Juliana Prevedello

Soil hydro-physical changes in natural grassland of southern Brazil subjected to burning management

Burning of vegetation can promote changes in soil physical properties and also create hydrophobic substances, which accumulate and result in the formation of water-repellent layers. A study was conducted between 2005 and 2011 on an Albaqualf, with natural grassland composed mainly of Andropogon lateralis, in southern Brazil, to investigate the induction of hydrophobicity by burning and changes in the soil hydro-physical characteristics. The treatments consisted of no burning, and burned 60, 36, 12, 6, 4, and 2 months before sampling. Burning management did not change the saturated hydraulic conductivity, whereas air permeability was significantly reduced in the surface layer, nearly reaching the original values 4 months after burning. Saturated hydraulic conductivity and air permeability correlated with total porosity and macroporosity. The surface layer was the most sensitive to fire effects, with an increased degree of hydrophobicity for up to 2 months after vegetation burning. Hydrophobicity and contact angle correlated positively with soil organic matter content.

MANEJO DO SOLO E CRESCIMENTO INICIAL DE Eucalyptus grandis Hill ex Maiden EM ARGISSOLO

The forest species cultivation with rapid growth in Brazil has increased, mainly due to the diverse use of its wood and climate adaptation. The cultivation with minimum tillage in the forest sector stands out a way to increase productivity, combined with the maintenance of biodiversity and soil conservation. This study was conducted at the experimental area of State Foundation for Agricultural Research - Research Center for Forestry in Santa Maria - RS, with aimed to evaluate the effect of the soil tillage methods on soil physical properties and on initial development of Eucalyptus grandis, in a sandy loam Typic Hapludalf. Four soil management practices were compared: no-tillage; chisel tillage; chisel tillage plus harrowing and; rotary tillage (rotary tiller), installed in a randomized block design with three replications. The soil under no-tillage conditioned lower initial growth of eucalyptus due higher soil penetration resistance and bulk density, when compared with treatments with mobilization. The root distribution analysis in soil, despite being a qualitative method, was effective in demonstrating the effect of soil tillage for the Eucalyptus grandis

ORIGEM DOS COMPOSTOS HIDROFÓBICOS E SEUS EFEITOS EM FLORESTAS DE Pinus E Eucalyptus

A hidrofobicidade pode ser entendida como a repelencia do solo a agua, dificultando o seu molhamento. Esse fenomeno esta associado ao recobrimento das particulas do solo por substâncias orgânicas hidrofobicas, sendo que atualmente existem inumeros relatos de repelencia a agua em areas de florestas de Eucalyptus e Pinus. Assim, este trabalho teve por objetivo revisar e elencar os aspectos relacionados a origem dos compostos hidrofobicos e os seus efeitos na dinâmica da agua no ambiente florestal, alem de implicacoes no crescimento e desenvolvimento das arvores em florestas de Eucalyptus e Pinus. Reconhece-se que a vegetacao local e algumas bacterias e fungos, em funcao da sua composicao quimica, podem liberar substâncias orgânicas hidrofobas. Outro fator condicionante e a ocorrencia de incendios e queimadas, que induzem alteracoes nos compostos orgânicos e promovem o secamento do solo. Alem disso, a composicao granulometrica e o pH do solo podem estar indiretamente associados a ocorrencia de repelencia a agua no solo. A existencia de hidrofobicidade exige uma atencao diferenciada, principalmente em relacao ao uso e manejo do solo, pois afeta diretamente o movimento da agua na superficie e no interior do perfil de solo. Alteracoes na sortividade, reducao da taxa de infiltracao, escoamento superficial elevado e ocorrencia de fluxo preferencial sao os principais efeitos hidrologicos desse fenomeno. Em funcao das menores taxas de infiltracao ha aumento do escoamento superficial e reducao da quantidade de agua disponivel, potencializando o processo erosivo e, consequentemente, afetando o crescimento e o desenvolvimento das plantas.