## 1 Introduction  
Phosphorus is an essential element for life, which constitutes many biomolecules and participates in important life activities such as photosynthesis and respiration [1]. It plays a significant role in material exchange and circulation throughout the entire biosphere. It is widely believed that phosphorus availability is optimal under near-neutral conditions [2]. In acidic environments, phosphorus strongly binds cations such as Fe\({}^{3+}\) and Al\({}^{3+}\), while in alkaline environments, it combines with Ca\({}^{2+}\) to form insoluble salts, both of which hinder plant uptake. Phosphorus in acidic soil is prone to forming insoluble phosphates due to the actions of ion adsorption and coordination adsorption, which can lead to its fixation in the soil phosphorus pool or retention by microorganisms [3; 4]. Therefore, most soils face the problem of a low available phosphorus content, which leads to phosphorus deficiency in crops and results in low yields [5; 6; 7]. The situation of a soil phosphorus deficiency and low utilization rate of phosphorus fertilizer has led to the fact that significant increases in grain production are always accompanied by substantial inputs of phosphorus fertilizer. This not only results in the wastage of limited phosphorus fertilizer resources but also inevitably leads to an increase in phosphorus concentrations in farmland runoff, which can easily cause eutrophication and other environmental problems [8; 9]. Camellia Oleifera (CO) is an evergreen shrub belonging to the genus _Camellia_ in the family _Theacae_. It is rich in fatty acids and special nutrients such as squalene. In Guizhou, China, CO has been cultivated for hundreds of years. Not only are its fruits used as raw materials for tea oil production, but its leaves also hold certain economic value and strategic significance. This has brought considerable economic benefits to local CO growers and provided pathways and channels for rural economic development [10]. For CO, phosphorus deficiency can lead to a variety of problems of different degrees, such as slow growth, a dark green or bronze leaf color, poor root development, weakened stress resistance, a reduced oil content in fruits, and changes in flavor and quality. Therefore, it is particularly important to seek more efficient phosphorus supply methods in the production process of crops such as CO [11]. Biogas slurry is typically produced through the anaerobic fermentation of organic materials such as manure, kitchen waste, and straw. It is rich in plant growth hormones, including amino acids, indoleacetic acid, and gibberellins. Most of the raw materials for biogas slurry come from livestock and poultry farms. In the past, advanced processes and high costs were often required to safely treat these animal wastes. However, more people now opt for anaerobic fermentation combined with other additives to produce biogas fertilizer, which not only reduces the volume of solid waste but also effectively recycles resources [12]. Swamp fertilizers have always been an important source of nutrients for cultivated soils in China, especially with the rapid development of animal husbandry in recent years. Dung and urine resources from large-scale breeding have made the practice of returning biogas slurry to fields more common [13]. In recent years, as the awareness of environmental protection and green development has increased, research and practical applications concerning the replacement of chemical fertilizers with biogas slurry and its impact on soil microorganisms have received widespread attention. Studies have found that returning biogas slurry to fields can increase wheat yields [14], improve soil quality, and promote the growth of corn and ryegrass [15]. The combined application of biogas slurry and chemical fertilizers can enhance soil fertility, increase tomato yield [16], and effectively increase the yield of CO fruits [17].