Neyde Fabíola Balarezo Giarola

Improvement of a testing apparatus for dynamometry: procedures for penetrometry and influence of strain rate to quantify the tensile strength of soil aggregates

A resistencia do solo a penetracao (RP) e a resistencia tensil de agregados (RT) sao comumente utilizadas para caracterizar a condicao estrutural de solos agricolas. O objetivo deste trabalho foi avaliar a funcionalidade de uma maquina de ensaio para dinamometria mediante a automatizacao do controle de posicao e da velocidade linear de sua base movel nas medicoes de RP e de RT. O equipamento proposto foi utilizado na determinacao da RP em amostras indeformadas de um Nitossolo Vermelho eutroferrico argiloso sob cultivo de seringueira, considerando duas posicoes de amostragem (linha e entrelinha). Nessas amostras tambem foram determinados o teor de agua e a densidade do solo, cujos dados foram utilizados para o ajuste da curva de resistencia do solo a penetracao (CRP). Os valores de RT foram medidos num Latossolo Vermelho distrofico de textura media (LVd) e num Nitossolo Vermelho distroferrico muito argiloso (NVdf) sob distintos sistemas de uso: LVd, sob culturas anuais e mata nativa, e NVdf, sob culturas anuais e mata com eucaliptos ha mais de 30 anos. Quanto as determinacoes de RT, foram utilizadas duas maquinas de ensaio dinamometrico para aplicar distintas taxas de deformacao: uma de referencia (0,03 mm s-1), ja amplamente empregada em outros trabalhos, e o equipamento proposto (1,55 mm s-1). A CRP apresentou elevado valor de coeficiente de determinacao (R2 > 0,9), independentemente da posicao de amostragem. Os valores medios de RT do LVd e do NVdf obtidos com o equipamento proposto nao diferiram (p > 0,05) daqueles da maquina de ensaio de referencia, independentemente do sistema de uso e da classe textural do solo. Os resultados indicam que a RP e a RT podem ser determinadas mais rapidamente e com elevada acuracia utilizando o procedimento proposto.

Temporary effect of chiseling on the compaction of a Rhodic Hapludox under no-tillage

A escarificacao mecânica tem sido empregada para amenizar os efeitos da compactacao em solos manejados sob sistema plantio direto (SPD). No entanto, nao esta clara a duracao dos seus efeitos sobre as propriedades fisicas do solo. O objetivo deste trabalho foi avaliar o comportamento da densidade do solo (Ds) e do grau de compactacao (GC) em profundidade apos a escarificacao do solo sob SPD durante um ano. O experimento localiza-se no municipio de Ponta Grossa, Parana, em um Latossolo Vermelho distrofico. Medidas de Ds e GC foram feitas em area sob SPD por 16 anos (PD) e imediatamente apos a escarificacao (ESC), em maio/2009; seis meses apos a escarificacao (ESC6M), em outubro/2009; e um ano apos a escarificacao (ESC12M), em maio/2010. Nas camadas de 0,0-0,10, 0,10-0,20 e 0,20-0,30 m, verificou-se reducao significativa da Ds em ESC e aumento expressivo em ESC6M. Em ESC12M, constataram-se valores de Ds similares aos medidos antes da mobilizacao do solo. A escarificacao reduziu o GC nas camadas de 0,0-0,10 e 0,10-0,20 m, com o retorno aos valores originais um ano apos a escarificacao. Nos periodos ESC, ESC6M e ESC12M foram observados aumentos da Ds na camada de 0,30-0,40 m, em comparacao com o PD. Os maiores valores de GC foram observados seis meses apos a escarificacao, porem o solo mostrou grande recuperacao estrutural, possivelmente devido ao elevado grau de resiliencia do solo e a influencia dos ciclos de umedecimento e secagem durante o periodo estudado. Os efeitos da escarificacao, avaliados pela Ds e GC, apresentaram duracao inferior a um ano; portanto, possiveis efeitos beneficos da escarificacao em reduzir a Ds em superficie, em curto prazo, propiciam aumento dos riscos de compactacao do solo em profundidade.

