Objective Effects of biochar combined with nitrogen fertilizer on the vertical migration of soil nutrients were studied to provide theoretical basis for improving soil quality under Phyllostachys violascens plantations.

Method The study object was P. violascens plantations, and the experiment was conducted from October 2020 to May 2021 in Fuyang District, Zhejiang Province. The experiment included nine treatments, three biochar levels (B0 0 t ha⁻¹, B1 10 t ha⁻¹, B2 30 t ha⁻¹) and three nitrogen fertilizer levels (N0 0 t ha⁻¹, N1 0.5 t ha⁻¹, N2 1 t ha⁻¹), B0N0, B0N1, B0N2, B1N0, B1N1, B1N2, B2N0, B2N1, B2N2. The vertical migration of soil nutrients and soil enzyme activities of P. violascens plantations were studied to provide a more comprehensive and precise scientific basis and guidance for the management under biochar combined with nitrogen fertilizer.

Result ① Biochar combined with nitrogen fertilizer increased soil nutrients. In the 0 ~ 15 cm soil layer, the combined application of low and high dosage biochar significantly increased soil total phosphorus, only biochar addition significantly increased soil available potassium, and the combined application of biochar significantly increased soil total nitrogen and available phosphorus. In 15 ~ 30 cm and 30 ~ 50 cm soil layer, biochar combined with nitrogen fertilizer significantly increased soil available potassium. In soil vertical direction, biochar alone or in combined with fertilizer both promoted nutrient transport in some extent. ② In the same soil layer, the activities of cellobiohydrolase, β-glucosidase, β-N-acetyl-glucosidase and leucine aminopeptidase kept constant or increasing with the amount of biochar or nitrogen application. The polyphenol oxidase activity was positively correlated with nitrogen addition dosage in 0 ~ 15 cm soil layer. ③ There was a correlation between soil nutrients and soil enzyme activities. Soil total nitrogen, soil total phosphorus and soil available potassium were significantly positively correlated with cellobiase, β-glucosidase, β-N-acetylglucosaminase and leucine aminopeptidase (P < 0.05), while soil organic carbon and soil available phosphorus were significantly negatively correlated with the above hydrolases (P < 0.05).

Conclusion  Appropriate amount of biochar combined with nitrogen fertilizer had significant positive effects on soil nutrients and enzymes. The change of soil enzyme activities caused by biochar combined with nitrogen fertilizer was the key factor for soil nutrient migration. Appropriate amount of biochar combined with nitrogen fertilizer was significant for improving soil available nutrients and soil enzyme activities under P. violascen plantation.