Dados do Trabalho

Título

IN SITU FIELD CAPACITY CALCULATION IN BRAZILIAN SOILS

Resumo

Field Capacity (FC) is a key property in Soil Science, but quite unfortunately its meaning and determination method are dubious. Our objective was to formulate a method of in situ FC determination based on the two days of drainage and apply it to a large number of Brazilian soils. Standardized in situ FC determinations were made for 29 profiles (207 samples), and a pedotransfer function (PTF) was obtained relating in situ FC to θ60 (moisture at the 60-cm suction). With the above PTF, it was possible to calculate FC based only on the five van Genuchten parameters. We also obtained the hFC value, the suction at FC. The methodology was applied to 847 samples from HYBRAS (HYdrophysical database for BRAzilian Soils), allowing determining the FC and hFC distributions in HYBRAS’ soil sub-groups. These sub-groups are formed by combinations of three textural groups (coarse, medium and fine-textured soil classes; CT, MT and FT, respectively) with three pedological groups (all soils, weathered and unweathred soils). The weathered group is composed by the intensely weathered tropical soils. The unweathered group corresponds to the other soils. The FC and hFC medians decreased signicantly from the FT to the CT group, with the unweathered medians being larger than the corresponding weathered medians, confirming that texture and pedology play an important role on FC. The coefficients of variation for hFC were large among the sub-groups, which indicates that FC should not be indirectly determined as the water content corresponding to a single and pre-determined suction value. Calculating the drainable porosity, DP (porosity minus FC), only considering the clay textural class within the weathered FT sub-group, its mean was 0.20 m³/m³, a typical DP value for sandy materials, indicating the relevance of the clay nature of weathered profiles on determining soil drainage. So, the proposed methodology can contribute to the understanding and large application of the FC concept.

Palavras-chave

field capacity suction, weathered soils, pedotransfer function

Instituição financiadora

FEDERAL UNIVERSITY OF RIO DE JANEIRO, GEOLOGICAL SURVEY OF BRAZIL