# Effects of Long-Term Fertilization on Phosphorus Form and Availability in Black Soil
## 4 Discussion
This pairing could facilitate the conversion from di- to mono-orthophosphate, suggesting that the application of organic fertilizers increases the potential soil P bioavailability [36]. The distribution of organic fertilizers can enhance phosphorus effectiveness by promoting processes such as phosphate dissolution and organic phosphorus mineralization in many ways [37]. In soils with a low inorganic phosphorus content and a high phosphorus fixation capacity, a significant portion of the phosphorus absorbed by plants comes from the mineralization of organic phosphorus. Organic phosphorus in the soil undergoes mineralization before it can be used as a resource available or potentially available to crops [38]. Adding organic fertilizers can provide a carbon source for microorganisms to improve the activity of soil alkaline phosphatase, which promotes the mineralization of organic phosphorus [39]. Organic phosphorus originates from an organic process that precisely hydrolyzes orthophosphate diesters into orthophosphate monoester and orthophosphate monoester into inorganic orthophosphate, and phosphorus in organic fertilizers mainly exists in the form of Po, which is easily enzymatically cleaved in soil [40]. Soil C/P ratio affects Po organic phosphorus. When the C/P ratio is less than 200, Po is easily mineralized. The C/P ratio in organic manure is generally lower than 50, and most of the Po in the manure applied to the soil is easily converted to Pi [34]. According to [PERSON] et al. [41], the presence of phosphorus fertilizer in the manure has a greater effect on the content of organic phosphorus monoester-Po in the soil, and the content of monoester-Po increases with the increase in the amount of phosphorus fertilizer applied. The results of this study showed that the CK treatment had a higher proportion of monoesters and diesters, which may be due to the long-term application of chemical and organic fertilizers promoting the transformation of phosphorus into different forms in the soil. The correlation between total phosphorus and inorganic phosphorus in the different forms of phosphorus was significant, and inorganic phosphorus was more easily absorbed by plants than organic phosphorus, which may contribute to the main reason behind this correlation. [PERSON] [42] found that the correlation coefficient between soil effective phosphorus and water-soluble phosphorus was the largest and considered soil water-soluble phosphorus to be the most effective source of phosphorus for plants, a result that is different from the results of the present experiments. This difference may be because water-soluble phosphorus is easily absorbed by plants or quickly utilized by microorganisms. Moderately and mildly active phosphorus still showed a significant correlation with soil effective phosphorus, indicating that if the content of effective phosphorus in the soil decreases, the soil can improve the effectiveness of phosphorus through the activation of insoluble phosphorus. This means that it is effective for plants for a long period of time, further proving that the various forms of phosphorus can be converted into each other to improve the effectiveness of phosphorus. A certain correlation exists between the phosphorus forms obtained by continuous leaching and the phosphorus forms identified using solution \({}^{31}\)P NMR spectroscopy (Figure 5). Orthophosphate is more closely related to partially activated phosphorus, moderately activated phosphorus, and mildly activated phosphorus, and the correlation between pyrophosphate and phosphoric acid dieser is higher. Other scholars have found that pyrophosphate also has a certain correlation with phosphate monoesters [43]. [PERSON] et al. [44] concluded that a small portion of phosphate diesters can be rapidly degraded into orthophosphate monoesters in alkaline extracts, and thus, a significant positive correlation may exist between the two.