耕作方式对稻-油轮作系统土壤理化性质及重金属有效性的影响

为探明不同耕作方式下稻-油轮作系统中土壤重金属有效性的变化规律,测定了21年长期定位试验稻-油轮作系统中土壤及其剖面的主要理化性质和重金属有效含量,分析了二者间的关系。结果表明,与翻耕相比,垄作免耕使各土层土壤有机质含量和阳离子交换量显著提高,并具有明显的表层聚集现象,土壤pH值明显降低。耕层土壤Cd、Cu和Zn有效量以垄作免耕处理最高,土壤Pb的有效量则以常规平作处理最高,不同耕作方式下,土壤有效Cd和Pb出现表聚现象,但有效Zn和Cu随土壤深度的变化无明显规律。相关分析表明,土壤有机质含量与土壤Cd、Zn有效量呈极显著正相关关系,与土壤Pb、Cu有效量呈显著正相关,土壤pH值与土壤Pb有效量呈显著正相关,而土壤阳离子交换量与4种重金属有效量间的相关性不显著。由此推测,耕作方式主要是通过影响土壤有机质含量而影响重金属元素的有效性,垄作免耕较翻耕在改良土壤理化性质上有较大优势,却使0-20cm和20-40cm土层重金属有效量显著增加,表现出明显的表层富集趋势。

Effects of Tillage Methods on Physicochemical Properties and Heavy Metal Availability of Soils in Rice-rape Rotation Systems

To explore the effects of tillage methods on soil physicochemical properties and heavy metal availability of soils in rice-rape rotation systems,a long term field experiment,which consists of five treatments and has lasted for 21 years,was conducted.The results showed that compared with the conventional tillage,the contents of organic matter and cation exchange capacity in the ridge and no-tillage treatment with surface upper-accumulated pattern,increased significantly,but the pH decreased significantly.The availability of Cd,Cu,and Zn in soils was highest in the ridge and no-tillage treatment,while the availability of Pb was highest in the conventional tillage treatment.The availability of Cd and Pb decreased with increase of soil depth,but there was no obvious trend for the availability of Cu and Zn in soil.The correlation analysis showed that the organic matter content was best correlated with the availability of Cd and Zn,and was also significantly correlated to the availability of Cu and Pb in soil.There was no significant correlation between cation exchange capacity and the availability of heavy metal.The results obtained in present study implied that the effects of tillage method on the availability of soil heavy metal was caused by the changes of organic matter contents.Compared with the conventional tillage,the ridge and no-tillage had more advantages in improving the physicochemical characters of soils,but increased the availability of Cu,Zn,and Pb in the depth of 0-40 cm.