ORGANIC CARBON AND TOTAL NITROGEN IN THE DENSIMETRIC FRACTIONS OF ORGANIC MATTER UNDER DIFFERENT SOIL MANAGEMENT

ABSTRACT: The evaluation of land use and management by the measurement of soil organic matter and its fractions has gained attention since it helps in the understanding of the dynamics of their contribution to soil productivity, especially in tropical environments. This study was conducted in the municipality of Colorado do Oeste, state of Rondônia, Brazil and its aim was to determinethe quantity of organic carbon and total nitrogen in the light and heavy fractions of organic matter in the surface layers of a typic hapludalf under different land use systems: Native Forest: open evergreen forest, reference environment; Agroforestry System 1: teak (Tectona grandis LF) and kudzu (Pueraria montana); Agroforestry System 2: coffee (Coffea canephora), marandu palisade grass (Brachiaria brizantha cv. Marandu), "pinho cuiabano" (Parkia multijuga), teak and kudzu.; Agroforestry System 3: teak and cocoa (Theobroma cacao); Silvopasture System: teak, cocoa and marandu palisade grass; and Extensive Grazing System: marandu palisade grass. The experimental design was a randomized block in split-split plots (use systems versus soil layers of 0-0.05 and 0.05-0.10 m) with three replications. The results showed that relative to Native Forest, the Agroforestry System 2 had equal- and greater amounts of organic carbon and total nitrogen respectively (light and heavy fractions) in the soil organic matter, with the light fraction being responsible for storage of approximately 45% and 70% of the organic carbon and total nitrogen, respectively. Therefore, the light densimetric fraction proved to be useful in the early identification of the general decline of the soil organic matter in the land use systems evaluated.

摘要：通过测定土壤有机质及其组分来评估土地利用与管理方式的研究日益受到关注，因其有助于解析其对土壤生产力的贡献动态，在热带环境中尤为关键。本研究于巴西朗多尼亚州（Rondônia）西部科罗拉多市（Colorado do Oeste）开展，旨在明确典型强发育湿润淋溶土（Typic Hapludalf）表层土壤中，不同土地利用系统下有机质轻组与重组组分的有机碳及全氮含量。供试土地利用系统包括：原生林（开放常绿林，作为参照环境）；农林复合系统1：柚木（Tectona grandis LF）与野葛（Pueraria montana）；农林复合系统2：刚果咖啡（Coffea canephora）、马兰多栅栏草（Brachiaria brizantha cv. Marandu）、‘pinho cuiabano’（Parkia multijuga）、柚木与野葛；农林复合系统3：柚木与可可（Theobroma cacao）；林牧复合系统：柚木、可可与马兰多栅栏草；以及粗放放牧系统：仅种植马兰多栅栏草。本试验采用裂裂区随机区组设计，以土地利用系统为主区，0~0.05 m和0.05~0.10 m土层为副区，设置3次重复。结果表明，相较于原生林，农林复合系统2的土壤有机质轻组与重组中有机碳和全氮含量分别与之持平或更高；其中轻组组分分别储存了约45%的有机碳与70%的全氮。综上，轻组密度分级法可用于早期识别所评估的各土地利用系统中土壤有机质的整体衰退趋势。