Silvia Imhoff

Intervalo hídrico ótimo na avaliação de sistemas de pastejo contínuo e rotacionado

Soil physical quality in continuous and short-duration rotational cattle grazing systems was evaluated using the Least Limiting Water Range (LLWR) approach. Soil samples were collected on an experimental site at the Embrapa - Beef Cattle Research Center (Campo Grande, MS, Brazil). The studied soil was a Typic Acrudox. Four sampling sites were selected: two under a short-duration continuous grazing system and two under intensive short-duration rotational grazing system. Thirty soil cores were collected in each site under the continuous grazing system, planted with Brachiaria decumbens cv. Basilisk grass. One of the continuous grazing sites had received biannual fertilization (Cc) while the other had not been fertilized (Cs). Thirty soil cores were also collected in each site under the intensive rotational grazing system, planted with Panicum maximum cv. Tanzania grass. In the intensive rotational grazing system the two sites differed in relation to the post-graze residue level left. In one site (R1) it varied from 2.0 to 2.5 t total dry matter (TDM) ha-1 and in the other R2 it varied from 3.0 to 3.5 t TDM ha-1. The cores were subjected to a soil water suction gradient, and then used for soil bulk density (Db), soil resistance to penetration (SR), volumetric water content (qv), and LLWR determinations. The intensive short-duration rotational grazing system presented the worse physical soil conditions for plant growth, as evaluated by the LLWR. The highest Db and the lowest LLWR were found in R1, which could be a consequence of the heavier stocking rates used on this site.

Quantification of the soil physical quality of a tropical oxisol using the S index

Soil physical quality is fundamental for the sustainability of agro ecosystems. Soil physical quality assessment must be developed using parameters that describe physical behavior. S, a new soil physical parameter has recently been introduced for assessing the soil physical quality. A good soil physical quality has been associated with values of S > 0.035 in soils from temperate climates. However, S has not been evaluated in tropical soils yet. Therefore we tested the hypothesis that S is a reliable soil physical quality indicator of a Typic Hapludox cropped with maize under no-tillage (NT) and conventional tillage (CT). Undisturbed samples were collected from each tillage system in the row and interrow positions. Soil bulk density was determined in the samples and the S parameter was calculated using a pedotransfer function from the same samples. The parameter S was able to differentiate tillage and position with SNT < SCT independent of the row and interrow sampling positions. Higher S values were verified in row position than in the interrow in both tillage systems. With the use of a pedotransfer function it was also possible to establish a negative relationship between S and soil compaction. The results confirmed our hypothesis and suggest that further studies should be carried out to evaluate S in other tropical soils and management systems.

Plant response to mechanical resistance and air-filled porosity of soils under conventional and no-tillage system

Roots may respond to restrictive soil physical conditions and send signals to shoots to control plant growth. Soil mechanical resistance and aeration can be managed to improve the soil physical conditions for plant growth by using different tillage systems. The objective of this study was to quantify the influence of no-tillage and conventional-tillage systems on plant response to soil mechanical resistance and aeration. The study was carried out on a farm, cultivated with corn, with a side-by-side comparison of no-tillage and conventional-tillage systems. Thirty-two paired sampling sites were located along two transects, located one in each treatment. Soil water content, bulk density, and plant growth were measured in each treatment. Based on the soil water and bulk density measurements, the air-filled porosity values were computed for each treatment. Soil water contents and bulk density values were converted to soil mechanical resistance by using the soil resistance curve. Plant growth varied positively with soil air-filled porosity, and negatively with soil mechanical resistance in both tillage systems. However, the decrease rates/increase rates were dependent on the tillage system. The no-tillage system somehow improved the soil physical conditions for the plants, especially when they were more restrictive, allowing them to attain greater values of growth.

Contribution of natural soil compaction on hardsetting behavior

Abstract Many soils in tropical countries present genetically inherited compacted layers, which are commonly referred to as hardsetting. The occurrence of hardsetting is attributable to certain soil physical, chemical and mineralogical properties. We hypothesized that natural soil compaction contributes significantly to the occurrence of a hardsetting behavior in soils from Brazil. The aim of the study was to determine the effect of natural soil compaction on the occurrence of hardsetting horizons of a clayey Yellow Cohesive Latosol. This effect was analyzed: (a) in thin sections and microclods, by determining micropedological features, (b) in soil clods, by measuring tensile strength, and (c) in undisturbed samples, by determining the relationship between penetration resistance and effective stress. The analysis of thin sections and microclods revealed a denser particle packing for the hardsetting horizon. Tensile strength of the clods was significantly higher for the hardsetting horizon, probably due to higher packing of particles. For the variation in effective stress ( σ ′), the increment in penetration resistance (SS) was higher for the hardsetting horizon, which also had a higher bulk density ( D b ). The natural soil compaction was the main factor that, directly or indirectly, influenced the physical and morphological properties analyzed and was responsible for the differences observed between non-hardsetting and hardsetting horizons, confirming the tested hypothesis.

