Effects of biochar addition on soil phosphorus composition and transformation in Eucalyptus plantation

Abstract

In order to improve the phosphorus(P)deficiency in the soil of Eucalyptus plantations in subtropical China, we used biochar(BC)as a soil amendment to investigate the soil of Eucalyptus plantations(15 years old). Meanwhile, we added the different amounts [0(CK), 2%, 5%, 10% and 20%] of BC through the laboratory culture experiment to evaluate the effects of different amounts of BC on P components and transformation in soil and its relationship with soil physicochemical properties. The results were as follows:(1)Compared to CK, the nitrate nitrogen(NO3--N), total phosphorus(TP), microbial biomass phosphorus(MBP)and pH values were significantly increased at 20% BC addition, respectively(P<0.05), the MBP and pH values were significantly increased at 2%, 5%, and 10% BC addition, respectively(P<0.05), while no marked difference was found in other soil physicochemical properties.(2)Compared to CK, the labile P(LP)was significantly increased at 2% of BC addition(P<0.05), the available P(AP)and LP were significantly increased at 5% and 10% of BC additions, respectively(P<0.05). Moreover, the AP, LP and occluded P(OP)were significantly increased at 20% BC addition(P<0.05), whereas the moderately available P(MP)had no significant change under the four BC additions.(3)The total activities of β-glucosidase(BG), β-N-acetylglucosaminidase(NAG), L-leucine aminopeptidase(LAP), and acid phosphatase(ACP)involved in C, N and P transformations increased significantly at 10% and 20% BC additions than those in CK(P<0.05).(4)Correlation analysis showed that ln(BG)and ln(NAG+LAP)were positively correlated with ln(ACP), respectively(P<0.05). In addition, redundancy analysis(RDA)indicated that pH, TN and TP appeared to be the primary drivers of variations in soil P components of Eucalyptus plantations. Furthermore, structural equation model(SEM)revealed that the pH, C:P and N:P of soil were the most critical factors driving P transformation. In conclusion, our findings suggest that different amounts of BC improve the enzyme activities related to C, N cyclings by affecting soil physicochemical properties and improving the P supply potential of soil in Eucalyptus plantations. Notably, 20% BC addition had the optimum effect. This study provides critical theoretical guidance for gaining knowledge on soil nutrient management in Eucalyptus plantations and facilitating the sustainable development of forests in subtropical China.

Keywords

• biochar
• eucalyptus plantation
• soil phosphorus component
• soil enzyme activity