| Phosphorus（P）is one of the seventeen essential plant nutrients in terms of plant growth and development,and its effectiveness has a significant impact on agricultural productivity.Long-term application of large amounts of chemical phosphorus fertilizer often leads to inefficient utilization of phosphorus fertilizer,phosphorus loss,and increased environmental risks.Soil texture is an important factor influencing the forms and effectiveness of soil phosphorus,which may result in differences in the occurrence of phosphorus forms and the risk of phosphorus loss.In order to study the effectiveness of phosphorus and the risk of phosphorus loss in soils of different textures（clay,loam,and sandy soil）,a long-term inorganic phosphorus fertilizer application experiment was conducted.The study analyzed the forms（organic and inorganic）and content of phosphorus in the soil,as well as the relationship and correlation between crop yield and the risk of phosphorus loss with phosphorus forms.Three typical soils in the middle and lower reaches of the Yangtze River were used in the experiment,with a total of 40 plots（2.5 m × 2.5 m）arranged randomly and separated by brick walls,including:（1）Silt soil along the river,classified as loam soil,with a total of 20 replicates;（2）Hilly horse liver soil,classified as clay soil,with a total of 10 replicates;（3）High sandy soil,classified as sandy soil,with a total of 10 replicates.Soil samples were collected after crop harvest for the determination of basic physicochemical properties and the study of phosphorus forms.The relationships between different forms of phosphorus in the soil were analyzed to understand the characteristics of phosphorus changes and phosphorus fertilizer transformation in typical soils under long-term fertilization.The aim was to provide a reference for the scientific management of soil phosphorus,improving phosphorus fertilizer utilization,and reducing environmental risks caused by phosphorus in agricultural production.The main conclusions of this study are as follows:（1）Significant differences in the physicochemical properties of the three soil textures were observed after long-term fertilization.The pH value and electrical conductivity（EC）of sandy soil were significantly higher than those of clay and loam soils（P<0.05）.In terms of pH,all three soils were classified as neutral to slightly alkaline.The organic matter（OM）and total nitrogen（TN）content in the three soil textures ranged from 11.8 to 23.8 g/kg and from 0.55 to 1.00 g/kg,respectively.Among them,loam soil had significantly higher levels of OM and TN compared to sandy soil（P<0.05）.The inorganic nitrogen content ranged from 9.0 to 29.3 mg/kg,with ammonium nitrogen（NH4+-N）being the dominant form.The inorganic nitrogen content in loam soil was significantly higher than that in sandy and clay soils（P<0.05）.The available potassium（AK）content ranged from 60.1 to 217.8 mg/kg,and the AK content in clay soil was significantly higher than that in loam and sandy soils（P<0.05）.The cation exchange capacity（CEC）ranged from 8.0 to 15.4 cmol（+）/kg,and the CEC of clay soil was significantly higher than that of loam and sandy soils（P<0.05）.Compared with the basic physical and chemical properties of the soil in 2015,the soil pH value of the three textures decreased,the AK content increased,and the organic matter content decreased in 2020.Under conditions of long-term chemical fertilizer application,the fertility level of clay and loam soils was higher than that of sandy soil.（2）Significant differences were observed in the forms and contents of phosphorus in the soil after 28 years of long-term inorganic phosphorus fertilizer application.The available phosphorus（Olsen-P）content ranged from 12.5 to 66.0 mg/kg,and the Olsen-P content in loam soil was significantly higher than that in clay and sandy soils（P<0.05）.In paddy fields,the Olsen-P content was significantly higher than in dryland（P<0.05）,and in the topsoil layer（0-20 cm）it was higher than in the subsoil layer（20-40 cm）（P<0.05）.The total phosphorus（TP）content ranged from 0.03%to 0.12%,and loam soil had significantly higher TP content than clay and sandy soils（P<0.05）.Except for clay soil,both sandy and loam soils were dominated by inorganic phosphorus（Pi）,accounting for 65.2%to 82.8%of the TP content.The organic phosphorus（Po）fractions in the three soil textures were mainly composed of moderately labile organic phosphorus（ML-OP）,with the lowest proportion of highly stable organic phosphorus（HR-OP）.In loam soil,the inorganic phosphorus content was mainly composed of Cas-P,Ca10-P,and O-P,while in clay and sandy soils,it was mainly composed of Ca8-P and Ca10-P.In terms of phosphorus nutrient content and forms,loam and clay soils had higher phosphorus levels compared to sandy soil.（3）After long-term fertilization,the effectiveness of phosphorus and its influencing factors differ among the three soil textures.The phosphorus activation coefficient（PAC）ranged from 3.2%to 10.0%,and it was significantly higher in paddy fields compared to dryland（P<0.05）.In the topsoil layer,clay soil showed a significantly higher PAC than loam and sandy soils（P<0.05）.Correlation analysis revealed that the available phosphorus content was significantly positively correlated with Ca2-P,Ca8-P,Ca10-P,Fe-P,and O-P,indicating that these forms were the most direct sources of available phosphorus.Soil texture was found to be an important factor affecting phosphorus availability.Fitting the phosphorus content with clay content showed that when clay content reached 18.4%,the theoretical maximum values of total and available phosphorus in the soil were achieved.Rice yield showed a significant increase（P<0.05）with the increase in available and total phosphorus content in the soil.（4）The risk of phosphorus loss was evaluated based on the contents of CaCl2-P and H2OP.The CaCl2-P content ranged from 0.02 to 0.72 mg/kg,and the H2O-P content ranged from 0.01 to 1.79 mg/kg.The loam soil showed a significantly higher content of CaCl2-P and H2OP compared to sandy and clay soils.Through fitting analysis,it was found that an effective phosphorus content of 30.0 mg/kg or a proportion of CaCl2-P to effective phosphorus of 0.6%can be considered as the critical point for phosphorus loss risk.Based on this critical point,the phosphorus loss risk was evaluated for soils of different textures.Clay soil was found to have minimal phosphorus loss risk,while loam and sandy soils showed some level of phosphorus loss risk.Both loam and sandy soils exhibited higher phosphorus loss risk during the wheat season compared to the rice season.Additionally,the phosphorus loss risk in the 20-40 cm soil layer during the rice season was higher than that in the 0-20 cm soil layer,whereas during the wheat season,the phosphorus loss risk was higher in the 0-20 cm soil layer. |
