Abstract:

The aim of this study was to clarify the dynamic effects of Chinese milk vetch coupled with reduced chemical fertilizer on soil phosphorus adsorption and desorption characteristics in different years. This long-term field study was conducted in Xinyang， Henan province. The experimental design consisted of a control （no fertilizer， CK） and four treatments： fertilizer only （CF）， 22500 kg·ha^-1 Chinese milk vetch+80% fertilizer （G+80% CF）， 22500 kg·ha^-1 Chinese milk vetch+60% fertilizer （G+60% CF）， and 22500 kg·ha^-1 Chinese milk vetch+40% fertilizer （G+40% CF）. We determined the change trends of soil phosphorus adsorption and desorption characteristics， as well as their relationships with soil physicochemical properties in 2011， 2016， and 2020. The results showed that the Langmuir isothermal adsorption equation provided a good fit for the adsorption characteristics of soil phosphorus （R²=0.9804-0.9949， P<0.01）. The maximum phosphorus adsorption capacity （Q_max） of soil samples from the G+80% CF， G+60% CF， and G+40% CF treatments decreased from 2011 to 2020， whereas the phosphorus adsorption constant （K） and maximum phosphorus buffer capacity （MBC） increased over the same time period. Compared with their respective values in 2011， the Q_max of the G+80% CF， G+60% CF， and G+40% CF treatments had decreased by 11.30%， 12.95%， and 15.47%； K had increased by 20.73%， 22.50%， and 27.27%； and the MBChad increased by 8.63%， 6.43%， and 6.28% in 2020. In contrast， in the CF treatment， the Q_max of soil phosphorus increased with increasing age， whereas K and MBC decreased with increasing age. Compared with their respective values in 2011， the Q_max of soil phosphorus had increased by 8.80%， K had decreased by 12.20%， and MBC had decreased by 2.97% in 2020. In all treatments， the soil phosphorus adsorption saturation （DPS） did not show any consistent changes over the experimental period. The average desorption rate of soil phosphorus decreased during the experimental period in the CK and CF treatments， initially decreased and then increased in the G+80% CF and G+40% CF treatments， and showed a decreasing trend in the G+60% CF treatment. Compared with CK， the application of reduced chemical fertilizer coupled with Chinese milk vetch decreased the Q_max of soil phosphorus and increased the K， MBC， DPS， and average desorption rate of soil phosphorus in the same year. The results of correlation analysis showed that Q_max was significantly positively correlated with soil cation exchange capacity （CEC）， MBC was significantly negatively correlated with CEC， DPS was significantly positively correlated with alkali-hydrolyzed nitrogen （AN） and available phosphorus （AP）， and the desorption rate （DR） was significantly negatively correlated with available potassium （AK） and pH. The results of a redundancy analysis revealed that CEC， AP， and AK were the primary factors affecting soil phosphorus adsorption and desorption characteristics， with contribution rates of 26.7%， 18.5%， and 16.2%， respectively （P<0.05）. In summary， our results indicate that the adsorption and desorption of soil phosphorus are mainly affected by the soil CEC， AP， and AK. Long-term application of Chinese milk vetch coupled with reduced chemical fertilizer decreased P adsorption and increased P desorption in soil， while the long-term application of fertilizer alone had the opposite effect. Considering the adsorption and desorption characteristics of soil P and soil physical and chemical properties， the best effects were obtained by reducing chemical fertilizer usage by 20%-40% combined with 22500 kg·ha^-1 Chinese milk vetch. Our findings provide scientific guidance for reasonable fertilization in the rice-growing area of south Henan province.

Key words: soil phosphorus, adsorption and desorption, characteristic parameters, redundancy analysis