Heavy metal pollution in soil is threatening the ecological environment and human health. However, field measurement of heavy metal content in soil entails significant costs. Therefore, this study explores the estimation method of soil heavy metals based on remote sensing images and machine learning. To accurately estimate the heavy metal content, we propose a hybrid artificial intelligence model integrating least absolute shrinkage and selection operator (LASSO), genetic algorithm (GA) and error back propagation neural network (BPNN), namely the LASSO-GA-BPNN model. Meanwhile, this study compares the accuracy of the LASSO-GA-BPNN model, SVR (Support Vector Regression), RF (Random Forest) and spatial interpolation methods with Huanghua city as an example. Furthermore, the study uses the LASSO-GA-BPNN model to estimate the content of eight heavy metals (including Ni, Pb, Cr, Hg, Cd, As, Cu, and Zn) in Huanghua and visualize the results in high resolution. In addition, we calculate the Nemerow index based on the estimation results. The results denote that, the simultaneous optimization of BPNN by LASSO and GA can greatly improve the estimation accuracy and generalization ability. The LASSO-GA-BPNN model is a more accurate model for the estimate heavy metal content in soil compared to SVR, RF and spatial interpolation. Moreover, the comprehensive pollution level in Huanghua is mainly low pollution. The overall spatial distribution law of each heavy metal content is very similar, and the local spatial distribution of each heavy metal is different. The results are of great significance for soil pollution estimation.

Scholars have paid much attention to the problems existing in the land expropriation risk assessment system and the sound countermeasures from a qualitative perspective. Empirical research on land expropriation social stability risk assessment from the micro-level perspective is limited. This study analyzed the Chinese social stability risk assessment system of land expropriation though a case study of a land expropriation project in China. The current social stability risk assessment system of land expropriation, which includes the assessment purposes, principles, contents, methods, and results, was analyzed. We concluded with lessons and deficiencies from the current social stability risk assessment system. The research findings show that: (1) the current land expropriation risk assessment system mostly takes the land administration department as the main body of responsibility, identifies the risks by means of seminars, visits, letters, and visits, and takes the opinion of the masses or experts as the risk assessment result. (2) The current land expropriation risk assessment system should be standardized in terms of defining the risk assessment of land expropriation, improving the land expropriation risk assessment system and optimizing land expropriation assessment procedures. This paper provides a reference for the sustainable development of land use in rural and urban areas in China.

The pattern of international agricultural trade is undergoing profound changes. The influence of country risks on the international agricultural trade pattern is prominent. In this paper, we comprehensively analyze the international agricultural trade patterns and explore the influence of country risks on them. Specifically, we first construct an international agricultural trade network (IATN) based on complex network theory. Second, we analyze each country’s diversity of import sources and the position of countries in the IATN using the Herfindahl–Hirschman Index (HHI) and network indicators, such as in-degree, out-degree, weighted in-degree, weighted out-degree, and betweenness centrality. Third, this paper explores the influence of different types of country risks, including economic risk and political risk, on international agricultural trade patterns using the panel regression method. The results show that countries played different roles and occupied different positions in the international agricultural trade pattern; notably, the United States occupied a core position, while Japan and Mexico had insufficient diversity in import sources. Moreover, based on the panel regression method, we find that political risks have a positive impact on the agricultural trade pattern, while an unstable economic environment could inhibit the agricultural trade pattern in various countries. This study could provide references for countries to implement agricultural trade policies regarding country risks to ensure stable agricultural trade relations and national food security.

Chemical fertilizer is one of the most important input factors in agricultural production, but the excessive use of fertilizer inevitably leads to the loss of agricultural eco-efficiency (AEE). Therefore, it is necessary to explore the impact of fertilizer use intensity (FUI) on AEE. However, ordinary panel regression, based on the assumption of parameter homogeneity may yield biased estimation conclusions. In this regard, a panel quantile regression model (QRM) was constructed with the provincial panel data of China from 1978–2020 to test the difference and variation of this impact under heterogeneous conditions. The model was then combined with the spatial econometric model to explore the effect of the spatial lag factor. The results are as follows: (1) The QSM has unveiled a great improvement space for AEE that remains low overall, despite displaying a rising trend; the highest AEE is in the eastern region. (2) The FUI has a significant negative effect on AEE with the rise in quantiles, this negative effect tended towards weakening overall, although it rebounded slightly; it was stronger in areas with low AEE. It is necessary to consider the heterogeneous conditions in comparison with the average treatment effect of ordinary panel econometric regressions. (3) The impact of FUI shows significant variability in different economic sub-divisions and different sub-periods. (4) After considering the spatial effect of fertilizer use, the negative influence on local AEE had a faster decay rate as the quantile rose, but could produce a positive spatial spillover effect on AEE in neighboring areas. Local governments should dynamically adjust and optimize their fertilizer reduction and efficiency improvement policies according to the level and development stage of their AEE to establish a complete regional linked agroecological cooperation mechanism.

Farmers’ satisfaction with reform of the land expropriation system has not been fully examined, so it is difficult to comprehensively and successfully judge the effectiveness of the reforms. Traditional statistical methods cannot accurately explain the relationship between the variables. In order to fully understand the implementation, progress, and applicability of land expropriation system reform, this paper analyzes the factors influencing farmers’ satisfaction, presents the shortcomings of land expropriation system reform, and puts forward improvement suggestions. Taking the land expropriation system reform pilot in Dingzhou city as an example, this paper investigates the satisfaction of the farmers who have had their land expropriated by establishing a structural equation model (SEM) to obtain feedback on the implementation effect of the pilot work. The results show that the factors affecting farmers’ satisfaction with the reform of land expropriation systems can be summarized into four variables: land expropriation compensation standard, land income distribution, land expropriation security mode, and land expropriation procedure. The parameter estimation between these four potential variables and their corresponding observation variables shows that, in the process of land expropriation, the comparison of land expropriation compensation standards and observation variables with market entry projects is an important factor affecting the satisfaction of farmers with regard to land expropriation. The income of municipal and county governments and village collective incomes have a great impact on farmers, indicating that the satisfaction of farmers is not only related to the absolute level of compensation and income, but is also affected by the relative level. In addition, providing farmers with a variety of reasonable security methods is an important element to enable the smooth progress of land expropriation. Furthermore, attention should also be paid to the formulation of land expropriation schemes and emergency plans to solve land expropriation conflicts.