Visual soil structure quality assessment on Oxisols under no-tillage system

Methods for evaluation the soil structure quality based on field evaluations are useful to determine strategies for soil management, with the advantage of requirement the use of little equipment and the possibility of immediate interpretation. A new methodology was recently developed to temperate soils for this purpose, called Visual Soil Structure Assessment (Ball et al., 2007). It was tested the hypothesis that it is possible to apply and advance in the interpretation of the results from use of Visual Soils Structure Assessment in cultivated Oxisols. Therefore the goal of this study was to apply, evaluate and enhance the potential of the methodology developed by Ball et al. (2007) in two Oxisols under long-term, no-till in Parana State, Brazil, as well as in a soil under native forest, used as reference of soil structural quality. The proposed implementation and progress in terms of structural quality for the distinct layers provided an assessment of soil physical quality more practical and detailed. This is useful to support the selection of appropriate techniques for mechanical and biological management systems in order to achieve the physical quality of soil suitable for crop development. Visual scores of soil structure quality proposed by Ball et al. (2007) can be applied to Brazilian Oxisols cultivated under no-tillage system.

Permeabilidade ao ar em Latossolo Vermelho sob diferentes sistemas de manejo

A permeabilidade ao ar pode ser utilizada para avaliar alteracoes que ocorrem na estrutura do solo em virtude da adocao de diferentes sistemas de manejo. Este estudo testou a hipotese de que o menor revolvimento do solo sob sistema plantio direto resulta na formacao de poros mais continuos e melhor condicao de aeracao no solo. O objetivo deste trabalho foi avaliar, por meio da permeabilidade ao ar (Ka), da porosidade de aeracao (ea) e dos indices de continuidade de poros (K1 e N), a aeracao em um Latossolo Vermelho distrofico sob preparo convencional (PC) e sistema plantio direto (SPD). Oitenta amostras de solo (2 tratamentos x 2 profundidades x 20 repeticoes) com estrutura indeformada foram coletadas de cada sistema de manejo do solo nas profundidades de 0-0,10 e 0,10-0,20 m em area experimental do Instituto Agronomico do Parana, no municipio de Ponta Grossa, Parana. Depois de saturadas e equilibradas em seis potenciais matricos (-2, -6, -10, -30, -70 e -100 kPa), determinou-se a permeabilidade ao ar e a porosidade de aeracao em cada potencial. Tambem foram determinados a densidade do solo, a densidade de particula, o carbono orgânico e a porosidade. A densidade do solo nao consistiu em fator limitante, ficando abaixo do limite critico para solos argilosos nos dois sistemas. No SPD, o maior volume de microporos resultou em maior retencao de agua no intervalo de umidade avaliado (-2 a -100 kPa) e em maior volume de poros bloqueados para o fluxo de ar (eb), ou seja, reducao de Ka. Na profundidade avaliada (00,20 m), os indices de continuidade de poros (K1 e N) revelaram que o PC apresentou poros mais continuos do que o SPD, contradizendo a hipotese testada.

Desenvolvimento de um consolidômetro pneumático: modelagem da compactação, penetrometria e resistência tênsil de agregados de solo

Soil compaction is one of the processes responsible for soil physical degradation that may result in the loss of sustainability of agricultural production. Therefore, it is important to have instrumental strategies to quantify soil physical properties that are influenced by soil compression and used to assess soil quality. The objectives of this study were to: (i) develop an inexpensive pneumatic consolidometer, (ii) evaluate its functionality by the study of the compressive behaviour of a sandy clay Rhodic Hapludox under no-tillage, (iii) evaluate the potential use of pneumatic propulsion to determine penetration resistance (PR) and tensile strength of aggregates (TS) using the proposed consolidometer. Compression curves based on undisturbed soil sampled in and between rows under black oat were used to evaluate the soil compressive behaviour. Uniaxial compression tests were performed in these samples at a soil water content corresponding to a matric potential of -10 kPa and used to determine the compression index (CI) and preconsolidation pressure (σp) and their correlations with other soil physical properties. PR of undisturbed samples of a sandy loam soil under citrus was determined. Aggregates from two Ultisols were used to determine TS in a hardsetting and a non-hardsetting horizons. Results showed that soil bulk density before the uniaxial compression test was higher (p < 0.05) in-between the black oat rows. The compression curve was sensitive to differences in soil structure between sampling positions, and σp and CI indicated, respectively, higher load support and less susceptibility to compaction (p < 0.05) in-between the black oat rows. The use of pneumatic propulsion did not influence the results of PR and TS. Therefore, the soil compression curve, PR and TS can be determined with the equipment developed in this study.

