The production and consumption of pig feed grain have gradually become the primary factor affecting China's food security. The grain consumption coefficient, which is easily influenced by the natural environment and economic conditions, is the core of reasonable estimation of feed grain demand. Therefore, it is important to clarify the spatial and temporal variation characteristics. Accordingly, taking pigs as an example, we measured the spatial and temporal variations of the grain consumption coefficient and the possible causes of different feeding scales in different provinces from 2000 to 2018. The conclusions can be drawn as follows: (1) The grain consumption coefficients of a backyard, small-scale, and the average value of all the scales showed an increasing trend while those of the medium and large scales showed a decreasing and then an increasing trend. (2) The gap between the grain consumption coefficients of different scales was narrowed gradually with the decreasing percentage of concentrated feed costs. (3) The grain conversion efficiency and time efficiency of a large scale were higher than those of other scales. (4) Except for backyard feeding, the grain consumption coefficients of other scales were higher in northern China and lower in southern China while those of the central region of China were higher than the eastern and western regions. The high grain conversion coefficient of consumption in northern China may be due to the fact that pigs need more energy to protect themselves from cold and need to consume more feed, while the differences in southern China may be related to the breed and feed type composition of the pigs. In addition, in order to improve efficiency and save food, it is significant to promote the large-scale pig feeding pattern, to standardize, intensify, mechanize and automate the construction of pig rearing, and to improve the efficiency of pig breeding. Large-scale farming should be distributed in Xinjiang, Qinghai, Sichuan, Guangxi, Hebei, Shandong, and Henan, and over-farming is not recommended in the northeast region as well as Hubei and Hunan. Provinces in the central region, such as Sichuan, Shaanxi, Guizhou, and Hunan, are appropriate for backyard pig farming. To improve feed utilization efficiency, it is advisable to promote large-scale pig breeding.

China has faced severe challenges from the tight balance of food security and the pollution caused by the excessive use of agricultural fertilizers. How to optimize the fertilizer uses to ensure national food security and agricultural environmental sustainability has become a great concern. The purpose of this paper is to explore ways to optimize the application of chemical fertilizer under the joint framework of economic rationality and environmental sustainability in major grain-producing areas. Using the survey data from 1026 wheat-growing farmers in Handan, Hebei province, we build a quantitative model of small holders' use of chemical fertilizers to analyze the obstacles in achieving economic rationality and environmental sustainability simultaneously. The results show that farmers' expectation of chemical fertilizer's output elasticity in the sampling region is significantly higher than the actual elasticity, indicating that, generally speaking, the farmers overestimated the effect of fertilizer on improving grain production, thus using more fertilizers. Meanwhile, the current price of chemical fertilizer in the study area is about half of the optimal price estimated in the analysis, indicating that the cost of chemical fertilizers is relatively low compared with other agricultural inputs, e.g., labor, thus farmers tend to be more dependent on chemical fertilizers in pursuing higher yield. Hence, taking into account the national food security and agricultural environment sustainability, our results suggest that: (1) It is necessary to correct farmers' cognitive bias towards the (in-)effectiveness of fertilizer use to promote scientific fertilization; (2) Fertilizer market structure and the relative price between synthetic and organic fertilizers should be more differentiated through the supply-side reform, so as to fundamentally mitigate fertilizer 'overuse' in China.

At present, Chinese residents' dietary consumption structure is upgrading, changing from a subsistence type to a comprehensive well-off type and from traditional home cooking to modern convenience. Changes in the structure and level of dietary consumption will affect China's future food consumption. Judged from the development law of food consumption of residents in Taiwan, China, the overall gap between the current level and the stable state under the affluent level of Chinese residents' dietary consumption is about 53%, and the gap of animal food consumption is more than doubles. In the past, Chinese residents mainly used grains and vegetables as their main food. Now, they increase consumption of high value-added foods such as animal foods and fruits. China's nominal self-sufficiency rate of grain dropped to 85% in 2018, and that of soybean dropped to 15% at the same time. The self-sufficiency rate of virtual farmland was only 72.6%. Then, China needs to import not only a large amount of protein feed, but also a considerable amount of energy feed. It is concluded that it is difficult to maintain the demand for agricultural products only relying on China's local agricultural production resources. China should rely on domestic production and the international market to ensure food security. To protect the ecological environment, China should import more animal products, especially beef and lamb, appropriately liberalize the import volume of food products, self-produced fruits, and vegetables.

Food waste and its resulting resources and environmental problems are closely related to global food security, while reducing food waste is gradually considered as Plan B for it. As the main part of food waste at the consumption segment, food waste generated by consumer is the main source of food loss and waste. In this study, the direct weighing method was adopted to obtain first-hand data of food waste of residents in typical areas of China (Beijing, Shanghai, Sichuan, Shandong, Henan and Tibet), and for the first time, the total scale of food waste of residents' consumption and its resource and environmental effects were measured on a national scale. The results show that: (1) In 2018, a total of 34 million tons (67.33 g/d per capita) of food was wasted at the consumer segment in China. Grain waste accounted for the largest proportion (35.44%), followed by vegetables (34.83%) and meat (15.38%). (2) In 2018, food waste occupied 63 million hm² of ecological footprint in China, and the per capita ecological footprint was 448 m². Based on 1.5 hm² of ecological footprint per capita in China, the ecological niche of 42 million people was encroached. Aquatic products (39.28%) and meat (34.22%) accounted for the largest ecological footprint of food waste, amounting to 24.56 million hm² and 21.40 million hm², respectively. The research results are helpful to promote the reduction of food waste at the consumption segment, and have important reference value and significance for alleviating the environmental impact and resource consumption pressure of food waste and improving global food security.

Cultivated land abandonment has a profound impact on China's food security. Taking the main grain producing areas in China as an example and based on the identification of the distribution of abandoned land, this paper measured the spatial distribution pattern of abandoned land, established the mediating effect model of cultivated land abandonment, and explored the influence mechanism of cultivated land abandonment on regional grain yield. The results showed that: (1) The area of abandoned cultivated land in the main grain producing areas of China was 4.0553 million hectares, with a rate of 5.85%; the distribution of abandoned land presented a T-shaped pattern, mainly concentrated in the Northeastern Heilongjiang, Northwestern Jilin and Southern Inner Mongolia. (2) Cultivated land abandonment had a significant negative impact on the grain yield of the main grain producing areas. In 2017, these areas lost a farmland production potential of 13.3915 million tons, and the loss of grain output was as high as 22.656 million tons, accounting for 4.69%; Inner Mongolia was the most affected region. (3) Grain sown area, farmland production potential, and agricultural technology input all played an intermediary role, and their regression coefficients were -0.194, -0.025 and 0.006, respectively. (4) We should follow the trend of urban-rural integration and agricultural-rural development, strengthen the input of modern agricultural production factors and policy support in major grain producing areas, and construct the flexible mechanism of spatial transformation between grain production and cultivated land fallow to ensure food security in China.