沼液施用条件下添加浮萍对稻田氮素流失和Cu、Pb变化的影响

养分流失和重金属积累是沼液还田资源化利用过程中的主要问题。为探讨利用浮萍吸收氮磷、富集重金属的能力调控沼液施用中环境污染问题的可行性,在上海市金山区开展了水稻田间试验,研究沼液施用条件下添加浮萍对稻田氮素流失和Cu、Pb的影响。试验设置4个处理:常规化肥、常规化肥+浮萍、沼液全量替代化肥和沼液全量替代化肥+浮萍,测定并比较了不同处理下稻田田面水氮素浓度变化、径流水氮素流失负荷,土壤、水稻籽粒及秸秆中Cu和Pb含量差异。结果表明:不同处理田面水总氮、铵态氮(NH_4~+-N)浓度变化趋势基本一致,均在每次施肥后第1d达到峰值,此后逐日递减,在施肥后第5d降至峰值的30%以下;硝态氮(NO_3~–-N)浓度峰值滞后3～7 d。稻田中添加浮萍能够显著降低田面水TN含量,沼液全量替代化肥+浮萍处理的TN总径流流失负荷为3.67 kg·hm~(-2),比常规化肥处理显著降低37.2%。沼液全量替代化肥+浮萍处理土壤Cu和Pb含量为22.65mg·kg~(-1)和49.05mg·kg~(-1),与其他处理间无显著差异;但土壤有效态Cu和Pb含量较常规化肥处理显著提高18.6%和17.5%。不同处理水稻秸秆Cu和Pb、籽粒Pb含量无显著差异,但沼液全量替代化肥+浮萍处理水稻籽粒Cu含量较沼液全量替代化肥处理显著减少41.1%。综上,沼液施用条件下添加浮萍可以降低稻田氮素流失,在控制土壤、籽粒和秸秆中重金属Cu和Pb含量增加方面具有一定效果,在短期内可以作为沼液还田模式下水体和土壤污染有效的调控手段。

Nitrogen losses and Cu, Pb changes of paddy field affected by adding duckweed under biogas slurry application

Nutrient loss and heavy metal accumulation are major problems in the utilization of biogas slurry as a resource. Duckweed, which can absorb nitrogen and phosphorus and take up heavy metals, can be used to control environmental pollution in biogas slurry irrigation. To study the effects of duckweed on nitrogen loss and reduction in Cu and Pb heavy metals in a paddy field fertilized with biogas slurry, a field experiment was conducted in Jinshan District, Shanghai, China. The experiment comprised four treatments: (1) chemical fertilization (CF); (2) chemical fertilization + duckweed (CF + D); (3) biogas slurry (BS); (4) biogas slurry + duckweed (BS + D). The changes in nitrogen concentration in paddy field surface water, nitrogen-loss load in runoff water, and the levels of Cu and Pb in soil, rice grain and straw under different treatments were measured and compared. The results showed that the trends in the variation of total nitrogen (TN) and ammonia nitrogen (NH₄⁺-N) concentrations in the surface water of different treatments were the same. The concentrations reached peak values on the first day after each fertilization, and then decreased day by day. On the fifth day after fertilization, they dropped below 30% of the peak. The peak value of nitrate nitrogen (NO₃^--N) concentration lagged by 3-7 days. The addition of duckweed when biogas slurry application significantly reduced TN content in surface water, and the total TN loss load of BS+D treatment was 3.67 kg·hm^-2. Compared with the CF treatment, the TN loss load with BS+D treatment was lower by 37.2%. The Cu and Pb contents of the soil treated with BS+D was 22.65 mg·kg^-1 and 49.05 mg·kg^-1, which was not significantly different to levels in the other treatments, but the available Cu and Pb levels in the soil treated with BS+D treatment were significantly higher than those treated with CF, by 18.6% and 17.5%, respectively. There was no significant difference in the contents of Cu and Pb in rice straw and grain, but the grain content of Cu in BS+D treatment decreased by 41.1% compared with BS treatment. In summary, adding duckweed to field applied with biogas slurry can reduce nitrogen loss in paddy fields, and can control the increase of Cu and Pb in soil and rice grain and straw to a certain extent. It can be an effective means to control water and soil pollution under biogas slurry irrigation mode.