## 3 Variables Description and Research Method
### The Threshold Effect Test of China's Agricultural Film Usage on Agricultural Development
\begin{table}
\begin{tabular}{c c c c c c c} \hline
**Province** & **Coef** & **t** & **_p_** & **Province** & **Coef** & **t** & **_p_** \\ \hline Anhui & \(-8.1455\)*** & \(-3.52\) & \(0.001\) & Henan & \(0.5389\)*** & \(3.49\) & \(0.002\) \\ Beijing & \(0.0116\) & \(0.01\) & \(0.988\) & Hubei & \(1.0109\)*** & \(7.59\) & \(0\) \\ Tianjin & \(0.2667\) & \(0.47\) & \(0.639\) & Hunan & \(0.3716\)*** & \(3.93\) & \(0\) \\ Hebei & \(0.0369\) & \(0.37\) & \(0.717\) & Guangdong & \(1.6016\)*** & \(6.49\) & \(0\) \\ Shanxi & \(-0.0098\) & \(-0.04\) & \(0.967\) & Guangdong & \(1.3158\)*** & \(6.42\) & \(0\) \\ Neimong & \(-0.3434\)** & \(-2.17\) & \(0.038\) & Chongqing & \(0.4646\) & \(1.24\) & \(0.226\) \\ Liaoning & \(-0.5244\) & \(-1.62\) & \(0.116\) & Sichuan & \(0.1397\) & \(0.71\) & \(0.482\) \\ Jilin & \(0.2894\)* & \(1.74\) & \(0.093\) & Guizhou & \(-0.2495\) & \(-0.65\) & \(0.519\) \\ Heilongjiang & \(0.15081\) & \(0.60\) & \(0.551\) & Yunnan & \(-0.1248\) & \(-0.54\) & \(0.591\) \\ Jiangsu & \(0.4037\)*** & \(4.58\) & \(0\) & Xizang & \(0.4568\) & \(0.60\) & \(0.553\) \\ Zhejiang & \(-0.1430\) & \(-0.45\) & \(0.658\) & Shaanxi & \(1.3516\)*** & \(5.46\) & \(0\) \\ Shanghai & \(-0.6491\) & \(-0.78\) & \(0.440\) & Gansu & \(-1.5196\)*** & \(-3.07\) & \(0.005\) \\ Fujian & \(0.6154\) & \(1.65\) & \(0.111\) & Qinghai & \(-0.3239\) & \(-0.43\) & \(0.673\) \\ Jiangxi & \(0.0258\) & \(0.11\) & \(0.910\) & Ningxia & \(0.1538\) & \(0.34\) & \(0.755\) \\ Shandong & \(-0.5529\)** & \(-2.39\) & \(0.024\) & Xinjiang & \(-1.1026\)*** & \(-3.16\) & \(0.004\) \\ \hline \end{tabular}
\end{table} 
Table 2: Individual effects. Figure 3: Estimated value and confidence interval of the first threshold of agricultural film use. In the individual effect results, Anhui is the basis for comparison. Its t statistics is \(-3.52\) and the \(p\) value is 0.001, which is less than 0.01. This research result indicates that the comprehensive factors such as soil, average temperature and average humidity have a significant impact on agricultural development. Compared with Anhui, the combined factors of soil, average temperature and average humidity in 12 provinces of Neimong, Jilin, Jiangsu, Shandong, Henan, Hubei, Hunan, Guangdong, Guangxi, Shaanxi, Gansu and Xinjiang had a significant impact on agricultural development. Compared with Anhui, the combined factors of soil, average temperature and average humidity in 17 provinces of Beijing, Tianjin, Hebei, Shanxi, Liaoning, Heilongjiang, Zhejiang, Shanghai, Fujian, Jiangxi, Chongqing, Sichuan, Guizhou, Yunnan, Xizang, Qinghai and Ningxia did not have a significant impact on agricultural development. With the use of agricultural film used as the threshold variable and the use of agricultural film, pesticide and fertilizer input used as the core variables, the regression is performed according to Formula (6). The regression results of a single threshold are shown in Table 3.  
The use of agricultural film is both a core variable and a threshold variable. When the use of agricultural film is below the threshold, every 1% increase in agricultural film usage will reduce agricultural output value by 0.9862% and the impact is significant. The main reason for this is that the use of agricultural film is less than the threshold value in Beijing, Tianjin, Shanghai and Guangdong between 2010 and 2021. Although these regions are in the eastern region and have rapid economic development, agriculture is not the main pillar industry that promotes their economic development. The economies of these regions are dominated by tertiary and secondary industries [66; 67]. The use of agricultural film in Qinghai in the western region showed an increasing trend from 2010 to 2021, but the use was not very large. When the use of agricultural film exceeds the threshold value, every 1% increase in agricultural film will increase agricultural output value by 1.1843% and the impact is significant. For most provinces in China, the promotion effect of agricultural film is very obvious.