Abstract:
Objectives This study aimed to investigate the effect of phosphorus (P) fertilization on soil soluble P extracted by CaCl2 solution (CaCl2-P) in fluvo-aquic soils with different available P (Olsen-P) content and evaluate the leaching risk of soil P, in order to provide the theoretical reference on rational utilization of nutrients, reduction of chemical P fertilizer application and P loss from fluvo-aquic soils.
Methods Five treatments with different Olsen-P content (0.8, 12.5, 25.7, 44.7, 56.4 mg/kg, here after referred as OP1, OP2, OP3, OP4, and OP5) from a long-term monitoring experiment were selected, and five rates of P fertilizer (F0, F1, F2, F3, and F4) were applied for each treatment. Micro-plots with random block design were established and a double cropping system was adopted in the experiment with both winter wheat and summer maize crops grown sequentially in every cropping year. After harvesting, soil samples were collected. Soil Olsen-P and CaCl2-P contents were measured and the relationship between Olsen-P and CaCl2-P was established.
Results Soil CaCl2-P content was in the range of 0.07−2.68 mg/kg, accounting for 0.5%−5.6% of the soil Olsen-P. High amount of P fertilization in the short term significantly enhanced soil Olsen-P and CaCl2-P. However, the increment of Olsen-P and CaCl2-P was not synchronous. When soil Olsen-P was lower than 28.0 mg/kg, the ratio of CaCl2-P/Olsen-P decreased with the increase of Olsen-P, while the ratio of CaCl2-P/Olsen-P increased rapidly after soil Olsen-P was increased to 28.0 mg/kg, indicating that P fertilizer increased soil Olsen-P first and CaCl2-P increased rapidly after Olsen-P was increased to a certain level. The relationship between CaCl2-P and Olsen-P was fitted well with line-line model, with the change-point of 30.2 mg/kg for Olsen-P and 0.3 mg/kg for CaCl2-P, indicating that soil P leaching loss risk increased when soil Olsen-P was higher than 30.2 mg/kg.
Conclusions High amount of P application improved soil CaCl2-P content, which on one hand facilitated the P uptake of crops, but on the other hand increased the leaching loss risk of soil P. In the study area, the soil P leaching loss threshold was 30.2 mg/kg. Soil Olsen-P content was higher than 30.2 mg/kg in more than 50% of plots in the microplot experiment. Therefore, scientific application and management of P fertilizer should be strengthened to decrease the leaching loss risk of soil P.