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Eucalyptus tree stocking can be adjusted to increase, depending on purpose, cellulose, timber or bioenergy production, but the effect of stocking on ecosystem water balance is still understudied. Studies on soil and catchment hydrology and forest management, encompassing distinct climatic years, are needed for understudied ecosystems to improve water use efficiency and streamflow regulation, and thus bridging forestry and ecosystem processes. For different Eucalyptus dunnii stockings, we measured rainfall dynamics to quantify rainfall partitioning, soil water balance, and eucalyptus water use efficiency in a sandy soil. Total rainfall, throughfall, stemflow, canopy interception, evapotranspiration, tree growth, and water use efficiency were evaluated over a 1-year study period (5th to 6th years after planting), in low (LS: 816 trees ha−1), medium (M: 1,633 trees ha−1), medium–high (MH: 3,265 trees ha−1), and high tree stockings (HS: 6,568 trees ha−1). Tree stocking had no clear relation with the partitioning of annual rainfall (P, 2583 mm) into canopy interception (34–37% of P) and effective rainfall (63–66% of P). By increasing tree stocking from 816 to 6,568 trees ha−1, throughfall decreased from 62 to 53% of P, and stemflow increased from 2.1 to 12.7% of P. Estimated deep drainage was

Water repellency is associated to coating of soil particles by hydrophobic substances, usually of organic origin, affecting water dynamics in soil matrix. We analyzed the effect of water repellency on water sorptivity of topsoil aggregates of six soil types under three initial moisture conditions (10 kPa, 100 kPa, and air-dried). Undisturbed soil samples were collected to evaluate sorptivity in the 0–5 cm soil layer at different locations in Pampa Biome in southern Brazil. Disturbed soil samples were also collected for soil particle size distribution, particle density and organic matter content. Sorptivity test was conducted in a tension micro-infiltrometer, using distilled water and ethanol (95% v/v). High values of repellency index R (13.43 in Hapludert, and 8.98 in Dystrudept) of soil aggregates reduced sorptivity and restricted infiltration properties. Repellency index decreased sharply with increase in soil moisture. Therefore, for hydrophobic soils an increase in soil moisture of original air-dry soil reduces hydrophobicity and enhances sorptivity and water infiltration into soil aggregates. High values of water repellency modifies water dynamics in soil aggregates, concealing the effects of matric potential and generating different patterns of conventional water infiltration behavior, especially in dry soil conditions.

The soil hydrophobicity can be understood as soil water repellency or difficulty in wetness. This phenomenon is associated with the covering soil particles and hydrophobic organic compounds reducing the soil sorptivity and hence infiltration of water. The objectives of this study were to determine the level of hydrophobicity in the soil and assess its relationship with resistance and size distribution of water stable aggregates, particle size distribution and organic matter content of different soils in southern Brazil. Undisturbed soil samples were collected in different soil layers, 0–5, 5–10 and 10–20 cm, to determine soil sorptivity, geometric mean diameter and aggregate stability index while granulometric composition and organic matter content were determined using disturbed soil samples. The sorptivity test was conducted using a tension micro-infiltrometer, with two different liquids, distilled water and ethanol (95% v/v). The proportions of sand, silt and clay did not correlate significantly with the occurrence of hydrophobicity. In the hydrophobic soils, hydrophobicity index is directly associated with high organic matter contents and did not correlate with the particle size distribution. For the hydrophobic aggregates, cohesive forces between the particles acted for long period as a result of slow wetting, which led to an increase in geometric mean diameter, stability index of water stable aggregates and consequently greater resistance to the disintegrating actions of associated agents.

article Hydrophobicity is a soil water repellency phenomenon, which results in difficulty of soil wetting. The objectives of this study were to determine the hydrophobicity index and water-soil contact angle for different soil classes and to define the threshold water content beyond which hydrophobic soils become hydrophilic. Soil samples were collected from nine soils in southern Brazil, where vegetation was composed mainly of natural grassland species. Undisturbed soil samples were collected in three soil layers (0-5, 5-10 and 10-20 cm) for the determi- nation of bulk density, total porosity, macroporosity, microporosity and water retention curve. In these same layers, additional samples were collected for the evaluation of repellency index and soil-water contact angle; while soil sorptivity was analyzed using a micro tension infiltrometer. Among the soils, Hapludert, Dystrudept, Haplaquents and Albaqualf showed high hydrophobicity index and soil-water contact angles in the air-dried medium at three sampled soil layers, ranging from 0 to 20 cm depth. In hydrophobic soils, the repellency index and hydrophobicity persistence in the soil decreased with depth, reduction in organic content, and in- crease in water content. The Haplaquents and Endoaqualfs had greatest repellency index until the volumetric water content equilibrated reached tension of 10 kPa. The threshold water content beyond which hydrophobic soils becomehydrophilic(θh )v ariedfrom0.36to0.57 cm

