Decoupling relationship between greenhouse gas emissions from cropland utilization and crop yield in China: implications for green agricultural development.

Developing low-carbon utilization of cropland is critical to coordinate agricultural production and environmental protection. Based on a theoretical analysis of greenhouse gas (GHG) emissions and crop production, this study examined the GHG emissions from cropland utilization in China and the decoupling process from crop yields with consideration of different sources and then explored the driving factors in different regions. The results showed that the GHG emissions from cropland utilization in China rose first and then fell between 2003 and 2020, and the decoupling process has undergone three stages, namely "expansive coupling", "weak decoupling", and "strong decoupling". And the eastern and southern provinces are relatively ahead of the western and northwestern provinces. Additionally, crop yields have been basically decoupled from GHG emissions caused by agricultural inputs, but they were still not decoupled from GHG emissions from cropland in Northeastern and Northern China. Among the influencing factors, utilization efficiency has promoted the decoupling progress, the input structure has played a promoting role in the early stage and hindered it later, and the input intensity and the scale have worked as hindering factors. Policy implications have been proposed to support the sustainable development of agriculture.

Risk assessment and validation of farmland abandonment based on time series change detection.

Farmland abandonment, a widespread phenomenon during land-use transition, leads to a cycling or vanishing evolution of farmland resources. As urbanization advances, an increasing number of agricultural laborers migrate from rural to urban areas, causing ongoing farmland abandonment. However, in contrast to the abandoned information extraction and driving mechanisms revelation, the potential risk of farmland abandonment has received insufficient attention. This study took Yangtze River Economic Belt of China as study area, selected multiple aspects to construct a risk assessment system for farmland abandonment, and applied time series change detection to verify the results. The results showed that (1) farmland abandonment risk, with a regional average value of 0.0978, has strong spatial heterogeneity, with high values clustering in Yunnan-Guizhou and Sichuan-Chongqing mountainous areas and low values distributed in the midstream and downstream plains and the Sichuan Basin. (2) The proportion of farmland area gradually decreased as the risk grade increased. Farmland, with low abandonment risk, occupied an area of 204,837 km2, constituting the highest percentage of 35.18% among the overall farmland, and was mainly distributed in the provinces of Jiangsu and Anhui. The area of farmland with high risk was 16,458 km2, only accounting for 2.83%, the majority of which was clustered in Sichuan and Yunnan provinces. (3) The Normalized Difference Vegetation Index (NDVI) time series change detection validated the reliability of the risk assessment system. Samples of farmland having low abandonment risk indeed had the lowest abandonment rate of 10%, and those which indicated high risk had the highest abandonment rate of 32%. We propose differentiated managements for farmland resources with high and low abandonment risk from the perspective of sustainable use. This study provides a more reasonable and scientific system for farmland abandonment risk assessment and helps to fill the research gap.

Urbanization in China drives farmland uphill under the constraint of the requisition-compensation balance.

The slope is an important objective attribute of farmland that changes with the evolution of its spatial pattern. A growing area of plain farmland is being occupied by built-up land owing to rapid urbanization, while the newly added are sloping and terrace farmland under the constraint of the requisition-compensation balance. Researchers have focused on the horizontal spatial redistribution of farmland quantity while ignoring vertical variations in its slope, which is critical for its overall quality. Based on data on land use classification in China from 1990 to 2019, this study uses land use change trajectory as well as trend and driver analyses to identify the impact of urbanization on change in the slope of unstable farmland. The results show the following: (1) The area of unstable farmland accounted for ~20% of all farmland, with its slope increasing from 5.77° in 1990 to 6.25° in 2019 due to conversion in land use. (2) Variation in the slope of unstable farmland had significant heterogeneity, with regions undergoing a significant increase concentrated in the east and those undergoing monotonous decline not spatially clustered. (3) Farmland development and built-up land occupation have driven increases in the slope of unstable farmland with a relatively balanced effect, whereas the trend of increasing has been mainly suppressed by farmland marginalization. (4) The area of urban land expanded by 158,446.70km2 during 1990-2019, 24.15% of which was due to encroachment on farmland with a slope of 1.31°. Farmland development with a slope of 6.98° helped replenish 90.30% of the occupied area. This combined process has led to unstable farmland uphill under the constraint of the requisition-compensation balance. The results here can provide a reference for the protection and sustainable utilization of farmland.

