Influência da concentração de extratos hidrofóbicos na repelência à água em solos arenosos

Abstract

Resumo -A repelência à água é estudada em vários solos do mundo, sendo os casos mais extremos encontrados em solos arenosos. Acredita-se que a repelência à água seja causada pelo recobrimento das partículas do solo por compostos hidrofóbicos derivados da decomposição de plantas. Este trabalho avaliou a influência da concentração de extratos hidrofóbicos de um Neossolo sob plantio de Pinus taeda, na repelência à água em amostras de um solo arenoso preparado em laboratório, com diferentes teores de matéria orgânica. Os extratos hidrofóbicos do solo original foram extraídos com clorofórmio:acetona, seguido de isopropanol:amônia. Os tratamentos constaram de mistura de areia com sete níveis de matéria orgânica (0%; 3%; 6,5%; 6,5% + 10% de ácido húmico (AH); 6,5% + 30% de AH; 6,5% + 50% de AH; e 10%), aos quais foram aplicadas três concentrações de extrato hidrofóbico (CEH). As amostras foram secas a diversas temperaturas antes dos testes de repelência. As CEHs induziram à repelência à água nos tratamentos, em diferentes intensidades, porém estes valores foram inferiores aos encontrados no solo original. Os tratamentos com CEH de 2,88 g kg -1 tiveram os maiores tempos de repelência. Termos de indexação: Hidrofobicidade, Pinus taeda, WDPT. Water repellency of sandy soil as a function of hydrophobic concentrationAbstract -Soil water repellency has been reported worldwide being most extremes cases observed in sandy soils. Soil water repellency is accepted to be caused by recovering of soil particles by hydrophobic compounds originated from plant decomposition. This work aimed to evaluate the influence of concentration of hydrophobic extracts from a forest soil under Pinus taeda on water repellency of sandy soil with different organic matter content. Hydrophobic compounds were extracted from a severely hydrophobic Lithosol, using chloroform:acetone, followed by isopropanol:ammonia. The water drops penetration time test (WDPT) was applied in dried samples under four temperatures, seven treatments (sand with 0%; 3%; 6.5%; 6.5% + 10% of humic acid (AH); 6,5% + 30% of AH; 6.5% + 50% of AH; and 10% of charcoal as organic matter), and three levels of hydrophobic extract. The extracted material induced hydrophobicity in all treatments, in variable intensity, but lower than those found in the original Lithosol. Treatments with extract level 1 (2.88 g kg -1 ) presented the highest times of water repellency.

Hydro-physical processes and soil properties correlated with origin of soil hydrophobicity

“…The second group is formed by amphiphilic substances of polar structure, with a hydrocarbon chain (hydrophobic) with terminal functional group of positive or negative charge with hydrophilic character (KLEBER & JOHNSON, 2010). Organic molecules consisting of long chain fatty acids are the major hydrophobic substances found in soils (CAMBRONERO et al, 2011). However, more research is needed to accurately characterize the chemically compounds that cause water repellency (BAYER & SCHAUMANN et al, 2007).…”

“…Hydrophobic soils restrict the entry of water, which 'balls up' or sits on the soil in beads rather than infi ltrating the soil (CAMBRONERO et al, 2011). The repellency comes from a mutual attraction between water and solid surfaces (adhesion) or between water molecules (cohesion).…”

“…The fi rst consists of long chain hydrocarbons and aliphatic structure (CAMBRONERO et al, 2011). These compounds are polar, that is, they have no negative or positive charge at the end of the chain and are almost insoluble in water, showing hydrophobic character .…”

“…Occurrence and variability of hydrophobicity in the soil Hydrophobicity has been documented in various locations and soil and climatic conditions, found in humid tropical climates (VOGELMANN et al, 2010;CAMBRONERO et al, 2011), in humid and cold climates of northern Europe (DLAPA et al, 2008, WAHL, 2008, or even in regions of warm and dry climate of central Australia (THWAITES et al, 2006) or in Mediterranean climate of southwest Europe (MATAIX-SOLERA et al, 2007;RODRÍGUEZ-ALLERES et al, 2007;KEIZER et al, 2007). In the literature, there are vast records of this phenomenon in a wide variety of soils, from sandy to clay soils, the highly to low weathered, very acidic to alkaline and fertile to less fertile (MÜLLER & DEURER, 2011).…”