Manoel Dornelas de Souza

Gamma-ray-computed tomography to investigate compaction on sewage-sludge-treated soil.

Soil compaction is one of the fundamental parameters to evaluate the environmental impact of agricultural machinery traffic on soils. Compaction causes modifications on soil physical properties such as changes in porosity and structure that are related to soil water movement and gas exchange The objective of this work was to evaluate soil surface sealing after sewage-sludge application, and the influence of agricultural machinery traffic, through computed tomography. A first generation tomograph was used having a 137Cs source and a 3 in x 3 in NaI(Tl) scintillation crystal detector coupled to a photomultiplier tube. Image analysis and tomographic unit profiles could successfully be used for the detection of soil surface sealing and soil compaction due to machinery traffic associated to sewage-sludge application.

Estoques de carbono orgânico e de nitrogênio, pH e densidade de um Latossolo após três aplicações de lodos de esgoto

The high organic matter content in sewage sludge is one of the reasons for its utilization as soil amendment. This study aimed to evaluate the effect of consecutive sewage sludge applications on the amounts of carbon, total and mineral nitrogen, pH, and bulk density in a Latossol. Two soil layers (0-0,1 and 0,2-0,4 m) were evaluated after three corn cultivations in Jaguariuna (Sao Paulo State, Brazil), between 1999 and 2001. The treatments consisted of three consecutive applications of two sewage sludge types, applied at five rates each. The increasing rates of urban sludge from the Franca sewage treatment plant (total applications of 0; 10,284; 20,568; 41,136, and 82,272 kg ha-1) caused significant accumulations of carbon and nitrogen in the top soil layer. The treatments with doses of industrial and urban sludge from the Barueri sewage treatment plant (total applications of 0; 17,405; 34,810; 69,620, and 139,240 kg ha-1) did not significantly affect carbon accumulation in the soil, although in these treatments C additions were 14 % higher than in the other sludge treatment. A significant increase in nitrogen accumulation was observed. Bulk density decreased significantly in the upper layer in response to the increasing application rates of the two sludge types. Soil acidification was observed in both soil layers, which made liming necessary after the second and after the third growing seasons. Leaching of mineral-N to the deeper soil layers was observed.

Gamma-ray computed tomography to characterize soil surface sealing

The application of sewage sludge as a fertilizer on soils may cause compacted surface layers (surface sealing), which can promote changes on soil physical properties. The objective of this work was to study the use of gamma-ray computed tomography, as a diagnostic tool for the evaluation of this sealing process through the measurement of soil bulk density distribution of the soil surface layer of samples subjected to sewage sludge application. Tomographic images were taken with a first generation tomograph with a resolution of 1 mm. The image analysis opened the possibility to obtain soil bulk density profiles and average soil bulk densities of the surface layer and to detect the presence of soil surface sealing. The sealing crust thickness was estimated to be in the range of 2-4 mm.

State-space analysis of soil data: an approach based on space-varying regression models

The assessment of the relationship among soil properties (such as total nitrogen and organic carbon) taken along lines called transects is a subject of great interest in agricultural experimentation. This question has been usually approached through standard state-space methods by some authors in the soil science literature. Important limitations of the mentioned procedures used in practice are pointed out and discussed in this paper, specially those related to the model parameters, meaning and practical interpretation. In the standard state-space approach, based on an autoregressive structure, it does not present any parameters that express the variables relationship at the same point in space, but only at lagged points. Also, its model parameters (in the transition matrix) have a global meaning and not a local one, not expressing more directly the soil heterogeneity. Therefore, the objective here is to propose an alternative state-space approach, based on dynamic (space-varying parameters) regression models in order to avoid the mentioned drawbacks. Soil total nitrogen and soil organic carbon samples were collected on a Typic Haplustox. Samples were taken along a line (transect) located in the middle of two adjacent contour lines. The transect samples, totaling 97, were collected in the plow layer (0-0.20 m) at points spaced 2 meters appart. Results show the comparative advantages of the proposed method (based on an alternative state-space approach) in relation to the standard state-space analysis. Such advantages are related to a more adequate incorporation of soil heterogeneity along the spatial transect resulting in a better model fitting, and greater flexibility of the models building process with an easier interpretability of the local model coefficients.

Geoestatística como suporte ao modelo de simulação de agrotóxico CMLS com validação em colunas de solos

O uso de modelos de simulacao e provavelmente a maneira mais eficiente para predizer o comportamento de agrotoxicos no sistema solo/agua/planta. O modelo de simulacao de destino de agrotoxicos CMLS (Chemical Movement in Layered Soils), foi usado para estudar o comportamento do herbicida tebuthiuron, utilizado na cultura de cana-de-acucar, a partir de uma grade de amostragem composta de 111 pontos amostrais, equi-espacados de 200 m e englobando tres tipos de solo: Neossolo Quartzarenico (RQ), Latossolo Vermelho distroferrico (LVdf) e Latossolo Vermelho distrofico (LVd), texturas media e argilosa. Os 373 pontos avaliados pelo simulador, gerados das amostras da grade original e atraves dos metodos geoestatisticos da variografia e krigagem, produziram valores de profundidade atingida pelo herbicida, apos seis anos de simulacao (1989-1995). Para Neossolo Quartzarenico (RQ), o tebuthiuron, em quatro pontos simulados, apresentou valores de profundidade acima de 43 m e com maximo de 50 m, com uma quantidade de produto permanecendo ainda no solo, proximo a 10% do valor aplicado de 1,1 kg ha-1. Resultados provenientes do ensaio em coluna, usados para a validacao do modelo, mostraram que o mesmo superestimou em 6,66% a profundidade atingida pelo herbicida quando comparado ao valor produzido pela coluna, para o Neossolo Quartzarenico (RQ), e subestimou com valores de 4,5% e 20,0%, para o Latossolo Vermelho distrofico (LVd) e o Latossolo Vermelho-distroferrico (LVdf), respectivamente. Esses dados confirmam, para o Neossolo Quartzarenico(RQ) e o Latossolo Vermelho-distrofico (LVd) a adequacao do modelo, na avaliacao do destino do herbicida.