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

Abstract 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.