Figure 1

Map of the study area in Henan province. The study area is flat with an average elevation of 90 meters. Optical view of Farm land A, Farm land B, Farm land C, Farm land D and Village A test regions (© Google Earth). Figure done with the ArcMAP 10.3 (https://desktop.arcgis.com/en/arcmap/) and the GMT 5.4 (http://gmt.soest.hawaii.edu/projects/gmt).