The inhibiting effects of biochar-derived organic materials on rice production.

The effects of PBC and HBC on rice production, NUE and corresponding mechanisms were examined. Six treatments, P05, P30, H05, H30 (P: PBC; H: HBC; 05 and 30 represented the application rate of 0.5 and 3.0% w/w), CKU (urea application without char) and CK (no application of char and urea), were set up. Results showed that P05, P30 and H05 increased grain yield by 1.8-7.3% (P > 0.05), whereas H30 reduced grain yield by 60.4% (P < 0.05), compared to CKU. Meanwhile, HI under P05, P30 and H05 increased by 3.4-3.6%, while H30 decreased by 9.1% (P < 0.05). NUE and NAE showed similar trends with rice yield. By investigation, the excessive introduction of BDOM plays a crucial role in the reduction of rice production and NUE under higher HBC application. GC-MS/MS analysis showed that the soluble BDOM of HBC and PBC was quite different, and compounds such as 2,6-dimethoxyphenol might stress rice growth. ESI-FT-ICR-MS analysis showed that the BDOM of HBC contained a certain quantity of aromatic compounds, which may also stress rice growth. Overall, HBC pretreatment should be conducted, and the application rate should be strictly controlled before its agricultural application.