Sergio Oliveira Moraes

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.

Critical analysis of the field determination of soil hydraulic conductivity functions using the flux-gradient approach

The determination and the use of soil hydraulic conductivity functions obtained from internal drainage experiments, performed in field soil profiles, using the Darcy–Buckingham flux gradient approach are discussed. Details of the calculation procedures indicate the sensitivity of the methodologies used, and of the most commonly adopted model for K(θ) relations: K(θ)=K0.exp[−γ.(θ0−θ)]. It is shown that the unit total water potential gradient cannot prevail in the whole soil profile during internal drainage after infiltration and that, as a consequence of this assumption, several methods of hydraulic conductivity determination yield K(θ) relations which are depth dependent, even for homogeneous soils. The difficulties of using K(θ) relations in modeling soil water dynamics due to their very strong exponential behaviour are also discussed.

More adequate probability distributions to represent the saturated soil hydraulic conductivity

The saturated soil hydraulic conductivity (Ksat) is one of the most relevant variables in studies of water and solute movement in the soil. Its determination in the laboratory and in the field yields high dispersion results, which could be an indication that this variable has a no symmetrical distribution. Adjustment of the normal, lognormal, gamma and beta distributions were examined in order to search for a probability were density function that would more adequately describe the distribution of this variable. The experiment consisted in determining the saturated hydraulic conductivity, through the constant head permeameter method, in undisturbed samples of three soils of different textures from the central western region of the Sao Paulo State, Brazil, and submitting the results to the statistical tests for identification of the most adequate asymmetrical distribution to represent them. Ksat presented high variability, non normal distribution and lognormal, gamma and beta distributions fit. The lognormal probability density function was the most indicated to describe the variable, due to the verified greater agreement.

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.

Percolação de nitrato em Latossolo Amarelo distrófico afetada pela aplicação de composto de lixo urbano e adubação mineral

The movement of nitrate in soil percolate was evaluated in a field experiment using a Typic Hapludox cultivated with sugarcane and amended with urban compost waste or inorganic fertilizer. The experiment, conducted during the years of 1996/97 and 1997/98, had the following treatments: lime + inorganic fertilization, and control and urban compost waste applied in three levels: 20, 40 and 60 Mg ha-1 (dry weight basis). In the second year (1997/98), the urban compost waste was applied to soil in three levels: 24, 48 and 72 Mg ha-1. The results showed an increased nitrate level in the soil percolate at the 0.3, 0.6 and 0.9 m soil depth as a result of inorganic fertilization and compost waste disposal. Nitrate losses evaluated in the 0-0.9 m soil depth showed pollution potential risks either for the inorganic fertilizer or the compost. In the compost treatments, there was an increase in soil organic N at the soil surface and also in the N-NO3- and N-NH4+ levels at the 0.9-1.2 m soil depth. Annual rates of 24 Mg ha-1 (305 kg ha-1 of total N) did not show evidences of causing any groundwater pollution, according to the values established by the World Health Organization. The risks due to nitrate percolation must be considered when planning rate and frequency of application of this waste to soil, to avoid the possibility of nitrate groundwater pollution. In this case, the soil and soil solution monitoring play fundamental roles in preventing this type of pollution.

