## 4 Discussion
### Characterization of Nutrient Variation and Recommendations for Zoning Management
This suggests a lower general dispersal and a shift from fragmentation to uniformity in their dispersion. Both total nitrogen and organic matter critically impact crop yields [39]. Their concentrations are intrinsically linked to land use approaches, soil classifications, and the introduction of organic fertilizers [40; 41]. In regions with diminished levels of organic matter, total nitrogen, and alkali-hydrolyzable nitrogen, adopting practices like straw return [42], deep filling [43], organic crop rotation [44], and intercropping [45] can markedly elevate the soil's organic matter and nitrogen content. In Fengtai County, the soil's available phosphorus block ratio stands at 85.6% over a range of 756 m. This infers that the spatial fluctuations of available phosphorus across extensive areas predominantly stem from unpredictable elements like human actions and fertilization techniques. Both its global Moran's I index of 0.884 and coefficient of variation at 59.12% surpass other nutrient benchmarks considerably. Its spatial autocorrelation is also statistically significant (Z > 2.58), suggesting a robust aggregation trend for available phosphorus. The LISA clustering diagram reveals noticeable clusters of high and low values of available phosphorus. The northeastern sector showcases a dense high-value cluster, while the central-southern zone predominantly displays lower values. This might be due to intensified urbanization in the east, where human actions are more condensed, resulting in available phosphorus accumulation. For northeastern sectors with abundant available phosphorus, field checks are imperative to identify the cause of its heightened levels. Proactive, scientifically backed measures are crucial to avert potential agricultural runoff pollution. Conversely, in the central-southern regions with diminished phosphorus, it is advisable to employ methodical fertilization strategies, like applying foliar phosphorus [46], integrating organic fertilizers with phosphorus supplements [47], and leveraging traditional zinc fertilizers to bolster soil phosphorus efficiency [46]. As for Fengtai County's soil-available potassium, its block ratio is 71.8% spanning a range of 199 m. This highlights that small-scale spatial fluctuations of available potassium are shaped by both unpredictable aspects, such as human interactions, and structural components like the formation of the parent material. Its global Moran's I index sits at 0.562, indicating a more decentralized spatial distribution than other nutrient metrics. This could be attributed to individual farmer practices, which disrupt uniform filling and fertilization approaches, leading to a patchy distribution of available potassium in certain zones. Slow-release potassium exhibits a block ratio of 97.3% across 237 m, suggesting that its minor spatial inconsistencies are mainly steered by unforeseen factors like human interventions. Its global Moran's I index of 0.729 indicates a denser spatial spread. Using the LISA clustering diagram as a reference, regions with elevated slow-release potassium are more clustered, while low-value areas appear sporadic. This pattern might correlate with the variety of crops cultivated. As crops utilize available potassium, leading to its shortfall, the soil's slow-release potassium transforms into available potassium to maintain a balance [48]. For zones with potassium scarcity, implementing practices like standard straw reintroduction to plots and judicious potassium fertilizer applications can notably enhance soil potassium concentration [49].