Relações entre propriedades físicas e características de solos da região sul do Brasil

Relacoes funcionais entre atributos dos solos podem ser utilizadas para associar certas propriedades fisicas com caracteristicas desses solos. Este trabalho teve como objetivo determinar as relacoes entre algumas propriedades fisicas dos solos, especificamente densidade do solo (Ds), densidade de particulas (Dp) e capacidade de campo (θCC), ponto de murcha permanente (θPMP) e agua disponivel (θAD) e atributos rotineiramente determinados em levantamentos pedologicos. No estudo, foram utilizados 18 perfis representativos dos solos ocorrentes nos estados do Rio Grande do Sul e Santa Catarina, regiao Sul do Brasil. Foram coletadas amostras deformadas e indeformadas nos horizontes A e B para a determinacao de Ds, Dp, θCC, θPMP e θAD, granulometria, materia orgânica, oxidos de ferro e aluminio. As relacoes obtidas (regressoes multiplas) demonstraram que Ds, Dp, θCC, θPMP e θAD foram influenciadas por um numero reduzido de caracteristicas dos solos, especificamente teores de argila, silte e teor de oxidos de ferro e aluminio. Esses resultados preliminares podem servir para nortear o desenvolvimento de funcoes de pedotransferencia para a regiao Sul do Brasil.

Spatial heterogeneity of soil properties in areas under elephant-grass short-duration grazing system.

Soil properties can be changed by several factors, such as plant roots and animal trampling. The identification of spatial heterogeneity of these properties depends on the sampling scale. This study was developed to test the hypothesis that soil chemical and physical properties beneath elephant-grass plants are different from those between them. The research was carried out in a soil classified as Kandiudalfic Eutrudox. Forty-eight soil samples were collected from 0-10 cm depth (24 beneath plants and 24 between plants). The following properties were measured: pH, organic matter, S, available P, K, Ca and Mg exchangeable, sum of bases, cation exchange capacity, base saturation percentage, dry-aggregate distribution, bulk density and soil penetration resistance. Statistical analyses (t test) indicated that there were no significant differences in soil chemical properties in relation to spatial position. However, significant differences were observed in soil physical properties, with higher values of bulk density and soil resistance to penetration between the plants than beneath the plants.

Estimativa da capacidade de suporte de carga do solo a partir da avaliação da resistência à penetração

A pressao de preconsolidacao, apesar das dificuldades inerentes a sua obtencao, representa uma medida util do estado mecânico do solo para o seu uso, manejo e planejamento de sistemas de mecanizacao. A estimativa da pressao de preconsolidacao, a partir de propriedades do solo facilmente mensuraveis, e, portanto, uma alternativa que pode ser utilizada para contornar as dificuldades. Os objetivos deste trabalho foram: (a) quantificar a pressao de preconsolidacao e a resistencia do solo a penetracao, em laboratorio e em campo, para um Latossolo Vermelho-Amarelo, sob pomar de laranja, e (b) estabelecer a relacao entre ambos os indicadores fisicos. A amostragem e as avaliacoes foram realizadas em oito dias consecutivos, acompanhando o secamento natural do solo. Houve relacao significativa, positiva e linear entre a pressao de preconsolidacao e a resistencia do solo a penetracao, medida no laboratorio e no campo. A similaridade das relacoes entre resistencia a penetracao, obtida no campo e em laboratorio, e a pressao de preconsolidacao permitiu afirmar que a capacidade de suporte de carga pode ser adequadamente estimada a partir da resistencia de um Latossolo Vermelho-Amarelo distrofico a penetracao medida diretamente no campo.