A agregação pode sofrer alterações permanentes ou temporárias com variações cíclicas provocadas por práticas de manejo do solo e pelo crescimento das plantas. O estudo avaliou a variação temporal e espacial da estabilidade de agregados estáveis em água e a sua relação com o conteúdo de matéria orgânica em um Argissolo em Santa Maria, RS, Brasil. Os tratamentos avaliados foram quatro sistemas de preparo do solo para implantação de povoamento de Eucalyptus grandis: plantio direto; escarificação; escarificação seguida de gradagem e enxada rotativa. Amostras de solo foram coletadas na camada de 0,00-0,05 m para a determinação da densidade, da estabilidade dos agregados estáveis em água e do teor de matéria orgânica do solo. A escarificação, escarificação seguida de gradagem e enxada rotativa resultaram em menor estabilidade estrutural de agregados estáveis em água. Os efeitos negativos do preparo do solo sobre o Argissolo de textura franco arenosa são reduzidos após 12 meses, demonstrando sua capacidade em reestabelecer a estrutura e a agregação. Os diferentes preparos do solo avaliados não foram capazes de aumentar o teor de carbono orgânico, não influenciado no estado de agregação. O crescimento inicial do eucalipto foi favorecido com a intensificação do preparo do solo. Aggregation can suffer permanent or temporary changes to cyclical variations induced by management practices for soil and plant growth. The study evaluated the temporal and spatial variation of the stability of water stable aggregates and its relationship with the organic matter content in an Hapludalf in Santa Maria municipality, Rio Grande do Sul State, Brazil. The treatments were four tillage systems for deployment of Eucalyptus grandis : no-tillage, chisel, chisel tillage plus harrowing and rotary tiller. Soil samples were collected in the layer of 0.00 to 0.05 m for determination of the density, and stability in water of stable organic matter aggregates contents of the soil. Chisel, chisel tillage plus harrowing and rotary tiller resulted in lower structural stability of water stable aggregates. The negative effects of tillage on Hapludalf with sandy loam texture are reduced after 12 months, demonstrating its ability to restore the structure and aggregation. The soil tillage evaluated did not increase the carbon content and that was not influenced by the state of aggregation. The early growth of Eucalyptus was favored by the intensification of soil tillage.

Hydrophobicity is the phenomenon where the soil has reduced wettability, usually associated with coating of soil particles by hydrophobic organic substances. This study aimed to provide a description of the hydrophobicity occurrence, highlight recent discoveries about the origin of phenomenon and discuss the main hydro-physical properties and chemical processes linked to the development of hydrophobic behavior in soils. Hydrophobicity is associated with other factors such as soil moisture, presence of some fungi species, particle size, soil pH and occurrence of burnings. The causative substances may be provided by local vegetation, through deposition or decomposition. The dependence and combination of different factors that influence hydrophobicity in soils lead to a spatial and temporal variability of the phenomenon, with negative consequences in the processes of infiltration and water percolation, affecting the three-dimensional distribution and dynamics of soil moisture. Thus, the occurrence of a hydrophobic character requires special attention, especially regarding soil use and management. A hidrofobicidade é o fenômeno em que o solo apresenta dificuldade de se umedecer com a água, normalmente associado ao recobrimento das partículas do solo por substâncias orgânicas hidrofóbicas. Assim, este trabalho tem como objetivo fazer uma descrição da ocorrência da hidrofobicidade, ressaltando as recentes descobertas em relação à origem do fenômeno, enfocando as principais propriedades físico-hídricas e processos físico-químicos ligados ao desenvolvimento do caráter hidrofóbico no solo. As substâncias orgânicas responsáveis pela repelência podem recobrir total ou parcialmente as partículas, agregados e paredes dos poros, transmitindo diferentes graus de hidrofobicidade ao solo. Essas substâncias podem ser oriundas da vegetação local, via deposição ou decomposição, porém a hidrofobicidade pode estar associada a outros fatores como a umidade do solo, a presença de algumas espécies de fungos, a composição granulométrica, o pH do solo e a ocorrência de queimadas. A dependência e a combinação dos diferentes fatores que influenciam na ocorrência de hidrofobicidade nos solos levam a uma variabilidade espacial e temporal do fenômeno, com consequências negativas nos processos de infiltração e percolação da água, afetando a distribuição tridimensional e dinâmica da umidade do solo. Dessa forma, a ocorrência do caráter hidrofóbico exige uma atenção diferenciada, principalmente em relação ao uso e manejo do solo.