Horizontes com caráter coeso e sua distribuição espacial em solos na Formação Barreiras

Abstract

Soils that present the cohesive character are dense, resistant to knife or pedologic hammer,very to extremely hard when dry and friable or firm when moisted. The genesis of cohesion is not completely understood. The present research was developed to analyze the knowledge already done about cohesive horizons, as well as about innovative tools of evaluating this topic. The actions area divided into three chapters. In the Chapter I, was done a bibliographic revision about soils with cohesive character as well as about strategies to evaluate the spatial distribution of this character. General Characteristics of soils with cohesive horizon were took taking in count the Barreiras Formation area, grouping profiles from the soil surveys done in 70’s and 80’s and considered some variables. The Chapter II aimed to analyze four soil profiles in a topossequence in area with occurrence of cohesive horizon originating from Barreiras Formation sediments and aimed also to analyze the variables through geostatistics searching for variables that contribute to cohesive horizon. The study area is located in the experimental area from EMBRAPA Agroindústria Tropical in Pacajus, CE. We analyzed morphological, chemical and physical aspects. It was identified contribution of relief in the process of soil formation, and the profiles P1 and P2, from the top part, classified as Argissolos Amarelos, the profile P3, with cohesive horizon, classified as Argissolo Acinzentado and the profile P4, in the lowest part, as Neossolo Flúvico. The profile P3 was located in a flat area, with evidences of difficulty drainage and accumulation of fine sand and clay, suggesting the argiluviation as influencing the process of genesis of cohesive horizons. The area showed relief mainly flat, with small variations of slope and curvature. Most of the variables presented spatial dependence and adjusted to spherical model. It was not identified spatial dependence to the variable consistence. The variables gravel, very coarse sand and very fine sand showed higher values in this area. It was identified the relation of cohesive horizons occurrence in flat and concave areas, with low drainage and related to argilluviation processes and fine particles of sand. The geostatistical data did not present relation to argilluviation, but was possible to identify an area of occurrence of cohesive horizon soils.