## 3 Variables Description and Research Method
### The Threshold Effect Test of China's Agricultural Film Usage on Agricultural Development
The provinces where the use of agricultural film exceeds the threshold of 10.618 are shown in Figure 4. Figure 4 shows that the province with the highest agricultural film usage is Shandong. Although the use of agricultural film tended to decline from 2010 to 2021, the decline rate was relatively slow. Shandong has been a large source of agricultural production in China for many years, and its agricultural products are not only sold all over the country but also exported abroad in large quantities. The second province in the use of agricultural film is Xinjiang. From 2010 to 2021, the use of agricultural film in Xinjiang increased significantly. By 2021, it will almost reach the same level of Shandong. From 2010 to 2013, Henan ranked third in the use of agricultural film, but after 2013, Gansu surpassed Henan to become third. The use of agricultural film in Henan reached its highest \begin{table}
\begin{tabular}{c c c c c} \hline  & **Coef** & **Std. Err** & **t** & \(p>|t|\) \\ \hline LnAfu:1 (LnAfu \(\leq\) 10.618) & 0.9862 *** & 0.1078 & 9.15 & 0 \\ LnAfu:1 (LnAfu \(>\) 10.618) & 1.1843 *** & 0.1102 & 10.75 & 0 \\ LnPeu:1 (LnAfu \(\leq\) 10.618) & 0.0184 ** & 0.0079 & 2.33 & 0.02 \\ LnPeu:1 (LnAfu \(\leq\) 10.618) & 0.0320 *** & 0.0040 & 8 & 0 \\ LnFei:1 (LnAfu \(\leq\) 10.618) & \(-\)0.7738 *** & 0.1630 & \(-\)4.75 & 0 \\ LnFei:1 (LnAfu \(>\) 10.618) & \(-\)1.1107 *** & 0.1612 & \(-\)6.89 & 0 \\ \hline LnLai & 0.2979 * & 0.1592 & 1.87 & 0.062 \\ LnWri & 0.2368 *** & 0.0785 & 3.02 & 0.003 \\ LnTpm & 0.2425 *** & 0.0819 & 2.96 & 0.003 \\ \_cons & \(-\)6.4407 *** & 1.0806 & \(-\)5.96 & 0 \\ \hline \(R^{2}\) & 0.6879 & & & \\ F value & 55.84 & & & \\ Observations & 360 & & & \\ \hline \end{tabular} Notes. * is significant at the 0.1 level, ** is significant at the 0.05 level and *** is significant at the 0.01 level.  
\end{table} 
Table 3: Threshold model regression results of agricultural development as an explained variable. value in 2013 and then started to decline. However, its usage was in third place before 2013. After reaching the highest value in 2016, the use of agricultural plastic film in Gansu began to decline, and in 2019, it was lower than that of Henan. The use of agricultural film is used as the threshold variable. When the use of pesticides is used as the core variable, whether the use of agricultural film is below the threshold or above the threshold, the impact of pesticides on agricultural development is positive, but its impact is significant. Farmers will surely invest a lot of pesticides to promote the increase of agricultural products. China's agricultural economic growth is accompanied by a large number of pesticide applications [68], which will inevitably cause a large amount of pesticide residues. Once a large amount of residual pesticide enters the natural ecosystem, it will lead to a compromise in the quality and safety of agricultural products and damage the health of residents. Chemical fertilizer input is the core variable. When chemical fertilizer input is below the threshold, every 1% increase will decrease by 0.7738% in agricultural development, and the impact of chemical fertilizer input on agricultural development is significant. This is contrary to the findings of [PERSON] et al. [69]. Fertilizer inputs hinder agricultural development. When chemical fertilizer input crosses the threshold, every 1% increase in fertilizer input will reduce agricultural development by 1.1107%, and the impact of chemical fertilizer input on agricultural development is significant. The level of farmland nutrient management by Chinese farmers is low, and excessive application of chemical fertilizer is quite common [70]. However, less than 40% of fertilizer is absorbed and utilized by crops [71]. Excessive use of chemical fertilizers has led to the aggravation of water pollution and the degradation of cultivated land quality and ecosystem service functions. The result is a decline in crop yields, which has a negative impact on agricultural development.