Heterogeneidade dos pontos experimentais de curvas de retenção da água no solo

Em uma area de Terra Roxa Estruturada Latossolica de Piracicaba,SP, foram coletadas 250 amostras de solo com estrutura indeformada a profundidade de 25 cm, segundo um espacamento regular de 5 m. As amostras foram submetidas as tensoes de 5xl02; 1x103; 6x103; 1x104 (Funil de Haines) e pressoes de 3x104; 8x104; 3x105 e 1,5x106 Pa (Câmara de Pressao de Richards) para obtencao das relacoes entre potencial matrico e umidade do solo. Assim foram obtidos duzentos e cinquenta valores de umidade a base de massa (variavel dependente) para cada valor de tensao fixado (variavel independente), num total de dois mil resultados experimentais. Utilizaram-se medidas de posicao (moda, mediana e media aritmetica), variabilidade (amplitude total, amplitude interquartil, desvio padrao, coeficiente de variacao, assimetria, curtose e limites de confianca em torno da media aritmetica) e numero de amostras para estimar a media da umidade a um dado nivel de probabilidade, com os seguintes objetivos: a) verificar o quanto as distribuicoes de probabilidade dos valores de umidade para as diferentes tensoes consideradas se afastam da distribuicao normal e, consequentemente, investigar qual a melhor medida de posicao para representar o conjunto; b) quantificar a variabilidade a cada tensao considerada, identificando as mais problematicas no estudo da retencao da agua no solo, ao lado de uma analise da sensibilidade das medidas, atraves do calculo do numero necessario de amostras para estimar a media (desconsiderando-se a dependencia espacial das amostras). A analise dos resultados obtidos permitiu concluir que as umidades as tensoes de 5x102 e 1x103 Pa apresentaram distribuicao com assimetria exagerada e portanto ha que se tomar cuidado com o uso da media aritmetica como medida de posicao. O descarte de amostras-problema, baseado na analise fisica dos resultados, permitiu, no entanto, melhor aproximacao da normalidade para estas tensoes, indicando que se deve sempre dar preferencia a curva completa de retencao de agua no solo e nao apenas a dois ou tres pontos de interesse imediato, como e feito usualmente. As umidades as varias tensoes utilizadas apresentaram baixo coeficiente de variacao (< 10%), quando comparadas a outras medidas de propriedades fisicas do solo.

Sistema de aquisição de dados para equipamento de medida da permeabilidade intrínseca do solo ao ar

The intrinsic permeability or soil air permeability is an important soil property for the identification of changes in soil porous space caused by soil tillage, in estimations of soil properties that are expensive and difficult to be determined in the laboratory, and for the formulation of flux models in cropped and contaminated soils. The purpose of this study was to develop a data acquisition system (electronic module and software) for intrinsic permeability measurement, in laboratory. High precision of the acquisition system was observed in the estimation of this property, with a confidence interval of 9.42 ± 0.085 μm2 (significant at the 5 % level), in a standard soil sample consisting of particles with diameter from 0.25 to 0.106 mm of the sand fraction of a medium texture Yellow Red Latosol. The estimate of soil air intrinsic permeability considering the air dynamic viscosity as a function of temperature was significantly greater than the estimate with fixed air dynamic viscosity at approximately 20 oC. The measurement precision of air permeability in an undisturbed Red Latosol sample was high and similar to that of the standard sample and the estimate of water mass removed from the soil sample (3.27 mg).

Sistema automatizado para aquisição de dados de umidade relativa do ar

Due the importance of the environment in animal and crop production and therefore an appropriate environmental control, the main objective of this work is the construction of an automated system for relative humidity data acquisition, using a controller with reduced dimensions and low cost. Calibration was performed under natural and artificial conditions. The methodology showed results that the system can be used for monitoring this environmental factor.

COMPARAÇÃO DE MÉTODOS DE DETERMINAÇÃO DA CONDUTIVIDADE HIDRÁULICA EM UM LATOSSOLO VERMELHO-AMARELO

The hydraulic conductivity, determined as a function of the volumetric soil water content K(θ), is essential to solve, e.g., drainage problems. However, the results of different methods vary according to the different assumptions. The objective of this study was to compare direct field methods (Instantaneous Profile, Flux and Humidity) and indirect laboratory methods for estimating the hydraulic conductivity as a function of soil water content, K(θ). The experiment was carried out in Piracicaba, State of Sao Paulo (Brazil), with a sandy clay texture Typic Hapludox, from June to August 1999 (low rainfall period). The K(θ) functions derived from different methods were compared using the maximum error and concordance index. It was difficult to determine the K(θ) function at a near-saturation water content, where the error for all methods was highest. The concordance of the unit gradient (Flux and Humidity) and indirect laboratory methods with the Instantaneous Profile method was moderate to low. This shows that the assumption of a unit gradient for a sandy clay texture Typic Hapludox results in erroneous estimates of the K(θ) values, due to the non-homogeneous soil profile.

Scaling of soil hydraulic properties in the evaluation of hydraulic conductivity determination methods

Summary Although the theoretical basis of scaling of hydraulic properties has been developed for ideal similar porous media, it is demonstrated that the same concept is useful even when applied to real situations. When the objective is to compare different methods of determination of an hydraulic property, none of which being a standard method, another soil hydraulic property, evaluated by a reliable method, can be taken as a standard and scaling of both properties allows the desired comparison. This procedure of analysis is applied to hydraulic conductivity determination methods using data of an Haplustox (Yellow-red latosol) soil profile.