Resumo

HOSSNE G., Américo J.. Bulk Density and its Agricultural Implications in the Soil Expansion/Shrinkage Process. Terra Latinoam [online]. 2008, vol.26, n.3, pp.195-202. ISSN 2395-8030.

In the process of soil expansion/shrinkage caused by changes in water content, total volume of a given mass of soil varies due to the variations in void volume, producing changes in bulk density. The sandy loam kaolinitic soil of the Venezuelan savanna exhibits tenacity and fragmentation when moisture content is low. The objectives of this study were (a) to present new algebraic expressions for the indexation of agricultural soil involving water content, dry (ρ_S = M_S/V_T) or natural (ρ_N = M_T/V_T) density, soil void volume, and solidity relationship (i_S = V_S/V_T), (b) to use an experimental procedure to analyze the behavior of the functions ρ_S = f (w, V_V), ρ_N = f (w, V_V) and the differential variations of dρ_S / dV_V, and dρ_N / dV_V , and (c) to study the relationships, implications, and uses in agriculture. An algebraic procedure was used with known indexes to define the introduced mathematical expressions, the method of linear contraction to find the relationship between densities, water content and void volume, and regression analysis to study the variations among the parameters. Results and conclusions obtained were (a) new relationships for the dry and natural bulk densities according to i_S, w, and θ_W, (b) bulk densities vary linearly and are inversely proportional with respect to w and V_V correlate more highly with V_V, (c) the differential variations are inversely proportional to V_V with strong linear correlation, (d) natural bulk density should be used to evaluate the expansion/contraction state and compaction of agricultural soils, and (e) soil water content and void volume should be provided together with density data.

Palavras-chave : soil linear contraction; savanna Ultisol; kaolinitic soil; porous volume; differential variability of dρ_s /dV_V.