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Whether China can achieve the United Nations' Sustainable Development Goals (SDGs) largely depends on the ability of main food-producing areas to cope with multiple land use change challenges. Despite the fact that the Yangtze River basin is one of the key regions for China's food security, the spatiotemporal dynamics of cropland abandonment and recultivation remain largely unexplored in this region. The present study assesses the evolution of the agricultural system within the Yangtze River basin between 2000 and 2020 by mapping cropland abandonment and recultivation using MODIS time series and multiple land cover products. The results highlight a widespread cropland abandonment process (i.e., 10.5% of the total study area between 2000 and 2020), predominantly in Western Sichuan, Eastern Yunnan, and Central Jiangxi. Although 70% of abandoned cropland is situated in areas with slopes less than 5°, the highest rates of abandonment are in mountainous regions. However, by 2020, 74% of this abandoned cropland had been recultivated at least once, whereas half of the abandoned croplands got recultivated within three years of their initial abandonment. Hence, as this is one of the first studies that unravels the complex interaction between cropland abandonment and recultivation in a spatiotemporal explicit context, it offers (i) scientists a novel methodological framework to assess agricultural land use issues across large geographical entities, and (ii) policy-makers new insights to support the sustainable transition of the agricultural sector. [ABSTRACT FROM AUTHOR]

Multiple cropping is a widespread agricultural practice that can partly reflect cropland use intensity. Previous studies have largely focused on harvest frequencies within an annual (e.g., multiple cropping frequency [MCF]) or multiannual basis. However, the complexity of cropland use intensity, which combines different cropping and fallow strategies, has not been fully investigated. Moreover, such information is particularly lacking at the regional scale. This study proposed a new perspective of multiple cropping system (MCS), and developed a method for mapping stable MCSs for a prolonged time. We selected an agricultural region (Poyang Lake Plain, Jiangxi Province, China) and proposed four stable MCSs in terms of the number of crops (C) grown in a given number of years (Y) defined by the length of crop rotation: Continuous single-cropping system (1C/1Y), continuous double-cropping system (2C/1Y), and two alternating systems (3C/2Y and 5C/3Y). To map MCSs, we first obtained the remote-sensing-observed annual MCF from 2001 to 2018. Second, total harvests, frequency, and continuity were proposed based on multi-year MCF information to classify each pixel as one of the four proposed MCSs. Total harvests were defined as the total number of harvests over the observation period. Frequency was defined as the total number of rotation units over the observation period for a given MCS. We defined continuity as the largest number of consecutive years under a given MCS. Finally, we determined the final type of an MCS using decision rules considering the three indicators. The results showed that the overall accuracy of the MCF maps were > 90%, and the overall accuracy of MCS map was 87.8%. We found that 84.4% of croplands could be characterized as one of the four MCSs: 2C/1Y accounted for the largest area (38.1%), followed by the two alternating systems (together they accounted for 48.6% of the total), and finally 1C/1Y. The results of our study suggest that multiple cropping practices should be characterized from the cropping system perspective. The MCS mapping method has great potential for large-scale crop rotation system mapping, and the MCS mapping results could help explore the combined effects of different cropping systems and further provide strategies for optimizing the spatially adapted practices in agricultural land systems. [Display omitted] • The complexity of cropland use intensity that combines different cropping and fallow strategies has not been fully studied. • Multiple cropping systems (MCSs) depict the fluctuating changes in multiple cropping frequency across years. • We developed a method for mapping MCSs through a case study and using decision rules and indicators. • Almost half of the MCSs alternate single-cropping and double-cropping regularly rather than keeping constant. • Multiple cropping practices should be characterized from the cropping system perspective. [ABSTRACT FROM AUTHOR]

Cropland intensification promises additional food supply without further expanding croplands into natural ecosystems. Cropland use intensity measures the degree of intensification by various indicators, both from input and output perspectives; all of these indicators are however not always coherent—which may cause confusion and send contradicting signals to policymakers. Few empirical studies have been conducted to relate and compare various intensity indicators. In this study, we start with a hypothesis that cropland use intensity measured by different indicators may differ. We then test such a hypothesis based on empirical evidence in a typical multi-cropped region (i.e., Jinxian County) in Jiangxi Province—a major breadbasket in Southern China. We focus on two widely used indicators, i.e., multi-cropping frequency (MCF) and crop growth duration (GD a), measured by a hybrid time-series remote sensing dataset which fuses MODIS and Gaofen-1 images for the year 2015. We map these two indicators independently at a 16 m spatial resolution. For each pixel, MCF takes value from 1 to 3 corresponding to single-, double- and triple- cropping; while GD a is quantified by the accumulative crop growth days within the study year. We relate the values of two indicators, summarize the descriptive statistics of GD a grouped by MCF categories, and compare MCF and GD a values by using a box-whisker chart, a bivariate map, and a set of statistical tests. We find that a significant overlap of GD a exists between single cropping and double cropping both visually and statistically. In other words, the different cropland intensity levels measured by MCF appear to be the same if measured by GD a. The box-whisker chart shows that the GD a of single cropping in the upper quarter is substantially longer than the GD a of double cropping in the lower quarter. The non-parametric tests show that the overlapped GD a between single cropping and double cropping exists substantially, which may cause confusion. Moreover, the bivariate map shows that single cropping with shorter growth duration (i.e., consistent low intensity) and double cropping with longer growth duration (i.e., consistent high intensity) account for 44% and 28%, respectively, while the rest manifested as inconsistent which accounts for another 28% of the total cropland area. These results confirm our hypothesis—the inconsistency among intensification indicators. Different measurements may convey contradicting messages for policymakers in pursuing the sustainable intensification goals, which suggests more efforts are required to understand the multidimensionality of the process of cropland intensification for distinct policy measurements. [Display omitted] • Cropland use intensity can be measured by various indicators which are not always coherent and consistent. • We hypothesized that cropland use intensity measured by different indicators may differ. • We found that about 28% of croplands displayed inconsistent intensity in a case study. • The substantial inconsistency indicates that measuring and interpreting cropland use intensity are equally important. • We need to better understand the multidimensionality of cropland intensification for distinct policy measurements. [ABSTRACT FROM AUTHOR]