Effects of biochar application and irrigation rate on the soil phosphorus leaching risk of fluvisol profiles in open vegetable fields

Highlights: • A cascade extraction method was used to evaluate the soil P leaching risk from soil profiles in a field trial. • Biochar application increased soil leachable phosphorus, but it did affect the risk of phosphorus leaching. • Biochar application increased soil P leaching change point due to the biochar-induced increase in SOM. • Biochar application decreased soil P leaching risk due to the biochar-induced increase in the soil P leaching change point. • Biochar application combined with water-saving irrigation could be used as a measure for controlling soil P leaching. Biochar application was reported to influence soil phosphorus (P) leaching, but the reports are conflicting, and could be related to soil depth and water management. A field trial of a Wild Cabbage-Chinese Cabbage rotation was used to investigate the effect of biochar application and irrigation volume on P leaching risk in fluvisol soil profiles (0–20 cm, 20–50 cm, 50–100 cm) in the Chaobai River basin. The experiment included two biochar levels [0 (−BC), 30 t/hm² (+BC)], and two irrigation levels [conventional irrigation (CI) and water-saving irrigation (WSI)]. The irrigation rate of WSI was 80% of CI. The results demonstrated that there was no significant difference in soil leachable P in the soil profiles under the two irrigation volumes, while biochar application tended to increase soil leachable P in the top layer soil (0–20 cm) and subsurface layer soil (20–50 cm) irrespective of the irrigation rate. The average value of the P leaching "change point" in the soil profiles with +BC was significantly higher than that with −BC (0–20 cm: 35.52 mg kg⁻¹ vs. 25.86 mg kg⁻¹; 20–50 cm: 27.61 mg kg⁻¹ vs. 20.02 mg kg⁻¹). Additionally, the P leaching risk was observed in all top layer soil (0–20 cm) irrespective of irrigation rate and biochar application, and the P leaching risk in the subsurface layer (20–50 cm) with +BC was lower than that with −BC, especially under WSI. Therefore, it is recommended that biochar application combined with water-saving irrigation could be used as a measure for controlling soil phosphorus leaching under open field vegetable rotation in the alluvial soil of Chaobai River basin.