淹水条件下控释氮肥对污染红壤中重金属有效性的影响

采用淹水培养方法研究了不同氮水平(100、200和400 mg/kg,分别记为1、2、3)下普通尿素(PU)、硫包膜尿素(SCU)、树脂包膜尿素(PCU)和硫加树脂双层包膜尿素(SPCU)对污染红壤中Cd、Pb、Cu、Zn有效性的影响.结果表明,不同包膜尿素对土壤pH值和水溶性SO42-含量有较大影响.各施氮处理红壤pH值随着施氮量的增加(除5d时PU和60 d时SCU)而增加,不同包膜尿素对土壤中水溶性SO42-含量有较大影响,在同一施氮水平下不同包膜尿素处理间土壤pH值和土壤中水溶性SO42-含量差异较大.60 d培养期间PU、SCU、PCU和SPCU处理pH值比对照分别升高0.17-0.38、0.08-0.27、0.07-0.36和0.10-0.21;水溶性SO42-含量PU、SCU和PCU处理比对照分别升高39.5％-157.3％、40.9％-94.5％和7.55％-55.8％,而SPCU处理降低5.67％-90.7％.不同尿素类型和氮肥的施用量对红壤Cd、Pb、Cu和Zn有效性的影响均存在显著差异.60 d培养期间红壤有效态Cd含量以树脂包膜尿素100 mg N/kg下最低,其有效态Cd含量比对照显著降低20.7％-69.8％；有效态Pb、Cu和Zn含量以普通尿素400 mg N/kg下最低,其有效态Pb、Cu和Zn含量比对照分别显著降低17.0％-54.2％、18.5％-34.6％和15.6％-59.5％.随施氮量提高,PU处理有效态Cd含量先升高后降低,有效态Pb、Cu和Zn含量逐渐降低；SCU处理有效态Pb含量逐渐降低,有效态Cd、Cu和Zn含量变化规律不一致；PCU处理有效态Cd含量逐渐升高,有效态Pb、Cu和Zn含量变化规律不一致；SPCU处理有效态Cd、Pb、Cu和Zn含量逐渐降低.有效态Pb和Zn含量与pH值和水溶性SO42-含量呈显著负相关,有效态Cd与水溶性SO42-含量呈显著正相关.在多重金属污染红壤中,可考虑不同控释氮肥的配合使用,降低土壤中重金属的有效性.

Effect of different controlled-release nitrogen fertilizers on availability of heavy metals in contaminated red soils under waterlogged conditions

The effects of prilled urea (PU), sulfur coated urea (SCU), polymer coated urea (PCU), and sulphur-polymer-terresin coated urea (SPCU) were studied on the availability of Cd, Pb, Cu, Zn in contaminated red paddy soils under different nitrogen levels (100, 200 and 400 mg/kg, respectively noted as 1, 2, 3) using the waterlogged incubation method. The results showed that application of different coated release-controlled urea could significantly affect the pH value and the contents of water-soluble SO₄^2- in the soil. The pH values of red soil of each application nitrogen treatment increased with increasing nitrogen level (except PU treatment on 5th day and SCU treatment on 60th day). The application of different coated release-controlled urea could significantly affect the contents of water-soluble SO₄^2- in the soil. The pH value and contents of water-soluble SO₄^2- were significantly different among different coated release-controlled urea under the same nitrogen level. The pH values of soil of the treatments PU, SCU, PCU and SPCU increased by 0.17-0.38, 0.08-0.27, 0.07-0.36, and 0.10-0.21, respectively in the whole 60 days incubation duration compared to the control. The contents of water-soluble SO₄^2- in soil of the treatments PU, SCU and PCU increased by 39.5%-157.3%, 40.9%-94.5%, and 7.55%-55.8%, respectively whereas, decreased by 5.67%-90.7% in soil of the treatment SPCU. There were significant differences between different coated release-controlled urea types on the availability of Cd, Pb, Cu and Zn. The availability of Cd, Pb, Cu and Zn also varied sharply with the application rates of nitrogen fertilizer. Available Cd content in soil of treatment PCU at 100 mg/kg nitrogen level significantly decreased by 20.7%-69.8% and was the lowest during the whole 60 days incubation. Available Cd content in soil of treatment PU at 200 mg/kg nitrogen level was the highest and significantly increased by 163.5%-181.7% during the whole incubation. Available Pb, Cu and Zn content in soil of treatment PU at 400 mg/kg nitrogen level was the lowest and significantly decreased by 17.0%-54.2%, 18.5%-34.6%, and 15.6%-59.5%, respectively. With increasing the application rates of nitrogen fertilizer, available Cd content in soil of treatment PU increased first and then decreased, while available Pb, Cu and Zn content decreased gradually. With increasing the application rates of nitrogen fertilizer, available Pb content in soil of treatment SCU decreased gradually, while there were not the same regularity of available Cd, Cu and Zn content among the three application nitrogen levels. With increasing the application rates of nitrogen fertilizer, available Cd content in soil of treatment PCU increased gradually, while there were not the same regularity of available Cd, Cu and Zn content among the three application nitrogen levels. With increasing the application rates of nitrogen fertilizer, available Cd, Pb, Cu and Zn content in soil of treatment SPCU decreased gradually. Soil available Pb and Zn were significantly negatively correlated with soil pH and water-soluble SO₄^2- content. Soil available Cd was significantly positively correlated with water-soluble SO₄^2- content. And the soil pH also plays a major role on the behavioral changes of Pb and Zn in the soil. In red paddy soil contaminated by multi-heavy metal, coupling use of different coated urea can effectively control the availability of heavy metals.