Practice and research progress on spatio-temporal collocation of fallow of cultivated land in world

Abstract: It is a long-term strategy of "storing grain in the ground and storing grain in the technology" for China to carry out rotation and fallow of cultivated land as a system at present. The paper is based on the exploration of the key issues of the spatio-temporal collocation of the cultivated land fallow in China. With the deepening of the pilot work of cultivated land fallow in China, how do we coordinate the spatio-temporal collocation of cultivated land fallow to achieve maximum comprehensive benefits? Following the logical thinking of "experiencing typical national and regional practices, extracting theoretical results, discussing key issues" from the disciplines of geography, agronomy, land science and management, the paper uses the methods of literature, comparison law, induction and field survey, summarizes the practical results of typical countries and regions, and discusses the key problems of the spatio-temporal collocation of cultivated land fallow in China. The following main results are obtained: 1) There are mainly 4 types of spatio-temporal collocation of the cultivated land fallow in typical countries and regions: the aim-oriented spatio-temporal collocation, the execution-oriented spatio-temporal collocation, and the multi-condition-constraint-oriented spatio-temporal collocation, and the technology-oriented spatio-temporal collocation. 2) The connotation essence of the spatio-temporal collocation of cultivated land fallow is to realize the macro-control of "positioning, quantification, and timing" of fallow land, which includes mainly the fallow aim, fallow spatial layout and fallow time arrangement. First, the spatio-temporal collocation is oriented towards fallow aim, and fallow aims at the entire process of spatio-temporal collocation. Second, the fallow spatial layout is to optimize and combine the fallow scale and the fallow area, which are mutually restricted and synchronized. The fallow spatial layout should be considered as national scale and regional scale, including national, provincial, municipal and county scale, and the fallow spatial layout constraints or evaluation index systems at different spatial scales are different. The minimal spatial scale of the fallow scale is county level, while the minimal spatial scale of the fallow area is parcel of land. Third, the fallow time arrangement is regulating and controlling the fallow time series and the fallow time length, which are respectively configured according to the fallow emergency degree and the expected benefits in this area. The fallow time series can be divided into short term, medium term and long term, and the fallow time length can be divided into season break, annual rest and rest of many years. In addition, the spatio-temporal collocation of cultivated land fallow is also controlled by the national conditions and the land system in China, and is shown in the fallow aim or the fallow constraints. 3) The spatio-temporal collocation process of cultivated land fallow is "fallow aim, constraint, spatial layout, time arrangement", and each link is connected with each other. The constraints mainly include grain market, food security, ecological security, cultivated land quality and social economy, and can be transformed with the fallow aim. The fallow spatial layout and fallow time arrangement are subject to constraints, and using different spatial-scale forecasting models or evaluation index systems, and making full use of "3S" (remote sensing, global position system, and geographic information system), monitoring, and surveying and mapping are the technical foundations for rational collocation. 4) The key issues that need to be solved in the spatio-temporal collocation of cultivated land fallow in China are as follows: The first issue is the spatial layout of cultivated land fallow at different spatial scales. Grain security is the primary constraint condition at the national scale, and the geographical spatial difference between grain supply and demand, the quality and ecological condition of cultivated land and the level of regional social economy is the comprehensive constraint condition at regional scale. The second issue is the fallow time arrangement of cultivated land in different regions. According to the urgency level and the expected benefits of the regional fallow, the time series and the multiple fallow lengths of the cultivated land fallow are determined respectively. In fact, the improvement of the cultivated land fallow system in any country is the result of continuous attempts among academics, policymakers and farmers. At present, the pilot work of the cultivated land fallow in China has been explored for more than 2 years, and many problems encountered in the pilot process are still to be thought out in order to improve the timeliness of the spatio-temporal collocation of the cultivated land fallow.