environment and human activities. This article collects the data of cropland use, soil, and other geographic, social and economic factors in the study area and then uses the methods of system analysis, induction and deduction to propose a new research perspective for establishing a cognitive framework and analyzing cropland resources and their functions. The framework is used to assess the rapidly urbanizing region of Guangzhou and investigate the production, ecological, and living functions provided by cropland resources. Synergistic relationships between functions are analyzed using the hot and cold spot methods. The results indicate that the production function of cropland resources in Guangzhou is good, the ecological function is favorable, and the living function is relatively low. A synergistic relationship between the three functions is observed in 91% of areas of Guangzhou, whereas a balanced relationship occurs in some areas of the southern part of Zengcheng, the northwestern and northeastern parts of Conghua, and the western part of Nansha. This research provides guidance for managing cropland resources and ensuring their sustainable utilization.

Carbon storage in mollusk shells: An overlooked yet significant carbon sink in terrestrial ecosystems

Mollusks, the second largest animal family, are found in a variety of ecosystems. As they grow, their shells absorb carbon and form calcium carbonate, making them an important storage place for carbon. However, the amount of carbon deposited in the carbonate shells of terrestrial mollusks throughout modern and geological history has not been quantified. In this study, we first conducted an investigation of carbon deposits in shells from various mollusk species at 470 modern surface soil sample sites across diverse terrestrial ecosystems in China. The deciduous broadleaf forest and shrublands exhibited a higher carbon deposition rate of ∼1.37 ± 2.15 and ∼1.56 ± 2.92 g C m−2/yr−1, while croplands and grasslands displayed a rate of ∼1.11 ± 1.95 and 1.07 ± 1.78 g C m−2/yr−1, respectively. Using geostatistical methods, we estimated the total shell carbon deposition of grassland, forest, shrublands, and croplands in China to be ∼3.39–5.45 × 106 t C yr−1, constituting ∼1.68–2.71 % of China's terrestrial carbon sink, an overlooked portion in previous studies. Additionally, we provided quantitative data on shell carbon fluxes spanning a remarkable 20,000-year period through over ten fossil sequences from loess deposits. The results underscore the continuous and abundant carbon deposition in mollusk shells across various locations for at least 20,000 years, highlighting the persistence and substantial accumulation of shell carbon deposits over time. Remarkably, we estimated that the total shell carbon deposition of loess sediments in China and the world over the past 20,000 years may reach 1.10 × 108 t C and 1.29 × 109 t C, roughly equivalent to an afforestation area of 2.32 × 106 km2 and 2.72 × 107 km2, respectively.

Is Abandoned Cropland Continuously Growing in China? Quantitative Evidence and Enlightenment from Landsat-Derived Annual China Land Cover Dataset

Abandoned cropland is a great waste of land resources, which not only affects the stability of food production, but also wastes limited cropland resources. China has large areas of abandoned cropland, and accurately extracting the large-scale abandoned cropland is a prerequisite for the government to implement reclamation policies and estimate the food production potential of abandoned cropland. China has implemented the Grain for Green Project (GGP) since 1980, but most research has not considered its impact on the extraction of abandoned cropland. Therefore, a method was proposed to identify abandoned cropland excluding the regions of GGP, and to analyze the spatio-temporal characteristics and potential of abandoned cropland in China from 1991 to 2018. GGP potential and food production potential of abandoned cropland were discussed. The results showed that 26.47 million hectares of cropland has been abandoned in the past 28 years (including cropland that has been reclaimed). Under the positive influence of the government’s food security policy, the abandoned cropland has decreased in recent years, but the total area is still high. The abandonment mainly occurred in the Jiangnan Hills, the Hilly Regions of Fujian and Guangdong Province, the North China Mountains, and Eastern Inner Mongolia. The higher the elevation and the steeper the slope, the higher the abandonment rate. In addition, the urban-rural income gap significantly affected the abandonment rate. This study drew the spatial and temporal distribution map of abandoned cropland in China with a spatial resolution of 30 m considering GGP. It provides an important basis for formulating reclamation and GGP policy.

Abandoned cropland compensates the decrease in net ecosystem productivity of impervious surface expansion in China

Abandoned cropland and impervious surface expansion are generally considered to have positive and negative impacts on net ecosystem productivity (NEP), respectively. However, the comprehensive comparison of the impacts of these two land use changes on NEP remains lacking. We use multi-year land cover data, NEP data, and statistical data to track the interannual variability of abandoned cropland and impervious surface expansion in China, and subsequently estimate their impacts on NEP. From 2000 to 2019, 30.8 × 106 ha of cropland in China was abandoned, while the impervious surface area expanded by 8.97 × 106 ha over the period. The average annual abandonment rate and impervious surface expansion rate were 0.83% and 2.96%, respectively. The average annual NEP of abandoned cropland and impervious surface expansion were 39.9 g C/m2 and 16.2 g C/m2, respectively. Using the space-for-time method to estimate NEP changes, results showed that the carbon sink of 0.013 Tg C accumulated by abandoned cropland not only offset the carbon source of 0.01 Tg C from impervious surface expansion but sequestered additional 0.003 Tg C during the study period. Further analysis of the relationships between NEP and natural and anthropogenic factors revealed that temperature had the most significant positive impact on NEP (0.35, p < 0.01), while the urbanization rate had the most significant negative impact on NEP (−0.33, p < 0.01). This study provides a new insight for regulating the effects of land use changes on natural carbon sink/source, and highlights the importance of abandoned cropland to enhancing natural carbon sink.

Enhancing soil carbon and nitrogen through grassland conversion from degraded croplands in China: Assessing magnitudes and identifying key drivers of phosphorus reduction

Agricultural intensification has resulted in severe degradation of croplands in China. While the conversion of degraded croplands to grasslands has been proposed as a potential solution, the effects on soil organic carbon (SOC) and nutrients remain uncertain due to the complex interactions between plant growth and nutrient cycling. To identify key drivers and evaluate general patterns, a meta-analysis of 204 studies was conducted to evaluate changes in SOC, soil nitrogen (N), phosphorus (P), and soil enzyme activities in the 0–40 cm soil layer following grassland conversion across China. Our results showed that grassland conversion increased SOC (16 %), total N (TN, 12 %), available N (AN, 7 %), microbial biomass C (MBC, 48 %), microbial biomass N (MBN, 39 %), and the activities of urease (38 %) and phosphatase (64 %). However, the conversion decreased soil pH (−1 %) and available P content (AP, −26 %). The reduction in AP could be attributed to the restored grasslands absorbing more AP for growth. The duration of conversion was a major factor influencing changes in SOC, TN, and urease activities. Furthermore, mean annual precipitation had a significant impact on soil pH, TP, AP, MBC, and phosphatase activities. Our findings suggest that converting degraded croplands to grasslands can improve soil C and N content in China; however, these findings should be interpreted in the context of the entire recovery process. Further research and mitigation measures, such as the addition of soil P sources, may be required to address this decline in AP.