Mineralogia e cristalografia da fração argila de horizontes coesos de solos nos tabuleiros costeiros

The cohesion of hardsetting horizons of Brazilian soils has been mainly associated to inter-related physical and chemical factors, but an influence of mineralogical and crystallographic properties of clay minerals was also suggested by some researchers. In this study we tested the possibility that clay fraction of hardsetting horizons of soils from the Barreiras sediments of Coastal Tablelands are predominantly kaolinitic and highly crystalline and organized, which can favor a face-to-face arrangement of the crystals. The purpose of this study was to evaluate the crystallographic and mineralogical characteristics of clay minerals in hardsetting soil horizons from the sediment group Barreiras and their contribution to the hardsetting character. One non-hardsetting and five hardsetting horizons were studied along the coastal tableland. A kaolinite sample with high crystallinity degree was also included as reference. All profiles were analyzed for taxonomic classification and location of the horizons of interest. Organic matter and oxides were removed from the samples of the selected horizons. After soil dispersion, the clay fraction was individualized, treated and examined by X-ray diffraction (XRD) to determine the minerals and structure degree of order/disorder, according to the method described by Plancon & Zacarie (1990). The degree of structural organization of the kaolinites of the hardsetting and non-hardsetting horizons was similar to and lower than the kaolinite used as reference. Results indicated that the hardsetting behavior of the studied soils could not be explained by clay packaging.

Soil structure and greenhouse gas production differences between row and interrow positions under no-tillage

No-tillage in Brazil is an efficient agricultural system that improves crop productivity whilst controlling erosion caused to the soil by degradation. However, there is some concern regarding soil compaction. Our objective was to determine whether the function of soil structure in sustaining crop growth was dependent on row and interrow positions in long-term no-tillage. We took soil samples from a field in a commercial farm under long-term no-tillage since 1979 on a clayey Oxisol in Southern Brazil. We assessed soil physical quality using the revised Peerlkamp technique and measured bulk density, air-filled porosity and air permeability of intact soil cores. Samples were incubated to assess in vitro N2O and CO2 production. The soil physical and structural properties showed consistent differences between interrow and row positions, where the properties measured were more favorable. The revised Peerlkamp technique proved as efficient as quantitative parameters in discriminating treatment differences. Overall, soil physical conditions in the interrow were less favourable than in the row. Pore continuity did not vary as regards position. This may explain why row position did not influence in vitro N2O and CO2 production. Soil physical quality under no-tillage system is enhanced, at least in the short term, by superficial disturbances in the row as a result of the action of the coulters of the no-tillage seeder.

Preparo do solo em áreas de produção de grãos, silagem e pastejo: efeito na resistência tênsil e friabilidade de agregados

The understanding and quantification of soil use and management on the soil physical quality are important to develop and select sustainable agricultural systems. The purpose of this study was to evaluate the structural quality of a clayey Brazilian Oxisol under different production and soil tillage systems by measuring the tensile strength (TS) and to quantify aggregate friability (F). The study was conducted in Castro, Parana state, in southern Brazil, using three production systems and seven soil tillage types, in a randomized block design. The following production systems were evaluated: (PS I) - ryegrass for soil cover (winter) and corn for grain production (summer); (PS II) ryegrass for haylage/silage and corn for grain production; and (PS III) - ryegrass for grazing and corn for grain production. Seven types of soil tillage were evaluated in each system: (G1) - plow harrow in winter, depth 0.15 m; (G2) - plow harrow in winter and summer, depth 0.15 m; (Plow) - disk plow, depth 0.20 m; (Laser wing subsoiler) - subsoiler wing tips, to a depth of 0.45 m; (Subsoiler) - subsoiler, depth 0.80 m; (Aerator) - soil aerater Aeromix®; and (NT) - No-tillage, where ryegrass was sown using a double disc and corn with a coulter. From each experimental plot soil blocks (0.20 x 0.15 x 0.07 m) were taken which were broken up by hand in their natural aggregates. Then, the aggregates were air-dried for 24 h and passed through sieves with diameters of 12.5 and 19 mm. Forty aggregates from each block were selected and tested for indirect tension to determine TS and quantify F. TS was influenced by the production systems and soil tillage types. The lowest and the highest TS values were found in the soil under grazing and the NT system, respectively. Friability was less sensitive to differentiate production systems and soil tillage types.