HETEROGENEIDADE DA COMPACTAÇÃO DE UM LATOSSOLO VERMELHO-AMARELO SOB POMAR DE LARANJA

A heterogeneidade na compactacao do solo, provocada por diferentes intensidades de trafego, pode limitar a producao em areas citricolas. O objetivo deste trabalho foi quantificar o indice de compressao (IC) e a pressao de preconsolidacao (sp) nas posicoes de amostragem: linha de plantio, entre rodado, rodado e projecao da copa, para avaliar a heterogeneidade da compactacao de um Latossolo Vermelho-Amarelo distrofico sob pomar de laranja. A amostragem foi realizada em 40 pontos, distribuidos aleatoriamente (10 em cada posicao). Apos saturadas com agua e equilibradas no potencial (y): -10 kPa, as amostras foram pesadas e submetidas ao ensaio de compressao uniaxial com a aplicacao sucessiva e continua de pressoes de 25, 50, 100, 200, 400, 600, 800, 1.000, 1.300 e 1.600 kPa. Os resultados indicaram que a pressao de preconsolidacao mostrou-se mais sensivel do que o indice de compressao na avaliacao da heterogeneidade da compactacao do solo em areas citricolas. A compactacao do solo aumentou no sentido das posicoes de amostragem: linha de plantio, entre rodado, rodado das maquinas e implementos agricolas e projecao da copa das plantas citricas.

Quantificação da resistência tênsil e da friabilidade de um latossolo vermelho distroférrico sob plantio direto

A qualidade estrutural do solo e importante para a emergencia das plântulas, bem como para o crescimento, desenvolvimento e produtividade das culturas. Uma ampla distribuicao de valores de resistencia tensil do solo indica condicoes estruturais do solo para atender a estes pressupostos. O objetivo deste trabalho foi avaliar a resistencia tensil e a friabilidade de um Latossolo Vermelho distroferrico sob plantio direto com sucessao e rotacao de culturas. Os tratamentos utilizados foram: plantio direto com sucessao das culturas de trigo e soja (SDS); plantio direto com rotacao de culturas, utilizando em sequencia milho-aveia-soja-aveia-soja-trigo (SDR), e SDR associado a escarificacao periodica do solo (SDE). Em duas epocas distintas (outubro de 2003 e abril de 2004), foram coletados dez blocos de solo (0,15 x 0,20 x 0,10 m) em cada tratamento na camada de 0-0,20 m de profundidade. Quatrocentos e cinquenta agregados de cada tratamento e epoca de coleta foram utilizados para determinar a resistencia tensil e a friabilidade do solo, determinando-se, tambem, o conteudo de C orgânico. Nao foi verificada influencia do C orgânico do solo na resistencia tensil e na friabilidade do solo. Verificou-se menor resistencia tensil em SDE para o ano de 2003. A sucessao de culturas (SDS) alternou temporariamente a friabilidade do solo entre a classe friavel e a muito friavel. A rotacao de culturas (SDR) manteve temporalmente estavel a estrutura do solo na classe de friabilidade do solo muito friavel, assegurando melhor estrutura e qualidade fisica do solo. A resistencia tensil dos agregados e a friabilidade foram sensiveis na avaliacao da qualidade estrutural do solo para os sistemas de manejo de solo e culturas estudados.

Aggregation agents and structural stability in soils with different texture and organic carbon contents

The flat pampas in the state of Santa Fe in Argentina have soils with high silt content, variable carbon content, and diverse degrees of structural degradation. Aggregate stability has been used as an indicator of the structural condition of the soil. This study aimed to quantify the effect of the addition of crop residues and root activity on the agents of aggregation and mechanisms of aggregate breakdown in soils with different carbon contents and textures cultivated under no-till. An experimental trial was conducted on a loamy soil (Typic Hapludoll, Santa Isabel series) and a silty soil (Typic Argiudoll, Esperanza series) under controlled conditions for 112 days with the following treatments: (i) with and without wheat plant growth and (ii) with and without addition of wheat residues. Soil structural stability by a method allowing for differentiation of aggregate breakdown by slaking, mechanical effect and microcracking, total organic carbon content, particulate organic carbon, glomalin and carbohydrate fractions was assessed. In general, the addition of residues and the presence of plant with active roots increased the presence of all aggregation agents and decreased aggregate breakdown processes in both soils. Soluble carbohydrates and proteins related to glomalin were the most important aggregating agents and their function was to reduce the magnitude of breakdown mechanisms, slaking and microcracking, evidencing a greater impact on the silty soil.