Influence of farmland marginalization in mountainous and hilly areas on land use changes at the county level.

Agricultural works alter earth's surface at the largest scale among human-driven activities. Previous studies have focused more on the reclamation of natural land, however, farmland marginalization (FM), emerging as an important mean of land use changes in mountainous and hilly areas (MHAs) has always been overlooked in the background of production efficiency improvement along with urbanization and population migration. This paper examined the characteristics of the spatial-temporal distribution and conversion of marginalized farmland in the MHAs of China at county level (excluding Hong Kong, Macau, and Taiwan) from 1990 to 2020, regarding farmland in MHAs converted into non-built-up land as FM. The results showed that: (1) The total area of marginalized farmland in the MHAs was 1.03 × 106 km2. The counties with larger area of marginalized farmland were concentrated around the Hu Line, and those with higher ratio were distributed in southern mountainous areas. (2) The area of marginalized farmland in each stage exhibited a fluctuating trend from 1990 to 2020. Forests and grasslands were prioritized as the desirable types in land conversion, and had prominent spatial agglomeration. (3) The influence of FM in MHAs on land use changes at county level demonstrated significant spatial-temporal heterogeneity, with wide range and low intensity from 1990 to 2000 and 2015 to 2020, and narrow range and high intensity from 2000 to 2015, and the counties with high intensity were distributed in the Loess Plateau and Sichuan-Chongqing hilly region. (4) The slope of marginalized farmland exhibited a prominent rule of spatial distribution, but an insignificant temporal trend under the influence of governmental policies. The larger the slope was, the higher the degree of marginalization was, but not necessarily earlier it occurred. The results can provide a reference for the formulation and implementation of farmland protection policies.

Comprehensive Evaluation of Cultivated Land Quality at County Scale: A Case Study of Shengzhou, Zhejiang Province, China.

The existing evaluation system of cultivated land quality mainly considers the natural quality and utilisation conditions, but without sufficient emphasis on ecological environment, which can't meet the requirements of the trinity pattern protection policy. This study, using GIS spatial analysis and multifactor comprehensive evaluation method, constructed a comprehensive evaluation index system, and applied it in Shengzhou. The results show that: (1) under the comprehensive evaluation system, the quality of cultivated land was classified into five levels and revealed normal distribution with the third level cultivated land area as the peak, successive reduction to the two poles, and the overall quality was good relatively; (2) A close relationship was observed between the quality grade of cultivated land and the landform, the valley plain with highest cultivated land quality was the main grain-producing areas. However, the cultivated land in mountainous areas was poor relatively, and vulnerable to geological disasters; (3) The quality grade of cultivated land was related to economical activities directly. The high-quality cultivated land resources made these towns the main grain-producing areas with many agricultural industries distribution. This study provided a new assessment approach that can support cultivated land grading, quality improvement, and sustainable usage, as well as providing a reference for related research and application.

[Land use and land cover charnge (LUCC) and landscape service: Evaluation, mapping and modeling].

Studies on ecosystem service from landscape scale aspect have received increasing attention from researchers all over the world. Compared with ecosystem scale, it should be more suitable to explore the influence of human activities on land use and land cover change (LUCC), and to interpret the mechanisms and processes of sustainable landscape dynamics on landscape scale. Based on comprehensive and systematic analysis of researches on landscape service, this paper firstly discussed basic concepts and classification of landscape service. Then, methods of evaluation, mapping and modeling of landscape service were analyzed and concluded. Finally, future trends for the research on landscape service were proposed. It was put forward that, exploring further connotation and classification system of landscape service, improving methods and quantitative indicators for evaluation, mapping and modelling of landscape service, carrying out long-term integrated researches on landscape pattern-process-service-scale relationships and enhancing the applications of theories and methods on landscape economics and landscape ecology are very important fields of the research on landscape service in future.