关键词: 黑土, 有效磷, 农学阈值, 环境阈值, 磷形态, 土壤化学性质

Abstract:

【Objective】 Agronomic and environmental thresholds of Olsen phosphorus (P) are the most important parameters for soil P management, but the characteristics of phosphorus fractions under the different threshold regions are not clear. This research evaluated the characteristics of the P fraction under the different threshold regions of Olsen P and its influencing factors in black soils for enabling to understand the transformation process of soil P, so as to provide a reference for optimizing the Olsen-P management strategy and improving the efficiency of P resource utilization.【Method】9 Olsen P levels (11, 21, 31, 40, 57, 69, 128, 331, and 490 mg·kg^-1) of agricultural fields plow layer (0-20 cm) soil samples were collected in Gongzhuling, Jilin Province. TIESSEN-Moir modified HEDLEY phosphorus classification method was used to classify soil inorganic phosphorus and organic phosphorus. The relationship between the phosphorus fractions and soil chemical properties, such as soil organic matter (SOM), C/P, Fe, and Al oxides, was also analyzed to clarify the characteristics of phosphorus fractions and the main controlling factors under the different threshold regions of soil Olsen P.【Result】The P pool was dominated by Pi, accounting for 71.25%-96.19%, with Po accounting for 3.81%-28.75%. When the Olsen P level was below the agronomic threshold (7.4-13 mg·kg^-1), the proportion of liable P (LP) of 19.89% was the lowest in comparation with other P fractions. When the Olsen P level was below the environmental threshold (51.0-56.4 mg·kg^-1), the proportion of medium active phosphorus (ML-P) and stable phosphorus (OP) is close, 36.03% and 35.49% respectively, both higher than the proportion of LP (28.48%). The highest proportion of LP (42.86%) was observed when the Olsen P level was above the environmental threshold. When the Olsen P level is higher than the environmental threshold, the content of LP and ML-P in the soil is significantly higher than that in the soil where the Olsen P level is lower than the environmental threshold, and the resin-P showed the greatest variation with Olsen P above and below the environmental threshold. The value of P activation coefficient (PAC), and the concentration of Mehlich-3 extractable aluminum (M3-Al), free Al oxide (Ald), organic-bound Fe, Al oxide (Fep, Alp), and amorphous Fe, Al oxide (Feo, Alo) increased significantly, while a significant decrease in C/P was observed with increasing Olsen P levels. The correlation analysis shows that when the Olsen P level was below the environmental threshold, the soil organic matter was positively and significantly correlated with the highly active inorganic P fractions (Resin-P, NaHCO₃-Pi, NaOH-Pi) above the environmental threshold; when the Olsen P level was above the environmental threshold, Fep+Alp showed a strong positive correlation with each inorganic P fraction blow the environmental threshold. The redundancy analysis results showed that when the Olsen P level was below the environmental threshold, SOM and M3-Fe were the key factors for affecting the change of P fractions in black soils, explaining 50.2% and 24.1% of the total variation, respectively; when the Olsen P level was above the environmental threshold, Fep+Alp was the main factor influencing the change of P fractions, explaining 68.1% of the total variation.【Conclusion】 When the Olsen P level was below the agronomic threshold, the liable P accounted for the lowest proportion; however, which was the greatest proportion when the Olsen P level was above the environmental threshold. In addition, the Resin-P is the phosphorus fraction with the largest variation below and above the environmental threshold. SOM, M3-Fe, and Fep+Alp were the key factors affecting the change of P fractions below and above the environmental threshold, respectively.

Key words: black soil, available phosphorus, agronomic threshold, environmental threshold, phosphorus fractions, soil chemical properties