Rachel Muylaert Locks Guimarães

Tensile strength, friability and organic carbon in an oxisol under a crop-livestock system

O sistema integracao lavoura-pecuaria pode promover a compactacao das camadas superiores do solo, principalmente devido ao pisoteio animal. Porem, o desenvolvimento das plantas e a producao de raizes, em interacao com o pisoteio animal, podem amenizar os efeitos deleterios causados a estrutura do solo por esse sistema. Ate agora, sao desconhecidas as modificacoes fisicas do solo em sistemas de integracao lavoura-pecuaria que utilizam aveia e azevem como forrageiras de inverno para a producao animal. Em funcao disto, o objetivo deste trabalho foi quantificar e relacionar a resistencia tensil, a friabilidade e o teor de carbono orgânico em um Latossolo Vermelho distroferrico sob uso com integracao lavoura-pecuaria. O experimento foi conduzido em Campo Mourao - Parana, Brasil. Quatro tratamentos foram utilizados com alturas de pastejo: 7, 14, 21 e 28 cm. Em cada tratamento foram coletados, casualizadamente, cinco blocos de solo nas profundidades de 0 - 0,10; 0,10 - 0,20 e 0,20 - 0,30 m. O aumento no carbono orgânico do solo promoveu aumentos da resistencia tensil do solo na camada de 0,10 - 0,20 m, sendo verificados nesta camada os maiores valores de resistencia tensil. A friabilidade do solo foi muito friavel com 21 cm de altura de pastejo. Apesar da diminuicao da friabilidade observada nas camadas superficiais, o sistema de integracao lavoura-pecuaria nao e fator limitante aos cultivos anuais subsequentes.

Quantificação da degradação física do solo por meio da curva de resistência do solo à penetração

Soil resistance to penetration (PR) frequently reduces plant root growth. PR increases with soil bulk density (Bd) and decreases with soil moisture (θ), and the mathematical description of the relationships of PR with Bd and θ determines the soil penetration resistance curve (SRC). The objective of this study was to quantify the SRC of an Oxisol under different land use practices and to use it to describe soil physical degradation. Four areas were selected: (a) native forest; (b) pasture cultivated with Brachiaria humidicola for over 20 years; (c) area cultivated with citrus plants for 10 years; and (d) soil under annual crops for 15 years. In each treatment, 48 undisturbed soil samples were collected in the 0-0.10 m layer. Matric potential (Ψ) values from -10 to -15,000 hPa were applied to sets of 16 samples (4 per treatment) to simulate soil drying. The variables PR, Bd and θ of these samples were determined. A non-linear equation was fit to the experimental data to describe SRC (PR = a Bdb θc), in which a, b and c are coefficients of the fitted model. The fitted model explained more than 83 % of the PR variability in all treatments. In compacted soils a higher soil water content is necessary to maintain PR at adequated levels for plant growth (RP < 2.0 MPa). The PR values in soils under annual crops and citrus orchard were excessively high at θ values close to the field capacity (Ψ = -100 hPa), indicating greater soil physical degradation.

Compactação do solo na integração soja-pecuária de leite em Latossolo argiloso com semeadura direta e escarificação

Soil compaction from animal traffic is a concern in crop-livestock systems. This experiment was set up in 2007 with the aim of evaluating the effect of different soil management systems and animal traffic on soil physical and water properties and soybean development and yield. The soil evaluated was a dystrofic Red Latosol (Oxisol) under a no-tillage grain crop system intercropped with forage for the past decade. The effect of animal traffic was evaluated in regard to soil bulk density (Bd), macroporosity (Ma), microporosity (Mi), total porosity (TP), soil resistance to penetration (RP) and soil moisture content (θ), as well as soybean emergence, height and yield. A randomized block experimental design was used with three replications, with the treatments of no-tillage soybean cropping without grazing (SD/SP), no-tillage cropping with grazing in oats (SD/CP) and chisel plowing with grazing (ESC/CP). Soil samples were collected in the 0.00 to 0.07 m, 0.07 to 0.15 m and 0.20 to 0.30 m layers at three time periods: before grazing (August 2007), after grazing (December 2007) and after grazing (October 2008). There was no significant effect of grazing on Bd and TP. At 140 days after sowing of soybean, RP reached values above 2 MPa in the 0.00 to 0.15 m layer in the treatments SD/SP and SD/CP, without limiting crop development. Chisel plowing of the soil in crop-livestock integration under the no-tillage system led to soil physical-water conditions less favorable to plant development. Plant height in the SD/SP was greater than in the treatments SD/CP and ESC/CP, and the lowest grain yield was obtained through chisel plowing of the soil in a year with water deficit.

