sustainability Article Willingness of Farmers to Transform Vacant Rural Residential Land into Cultivated Land in a Major Grain-Producing Area of Central China Yan Tong 1,2, Haipeng Niu 1,2,* and Liangxin Fan 1,2 1 Taihang Development Academy of Henan Polytechnic University, Jiaozuo 454003, Henan...