## 5 Discussion  
### Factor Analysis of Changes in Crop Rotation Patterns  
The analysis of cropping patterns for sesame, oats, and potato from 2019 to 2023 revealed that crop rotation comprised a higher proportion of the planting system than \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Pattern in Cropping System** & **Crop Rotation** & **2019–2020** & **2020–2021** & **2021–2022** & **2022–2023** & **Average** \\ \hline \multirow{4}{*}{Potato-dominated} & P-P & 31.86 & 33.40 & 27.97 & 32.54 & 31.44 \\  & P-O & 12.23 & 8.64 & 11.22 & 10.43 & 10.63 \\  & P-M & 20.56 & 9.18 & 17.53 & 12.30 & 14.89 \\  & P-S & 1.38 & 2.45 & 1.32 & 1.30 & 1.61 \\  & P-OC & 33.96 & 46.33 & 41.95 & 43.43 & 41.42 \\ \hline \multirow{4}{*}{Oats-dominated} & O-P & 7.12 & 10.58 & 6.83 & 10.75 & 8.82 \\  & O-O & 40.63 & 30.59 & 21.79 & 40.78 & 33.45 \\  & O-M & 25.66 & 6.26 & 12.21 & 12.64 & 14.19 \\  & O-S & 1.10 & 3.11 & 1.80 & 1.52 & 1.88 \\  & O-OC & 25.49 & 49.45 & 57.37 & 34.3 & 41.65 \\ \hline \multirow{4}{*}{Maize-dominated} & M-P & 3.11 & 4.91 & 2.44 & 2.57 & 3.26 \\  & M-O & 5.48 & 5.61 & 3.10 & 5.43 & 4.91 \\  & M-M & 77.4 & 60.20 & 78.11 & 75.56 & 72.82 \\  & M-S & 0.86 & 1.45 & 1.03 & 1.15 & 1.12 \\  & M-OC & 13.15 & 27.82 & 15.32 & 15.3 & 17.90 \\ \hline \multirow{4}{*}{Sesame-dominated} & S-P & 5.19 & 7.67 & 6.36 & 5.07 & 6.07 \\  & S-O & 20.67 & 9.72 & 7.30 & 12.92 & 12.65 \\ \cline{1-1}  & S-M & 27.31 & 11.1 & 14.36 & 16.95 & 17.43 \\ \cline{1-1}  & S-S & 4.79 & 5.60 & 3.50 & 9.39 & 5.82 \\ \cline{1-1}  & S-OC & 42.03 & 65.91 & 68.47 & 55.67 & 58.02 \\ \hline \multirow{4}{*}{Other crops-dominated} & OC-P & 4.73 & 6.25 & 4.29 & 3.93 & 4.80 \\ \cline{1-1}  & OC-O & 7.95 & 5.20 & 4.53 & 9.43 & 6.78 \\ \cline{1-1}  & OC-M & 14.42 & 5.69 & 9.08 & 10.64 & 9.96 \\ \cline{1-1}  & OC-S & 1.87 & 2.11 & 1.16 & 1.48 & 1.66 \\ \cline{1-1}  & OC-OC & 71.03 & 80.74 & 80.95 & 74.53 & 76.81 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Major crop rotation patterns in the study area (2019–2023) based on field area proportions (unit: %). P, O, M, S, OC represent potato, oat, maize, sesame and other crops, respectively. Figure 9: Sankey diagram illustrating crop rotation dynamics for major crop types in Zhangjiakou from 2019 to 2023.  
monocropping, with maize predominantly grown as a monocrop and significant annual variations in crop area proportions (Figures 7-9). The underlying reasons can be attributed to several factors:  
Groundwater over-extraction and irrigation water scarcity in the FPEC significantly influence crop planting patterns, particularly in northern Zhangjiakou. The region's arid conditions compel farmers to adopt crop rotation strategies as an effective means to optimize limited water resources and enhance soil moisture retention and fertility. Consequently, crop rotation emerges as an essential practice to alleviate pressure on scarce water resources and sustain long-term agricultural productivity. Additionally, crop rotation helps prevent soil degradation and nutrient depletion, which are prevalent issues in continuous monoculture systems, thus contributing to long-term agricultural stability [62]. Economic factors, including market supply and demand, crop prices, and profitability, directly influence farmers' planting decisions. For example, in regions such as Kangbao, Guyuan, and Zhangbei, farmers frequently shift from staple crops (potato, maize, oats, and sesame) to economically profitable vegetables (cabbage, celery, beans, zucchini, peppers, onions) based on market-driven incentives [33; 63]. The higher demand and more favorable prices of vegetables stimulate substantial annual fluctuations in cropping patterns, especially influencing the proportion of oats, potato, and other crops. Furthermore, initiatives by the Chinese Government aimed at improving water conservation and irrigation efficiency have further reshaped regional cropping structures.