Objectives There are high accumulation of P and high risk of P migration in greenhouse vegetable systems. Hydrotalcite-modified biochar is a good anion adsorption material, we investigated the effects of hydrotalcite-modified biochar prepared from different materials on P adsorption capacity in high-phosphorus greenhouse vegetable fields. The results will provide a scientific basis for optimized utilization of modified biochar to reduce the risk of P loss in high-phosphorus greenhouse vegetable fields.

Methods Bamboo biochar (BB), corn straw biochar (MB), and pig manure biochar (PB) were prepared by limited oxygen pyrolysis at 500℃. Zn/Fe hydrotalcite (Zn/Fe LDHs) was loaded on three biochar surfaces by co-precipitation method to obtain hydrotalcite-modified bamboo biochar (LDH-BB), hydrotalcite-modified corn straw biochar (LDH-MB) and hydrotalcite-modified pig manure biochar (LDH-PB). Six biochar samples were used as experiment materials for soil phosphorus adsorption-desorption experiment and soil column leaching experiment, and the treatment without biochar was used as the control. Langmuir and Freundlich equations were used to fit the adsorption data. Phosphorus desorption capacity of soil-biochar mixture was determined after phosphorus adsorption. Soil column leaching experiment was conducted to determine volume, pH, and content of different phosphorus fractions of leaching solution.

Results The contents of Zn, Fe, O/C and (O + N) /C atomic ratio of biochar were increased by modification, and pH value, contents of C, N and P were decreased. After modification, irregular layered attachments appeared on the surface of biochar and the specific surface area increased in the order of LDH-BB >LDH-PB>LDH-MB>BB>MB>PB. According to the fitting results of Langmuir equation, LDH-BB treatment had the best phosphorus adsorption performance, and its maximum theoretical adsorption capacity (3681 mg/kg) was 3.41, 3.34 and 4.25 times that of LDH-MB, BB and MB treatment, respectively. The soil column leaching experiment revealed that the volume of leaching solution in each biochar-amended treatment decreased compared with that of CK, and the volume of cumulative leaching solution was the least in LDH-BB treatment, and the reduction was 1.61, 3.27, 4.32, 1.89, and 2.59 times that in BB, MB, PB, LDH-MB and LDH-PB treatments, respectively. The cumulative phosphorus leaching amount (TP) in LDH-BB, LDH-MB and LDH-PB treatments was significantly reduced by 25.68%, 17.51%, and 34.38% compared with BB, MB, and PB treatments, respectively. For all treatments, the proportion of soluble reactive phosphorus (SRP) was the highest, followed by soluble organic phosphorus (SOP) and particulate phosphorus (PP). Compared with BB, MB and PB treatments, the proportion of SRP in leaching solution was significantly reduced by 7.72%, 6.69%, and 12.07% in LDH-BB, LDH-MB and LDH-PB treatments, respectively.

Conclusions The addition of Zn/Fe hydrotalcite-modified bamboo biochar significantly increased the phosphorus adsorption capacity and reduced the phosphorus cumulative leaching capacity in greenhouse vegetable soil, which was an effective measure to reduce the risk of phosphorus loss in high-phosphorus greenhouse vegetable systems.