New Algorithm of Clay CEC for Soils in Tropical and Subtropical Regions of South China

Clay CEC is one of identification indexes of the LAC-ferric horizon which is the diagnostic horizon of ferrosols in Chinese Soil Taxonomy, and it is defined as soil CEC × 1000/clay content, rather than the measured CEC of the extracted clays;however, such a calculation method would definitely lead to an overestimation of clay CEC because it doesn’t remove the contribution to soil CEC from other soil parameters. In this study, the physiochemical data of the subhorizons from 82 soil series in the tropical and subtropical regions in south China were used, clay CEC was calculated according to the current formula and measured after clays being extracted, the measured and calculated clay CEC were compared, the influencing factors were analyzed for their difference, and the new algorithms were established for clay CEC. The results showed that the measured clay CEC was 21.86% - 99.53% with a mean of 66.88% of the calculated one (significantly lower at p < 0.01), and their difference was significantly correlated with the contents of clays, sand and OM, and mainly decided by the contents of clays and Fe2O3 (the contribution was 52.51% and 25.36%, respectively). By comparison of established regression models of clay CEC with other soil parameters, two new algorithms were recommended for clay CEC as follows: 1) Clay CEC = 10.32 − 0.14pH − 0.05OM − 0.11Fe2O3 + 0.01Silt − 0.01Clay + 1.17CECsoil, R2 = 0.705, P < 0.01;2) Clay CEC = −3.40 + 0.01Sand + 0.02Silt + 1.05CECsoil, R2 = 0.589, P < 0.01).

川西名山县阶地漂洗土壤分类及参比研究

经历了强烈漂洗作用的土壤是一类形态独特的土壤,在分类系统中具有重要地位。本文在四川西部漂洗土壤集中分布的名山县第二至五级阶地上对这类土壤进行了野外调查采样和室内测试分析,按中国土壤系统分类的原理和方法,通过水耕表层、水耕氧化还原层、漂白层、人为滞水土壤水分状况、氧化还原特征等诊断层和诊断特性的确定及按顺序检索的方法,将其归入人为土纲,水耕人为土亚纲,简育水耕人为土和铁聚水耕人为土土类,漂白简育水耕人为土、漂白铁聚水耕人为土和普通铁聚水耕人为土亚类;同时按发生分类系统进行了类型划分,它们均归入漂洗水稻土亚类。比较而言,系统分类能更精确地区别土壤分异,有利于土壤精准化管理,但仍需进一步修订完善。

长江三角洲水稻土主要土种在中国土壤系统分类中的归属

本文概述了长江三角洲水稻土的形成背景,说明了我国水稻土与水耕人为土分类上的区别。在此基础上,将长江三角洲水稻土主要土种按中国土壤系统分类的严格定量指标,分别阐明其在系统分类中的归属。