## 2 Materials and Methods
### Research Hypotheses
#### 2.1.1 The Spatial Spillover Effect of Environmental Regulation on Agricultural Green Development
Additionally, with subsidies for delayed fertilization control, soil testing and formula fertilization, and R&D of energy-saving and environmental protection machinery technology, agricultural carbon emissions could be reduced, as well as the adjacent regions due to technology spillovers [22]. On the other hand, financial support for agriculture could promote competition in agricultural development industries between local and adjacent regions, which would increase agricultural carbon emission and inhibit agricultural green development by a high input of energy, fertilizers, pesticides, untreated agricultural wastewater containing nitrogen and phosphorus and other agricultural materials [5; 6; 7; 8; 9; 10; 11; 12; 13; 14; 15; 16; 17; 18; 19; 20; 21; 22; 23]. Furthermore, one region would gather more agricultural production resources which may have a siphoning effect on the adjacent regions, suppressing the adjacent regions' level of agricultural green development [23]. Thus, this paper puts forward the following hypothesis:  
**Hypothesis 2 (H2)**. _Financial support for agriculture has a spatial spillover effect on agricultural green development_. 2.1.3. The Spatial Spillover Effect of Interaction between Environmental Regulation and Financial Support for Agriculture on Agricultural Green Development  
Interaction between environmental regulation and financial support for agriculture on agricultural green development has been focused, which could be included the following two aspects. First, agricultural pollution governance investment and rural pollution control investment are proposed to be integrated into an index of agricultural ecological pollution control investment [24; 25]. Second, suggestions for agricultural green development mainly include two aspects of environmental regulation and financial support for agriculture, such as rational intensity of fertilizer application, rewards for public participation in environmental regulation, agricultural green development funds and agricultural machinery input [5; 6]. In addition, research also shows that the interaction between environmental regulation and financial support for agriculture has a spatial correlation with agricultural green development. First, local government would increase financial protection and economic expenditure on the regional agricultural environment. While adjacent regions could take advantage of geographical location to realize free riding on the environmental governance performance and then promote their agricultural green development. Second, excessive government funds to support agriculture would lead to local protection of environmental protection performance, which would hinder element flow with their adjacent regions, leading to negative externalities of environmental regulation, and then have a negative impact on the agricultural environment of adjacent regions. Flexible policy instruments are essential for ecological restoration [21]. Thus, this paper puts forward the following hypothesis:  
**Hypothesis 3 (H3)**. : _Interaction between environmental regulation and financial support for agriculture has a negative spatial effect on agricultural green development._  
In conclusion, previous studies only pay attention to the single spatial spillover effect of environmental regulation and financial support for agriculture on agricultural green development, and only suggestion that environmental regulation and financial support for agriculture should be combined to promote agricultural green development has been proposed. As such, the spatial spillover effect of the interaction between environmental regulation and financial support for agriculture on agricultural green development should be explored from the empirical perspective.