Método de avaliação visual da qualidade da estrutura aplicado a Latossolo Vermelho Distroférrico sob diferentes sistemas de uso e manejo

The increasing demand for assessing soil structure for crop growth has motivated researchers to develop simple and reliable visual indicators to assess soil structure at the field. There are a few records in Brazil indicating the use of visual techniques for assessing soil physical quality. This paper tested the hypothesis that the Visual Soil Structure Quality Assessment methodology developed by BALL et al. (2007) is reliable for identifying the structural quality of tropical and subtropical soils under different soil management systems. Therefore, the overall objective of this paper was to visually identify the structural quality of an Oxisol under forest, crop-livestock rotation and no-till system. The structure evaluation was based on appearance, strength and characteristics of structural units from soil blocks, and was defined by five visual scores from the classification quality. The method allows distinguishing soil quality of the different soil use and management systems from the evaluation of the layer sampled.The increasing demand for assessing soil structure for crop growth has motivated researchers to develop simple and reliable visual indicators to assess soil structure at the field. There are a few records in Brazil indicating the use of visual techniques for assessing soil physical quality. This paper tested the hypothesis that the Visual Soil Structure Quality Assessment methodology developed by BALL et al. (2007) is reliable for identifying the structural quality of tropical and subtropical soils under different soil management systems. Therefore, the overall objective of this paper was to visually identify the structural quality of an Oxisol under forest, crop-livestock rotation and no-till system. The structure evaluation was based on appearance, strength and characteristics of structural units from soil blocks, and was defined by five visual scores from the classification quality. The method allows distinguishing soil quality of the different soil use and management systems from the evaluation of the layer sampled.

Qualidade física de um latossolo vermelho sob plantio direto submetido à descompactação mecânica e biológica

A escarificacao e o uso de plantas de cobertura de inverno tem sido adotados para promover a melhoria dos atributos fisicos do solo relacionados a aeracao. O objetivo deste trabalho foi verificar o efeito das plantas de cobertura de inverno e escarificacao nas propriedades fisicas de um Latossolo Vermelho distrofico, textura argilosa, apos 16 anos em sistema plantio direto. Os tratamentos foram realizados em maio de 2009 e consistiram de: plantio direto (PD), plantio direto com escarificacao mecânica a 0,25 m (PD-E) e plantio direto com descompactacao biologica por meio da cultura do nabo forrageiro (PD-B). O delineamento experimental foi em blocos ao acaso com quatro repeticoes, totalizando 12 unidades experimentais. Dezoito meses apos a aplicacao dos tratamentos, foram coletadas amostras indeformadas de solo em cada unidade experimental, em cinco camadas: 0,0-0,1; 0,1-0,2; 0,2-0,3; 0,3-0,4; e 0,4-0,5 m. Foram avaliados os atributos fisicos do solo: porosidade, densidade do solo (Ds), permeabilidade ao ar (Ka) e indices de continuidade de poros. A Ka foi medida por meio de um permeâmetro de carga constante de ar em nove potenciais matricos (ψm): -0,5; -1; -2; -3; -5; -7; -10; -50; e -100 kPa. Os resultados indicam que os atributos fisicos do solo avaliados nao foram alterados pelo uso de plantas de cobertura e escarificacao. Por outro lado, houve diferencas entre camadas de solo, principalmente entre 0,0-0,1 e 0,1-0,2 m. Na camada de 0,1-0,2 m, a Ds foi maior e a porosidade total e Ka (ψm = -5 kPa) foram menores do que na camada de 0,0-0,1 m. No PD-E, verificou-se que a macroporosidade foi maior na camada de 0,0-0,1 m em comparacao com os outros tratamentos. Os resultados sugerem que o solo estudado submetido aos tratamentos de descompactacao, apos 18 meses, retornou a valores semelhantes aos da testemunha.