## 4 Inventory and Analysis
### Analysis of Rooftop Agricultural Production Potential in Shibei District
#### 4.2.1 Determine the Annual Yield per Unit Area of Vegetables under Different Cultivation Methods  
According to national statistical data, the unit area yield of vegetables in China in 2016 was 3.57 kg/m\({}^{2}\)[19]. The total vegetable production was 798 million tons, of which the facility vegetable production (excluding fruits and melons) was 252 million tons, with a unit area yield of 6.44 kg/m\({}^{2}\). The yield of soil-cultivated vegetables was 546 million tons, with a unit area yield of 2.97 kg/m\({}^{2}\). In addition, differences in planting varieties, regions, and facilities also result in significant differences in annual yield per square meter. For example, the average annual yield of greenhouse tomatoes in China can reach 10-15 kg/m\({}^{2}\), and cucumbers can reach 15-20 kg/m\({}^{2}\), which is significantly higher than other vegetables. Foreign glass greenhouse tomatoes have a yield of up to 40-80 kg per square meter, and they are at a leading level in variety selection, cultivation techniques, environmental regulation, and other aspects. China's facility horticulture is still mainly produced and operated by individual farmers, with a relatively low level of industrialization. Another study pointed out that China has the world's largest facility agriculture area, with over 90% of it engaged in vegetable production, but the average annual yield of greenhouse vegetables is only about 9 kg/m\({}^{2}\). From the above various data, it can be seen that the yield of facility cultivation is significantly better than that of soil cultivation, but there is no quantitative standard for vegetable yield per unit area under different greenhouse types, planting varieties, and technical conditions. The introduction of facility agriculture in urban areas in the future will help increase urban vegetable production and enrich urban vegetable varieties. Table 4 shows the relevant data of some examples of facility cultivation and soil cultivation. By analyzing and weighting these data, the reference standards for annual yield per unit area of soil cultivation and facility cultivation were obtained in order to improve the reliability and accuracy of the reference data as much as possible and reduce the calculation error of total vegetable yield. The numerical values of vegetable yield from national and some practical cases are cited here without citing the local vegetable yield data in Qingdao. This is because the vegetable yield per unit area is not only affected by the planting area but also by various factors such as planting varieties and facilities. In addition, there are no reliable data on roof agriculture planting in Qingdao, so it is not possible to comprehensively consider various factors. In this case, using the current actual vegetable production in China as the \begin{table}
\begin{tabular}{c c c c c c c} \hline
**Building** & **Roof** & **Suitability** & **Proportion** & & & \\
**Type** & **Area S (ha)** & & **Level** & **of Area** & **Quantity (Pieces)** & **Area (ha)** \\ \hline Residential & \(15\leq S<500\) & 85.60 & Level 3 & 22.33\% & 2781 & & \\ buildings & \(500<S<5000\) & 167.7 & Level 2 & 43.76\% & 2078 & 4859 & 253.3 \\ Other types & \(15\leq S\leq 5000\) & 11.7 & Level 3 & 3.05\% & 403 & & \\ of buildings & \(500<S<5000\) & 94.4 & Level 2 & 24.63\% & 708 & 1138 & 130.0 \\  & \(5000\leq S\) & 23.9 & Level 1 & 6.24\% & 27 & & \\  & \multicolumn{3}{c}{Total} & & & 5997 & 383.3 \\ \hline \end{tabular}
\end{table} 
Table 3: Inventory results of available roofs in the Shibei District of Qingdao (classification by suitability level). main reference enabled the obtained data to be applied in the calculation of potential in more regions. However, it should be noted that in order to reduce errors in the calculation of agricultural production potential in a certain region, production data from the same climate zone, planting facilities, and varieties should be referred to as much as possible.