生物炭对施用沼液稻田土壤重金属生物有效性的影响

Effects of biochar application on the bioavailability of soil heavy metals in paddy fields fertilized with biogas slurry

为探讨施用沼液条件下,添加生物炭对农田土壤重金属生物有效性的影响,以滨海盐土农区稻田为研究对象,设置0、250、500、750 m^(3)∙hm^(-2)四个沼液施用水平(折合施氮量分别为0、205、410、615 kg∙hm^(-2))以及0、15 t∙hm^(-2)两个生物炭用量,对0~20 cm土层土壤重金属(Cu、Zn、Pb、Cd)生物有效性进行研究。结果表明:低沼液用量(250 m^(3)∙hm^(-2))下,无论是否添加生物炭,土壤中四种重金属的弱酸提取态质量分数均无显著变化。中、高沼液用量(500~750 m^(3)∙hm^(-2))下,添加生物炭前,与不施用沼液相比,Cu、Zn、Pb和Cd弱酸提取态质量分数显著提升;添加生物炭后,Cu和Pb弱酸提取态质量分数较添加前显著下降(P<0.05)。添加生物炭前,施用沼液使水稻籽粒中Cu含量增加了44.0%~116.5%,Pb、Cd含量无显著变化。添加生物炭后,中、高沼液用量下籽粒中Zn、Pb和Cd含量无显著变化,但Cu含量降低了21.8%~37.5%(四种重金属含量均低于GB 2762—2017限值)。研究表明,对施用沼液稻田而言,添加生物炭能显著降低土壤中Cu和Pb的生物有效性,是降低水稻籽粒中Cu含量的有效措施。

To determine the influence of biochar on the bioavailability of heavy metals in farmland soil fertilized with biogas slurry,four biogas slurry application levels of 0,250,500 m^(3)∙hm^(-2),and 750 m^(3)∙hm^(−2) equivalent N application amounts of 0,205,410 kg∙hm^(-2),and 615 kg∙hm^(-2),respectively)and two biochar dosages of 0 t∙hm^(-2) and 15 t∙hm^(-2) were applied to investigate the bioavailability of soil heavy metals(Cu,Zn,Pb,and Cd)at 0~20 cm soil layer in a coastal paddy field.The results showed that the mass fractions of the four heavy metals in the weak acid-extracted form in the soil had no significant changes under the low biogas slurry dosage(250 m^(3)∙hm^(-2)),whether biochar was added or not.When the amount of biogas slurry was increased to 500~750 m^(3)∙hm^(-2),the mass fractions of Cu,Zn,Pb,and Cd in the weak acid extraction state increased significantly in the absence of biochar,but the mass fractions of Cu and Pb were significantly lowered when biochar was added(P<0.05).In the absence of biochar,the application of biogas slurry increased the Cu content in rice grains by 44.0%~116.5%but did not significantly change the Pb and Cd contents.In contrast,in the presence of biochar,the contents of Zn,Pb,and Cd were not significantly changed,but the Cu content in grains was reduced by 21.8%~37.5%under the dosages of medium and high biogas slurry(all four heavy metal contents were below the limit values of GB 2762—2017).Our results indicated that addition of biochar can significantly reduce the bioavailability of Cu and Pb in paddy soils under biogas slurry application and that it is an effective measure to reduce the Cu content in rice grains in paddy fields fertilized with biogas slurry.