Intervalo hídrico ótimo para avaliação da degradação física do solo

The effects of soil use and management on soil physical quality have been largely discussed due to its environmental and agronomic impacts. The least limiting water range (LLWR) is a modern indicator of soil physical quality that can indicate processes and mechanisms linked to soil physical degradation caused by soil use and management. The aim of this work was to quantify the influence of different land uses and soil tillage on the LLWR of an Oxisol (170, 40 and 790 g kg-1 clay, silt and sand). Four areas were selected: native forest; planted pasture for more than 20 years; area under citrus cultivation for more than 10 years; area with annual crops (corn, sorghum, oat, and cassava) for 15 years after 10 years of pasture. In each treatment, 48 undisturbed samples were collected in the 0-0.10 m layer. A matric potential of -10 to -15,000 hPa was applied and the soil samples were analyzed for soil bulk density (Bd) , water retention curve, soil resistance curve, LLWR, and critical Bd. Bulk density was influenced by soil use and management at the following sequence commercial crops = citrus > pasture > native forest. The relationship between LLWR and Bd was linear and negative, except under native forest, where the Bd range (1.35-1.55 Mg m-3) had a positive relationship. In the areas under citrus and annual crops, LLWR reached zero, with a critical bulk density (Bdc) of 1.75 and 1.80 Mg m-3, respectively, with severe soil physical degradation. The ratio of these values was 21 % for soil under citrus and 18 % for soil under commercial crops. The loss of soil physical quality was less marked for the soil under pasture than citrus and annual crops, with a less pronounced decrease of LLWR with increasing Bda. The lowest Bd value, at which the reduction of LLWR begins, was named alert bulk density (Bda). The Bd was 1.55 Mg m-3 and can be used as a reference value for the process of soil regeneration, valid for soils with soil texture and soil use and management similar to this study.

Spatial distribution of physical-hydric properties of a nitosols under irrigated bean crop

Devido a utilizacao mais intensa de agua via irrigacao e ao elevado custo que tem sido agregado a este recurso, e necessario que os sistemas de irrigacao operem com altos niveis de eficiencia. A descricao do padrao espacial de propriedades fisico-hidricas do solo pode auxiliar no manejo eficiente da irrigacao. Para tanto, tecnicas da geoestatistica sao necessarias. Assim, este trabalho teve como objetivos descrever e avaliar o padrao espacial da porosidade, densidade e armazenamento de agua no solo durante um ciclo de secamento, num Nitossolo Vermelho distroferrico cultivado com a cultura do feijoeiro. A area de cultivo foi subdividida em 80 quadriculas, segundo uma malha de 3 por 3 m. Em cada quadricula, mediu-se o teor de agua do solo ao longo do tempo, com sondas de TDR de 0,20 m de comprimento, e coletou-se uma amostra de solo indeformada. Os dados foram analisados por meio da estatistica descritiva, analise exploratoria e tecnicas da geoestatistica. A porosidade total, a macroporosidade e a microporosidade ocorreram de forma aleatoria na area. A densidade do solo apresentou moderado grau de dependencia espacial. Verificou-se que a uniformidade de aplicacao da lâmina de irrigacao nao alterou o padrao espacial de armazenamento de agua no solo, evidenciando que fatores intrinsecos do solo definiram este padrao.

Indicators of Soil Physical Quality: From Simplicity to Complexity

In working with soil physics, getting new answers to the same questions is a challenge. As soil physicists, we are always hoping to find new ways of understanding such a complex soil science area. In this chapter, we will discuss some of the ways to assess soil physical quality for crop growth, using ascending complexity classification, from the simplest to the more complex soil physical indicators for crop growth.