*2.1. Study Area*

The maize field trial was conducted at Youyi Farm, Youyi County, Heilongjiang Province in China (46◦44 N, 131◦40 E), which covers an area of approximately 17.29 hectares. The area has a temperate continental monsoon climate with four distinct seasons, rain and heat occur during the same period, and the soil type is dark brown soil with high fertility.

The maize planted in this experimental plot was sown on 6 May 2019, and harvested on 14 September 2019. Maize lodged on 28 July 2018, and multispectral imagery (Figure 1) was acquired on 12 September 2019. In the study site, which is a ffected by natural factors such as high winds, di fficult terrain, and soil, water, and fertilizer transportation problems, maize development is diverse and exists in both development and mature periods. In Figure 1c, the typical yellow areas show maize in the mature period, and its growth is better than that of the typical green area maize in the development period. Maize lodging can be divided into the two groups shown in Figure 2: Lodging S and Lodging R. Compared with Lodging S, Lodging R is more serious. The nonlodging maize includes three classes (Figure 2): maize with green leaves (No-Lodging G), maize with yellow leaves (No-Lodging Y), and maize with yellowish leaves (No-Lodging LY). The growth of No-Lodging LY is better than that of the other two categories. Influenced by the edge e ffect [17], the growth status of No-Lodging Y is the worst.

**Figure 1.** (**a**) The location of Youyi County in China (red area); (**b**) the location of the study site in Youyi County (red area); and (**c**) the multispectral imagery of the study site.

**Figure 2.** Types of lodging and nonlodging maize.
