# Exploring a Moderate Fallow Scale of Cultivated Land in China from the Perspective of Food Security
## 6 Conclusions and Implications  
With food security as the bottom line, this study systematically calculated the GPP of existing and unexcavated cultivated land in China from grain yield per unit reductions, MCI declines, agricultural structure adjustments, and construction land expansion on the basis of the perspective of land use change from 1990 to 2017. The population carrying capacity of cultivated land and the theoretical scale that could be followed were estimated according to different per capita grain consumption levels. The main conclusions are as follows. First, the GPP of cultivated land to be excavated in China was \(7714.69\times 10^{4}\) t. The reserved GPP from grain yield per unit reductions, MCI declines, and agricultural structure adjustments were \(920.67\times 10^{4}\) t, \(4,320.86\times 10^{4}\) t, and \(7,759.82\times 10^{4}\) t, respectively, whereas the lost GPP caused by construction land expansion was \(5286.66\times 10^{4}\) t in the past 30 years. Second, the population carrying capacity of cultivated land in China in 2017 ranged from 1.469 to 1.515 billion on the basis of the well-off consumption standard and the comprehensive grain consumption level, that is, the grain output of cultivated land can fully meet the consumption needs of the existing population. A moderate fallowing scale could be used at this stage, and the fallow scale was between \(850.22\times 10^{4}\) hm\({}^{2}\) and \(1291.57\times 10^{4}\) hm\({}^{2}\). Finally, the lost GPP caused by the occupation of construction land differed greatly depending on economic growth rates. In the low-speed economic growth scenario, China could fallow 5.65% of cultivated land by 2030, and only 0.54% of the cultivated land could be fallowed in 2030 under the scenarios of medium- and high-speed economic growth. At this stage, if the production potential of existing cultivated land is fully tapped, the domestic food demand can be met. This scenario would also provide an opportunity for cultivated land to be fallowed in China. With the development of urbanization, the fallow scale will decrease significantly in the future, especially in the scenarios of medium- and high-speed economic growth, and the fallow scale proportion will be only 0.54% by 2030. Moreover, the grain consumption level of residents will also continue to increase as urban-rural residents' incomes improve, and the promotion of fallow land will also be restricted by food security. Thus, we should promote following as soon as possible at this stage to ensure that the cultivated land has enough time to rest and recover to ensure food security and lay the foundation for sustainable development of fallow farming. In addition, the government should pay attention to excavating the grain production capacity of existing cultivated land. Making full use of the GPP of cultivated land will save a substantial amount of money in land reclamation costs. Additionally, the problems of newly developed cultivated land with poor quality and fragile ecological conditions can be avoided, and the dynamic balance of cultivated land can be realized more sustainably and scientifically. Concerning grain transportation from north to south, the government should pay attention to exploiting the grain productive capacity of cultivated land in South China, which is more conducive to the spatial allocation of grain. The co-authors together contributed to the completion of this article. Specifically, it follows their individual contribution: conceptualization, D.L. and Y.W. ; data curation, H.H., Y.W., and K.S. ; formal analysis, D.L. and Y.W. ; methodology, Q.Y. and Y.W. ; project administration, Q.Y. ; writing--original draft, D.L. ; writing--review and editing, D.L., Y.W., and Q.Y. This work is supported by the Major Project of the National Social Science Fund of China (grant no. 15 ZDC032), the National Natural Science Foundation of China (grant no. 41901232), the Key Projects of the National Natural Science Foundation of China (grant no.