化肥配施生物炭对稻田田面水氮磷流失风险影响

在控制外源氮输入相同的前提下,通过大田试验研究生物炭部分替代化肥作为底肥,不同生物炭施用量(5、10、20 t·hm~(-2))对水稻生长期内稻田田面水氮磷迁移转化特征的影响。研究结果表明:各处理的田面水总氮、硝氮、铵氮浓度在施肥后第3 d达到最高,然后迅速下降,并逐渐稳定;田面水总磷浓度在施肥后2~4 d内增幅较小,而后迅速下降至稳定,施加生物炭对田面水总磷的影响不大;可溶性磷浓度在施肥后2~4 d内处于平稳下降的状态,之后迅速下降至稳定。稻田施肥后10 d内是控制氮磷流失的最佳时段。采用生物炭代替部分化肥的施肥方式,在一定范围内能降低稻田田面水的氮磷浓度,稻田退水氮、磷的输出负荷分别减少了39%~50%和38%~50%,显著提高了水稻生态效益。通过综合效益评估可知,施加5 t生物炭代替化肥是综合效益最高的施肥方法,该施肥方式下氮、磷的年输出负荷分别为16.83、1.89 kg·hm~(-2)。

Influence of combined synthetic fertilizer and biochar applications on nitrogen and phosphorus losses from surface water of paddy field

Fertilization management is an effective measure for controlling non-point source pollution from paddy field. In this paper, nitrogen and phosphorus losses from the surface water of paddy field were investigated during rice growth season under the same inputs of exogenous nitrogen but partial replacement of synthetic fertilizer by different rates of biochar(5 t·hm^-2,10 t·hm^-2 and 20 t·hm^-2). Results showed that TN, NO₃^--N, and NH₄⁺-N concentrations in the surface water of paddy field reached a peak on the third day of fertilization, but decreased rapidly thereafter. TP concentrations showed slow increases 2~4 days after fertilization, but rapidly declined to a stable state after that. Applying biochar had little influence on total phosphorus(TP) in paddy field. Water-soluble phosphorus had the same trend as TP concentration. The critical period to reduce nitrogen and phosphorus loads should be within 10 days after fertilization. Application of biochar mitigated the fluxes of nitrogen and phosphorus outputs from paddy field water by 39%~50% and 38%~50%, respectively. Combined applications of synthetic fertilizer and biochar increased rice production slightly. Based on the recommended application rate of biochar(5 t·hm^-2), the annual nitrogen and phosphorus outputs would be 16.83 kg·hm^-2 and 1.89 kg·hm^-2, respectively.