## 4 Discussion  
The stability of the area, structure, and quality of cultivated land is fundamental to guaranteeing regional grain productivity. However, paddy fields and drylands showed a net decrease in Hunan Province since 1990. Combining the results of the evaluation of the cultivated land quality and the previous analysis, it can be seen that the reduced paddy field areas were mainly distributed in the area with better conditions of altitude, slope, accumulated temperature, and rainfall, and higher land quality area (e.g., in southern, eastern, and northern Hunan). The changes in the amount, structure, and spatial location of cultivated land caused a continuous decline in GPP, which will harm grain production in Hunan Province because we cannot improve the efficiency of agricultural technology inputs in a short period. However, statistics show that the area of grain sown in Hunan Province has stabilized at approximately 4.95 million hectares, agricultural machinery input has gradually increased, and farmers have improved the efficiency of the food production potential. However, grain production has remained at approximately 30 million tons, with no significant growth. If the area of cultivated land is reduced and the overall quality does not improve, this will inevitably lead to a continued decline in the regional GPP, which will make it difficult to meet the growing demand for food, even if agricultural development becomes more efficient. Moreover, there is a trend where the area of cultivated land and grain sowing continues to decrease under the serious situation of low agricultural economic efficiency, land abandonment, nongrain planting, and aging labor [18; 23; 28]. The current bottleneck in agricultural technology development and the reduction in the grain yield growth rate and how to guarantee regional grain production deserve our most in-depth consideration. We believe that it is particularly important to protect the quantity, structure, and quality of cultivated land to stabilize the regional grain production capacity. From the perspective of the spatial characteristics of cultivated land change, the cultivated land area was significantly reduced when the elevation was \(>\)200 m and the slope was 2\({}^{\circ}\)-15\({}^{\circ}\), although it was not excluded that part of this may be caused by ecological restoration. Combined with the existing research and the authors' observations, it was found that there were indeed increasingly serious cultivated land abandonments in Hunan Province. Some policies strictly prohibit the construction of development zones and towns to occupy abandoned farmland that has been in place since the end of the last century, but allowing the continued existence of abandoned farmland is also a waste of resources, and it has become increasingly difficult to implement cultivated land requisition-compensation balance because of the lack of backup resources for farmland. In addition, some supplementary cultivated land in the area where the slope was bigger than 25\({}^{\circ}\) from 2000 to 2014 resulted in the phenomenon of abandonment in low slopes and reclamation in high slopes. Therefore, can we reutilize abandoned arable land as a new backup resource, especially that with better production conditions? On the one hand, it can increase the efficiency of cultivated land use and grain production; on the other hand, it can reduce the risk of ecological damage caused by cropland reclamation and save land reclamation funds [28]. Therefore, the government needs to attach great importance to the phenomenon of cultivated land abandonment and conduct a comprehensive investigation based on the standardized definition of abandoned cultivated land to know the scale and understand the mechanism of cultivated land abandonment [67; 68; 69], then a utilization plan can be developed, such as fallow rotation, reclamation, and other ways to prioritize the use of abandoned cultivated land where production conditions are good.