José Flávio Dynia

Nitrate retention and leaching in variable charge soils of a watershed in São Paulo state, Brazil.

Abstract Two Oxisols [Dusky Latosol (LR) and Dark‐Red Latosol (LE)] and one Entisol [Quartzous Sand (AQ)] of a watershed situated at the boundaries of the most important Brazilian aquifer, and intensively cropped to sugarcane, were studied in relation to their nitrate retention and leaching potential, and related electrochemical properties. Nitrate leaching tests carried out with repacked soil columns showed that deep layers of the subsoils, in which electrochemical conditions favor nitrate retention (e.g., net charge near zero, and ZPC larger than pH in water) required a larger number of pore volumes (npv) of leaching solutions for nitrate peak elution and nitrate depletion than surface layers, in which nitrate retention is not favored. Well defined regions of nitrate accumulation were detected in the 220–460 cm layer in the LE and 40–600 cm layer in the AQ. In these regions nitrate concentrations varied from 0.06 to 0.22 and 0.08 to 0.20 cmolc kg‐1, against 0.03 to 0.05 cmolc kg‐1 in the upper and underlayers. Nitrate distribution curves in the LE profile in the years 1995 and 1997 presented similar shapes and positions, indicating that the accumulation region remained almost unaltered, and stationary, in this period. Nitrate accumulation was related to soil electrochemical conditions favorable to nitrate retention.

Disponibilidade de metais pesados para milho cultivado em Latossolo sucessivamente tratado com lodos de esgoto

Apesar do potencial para o uso agricola de lodos de esgoto, seus conteudos de metais pesados podem se tornar um fator limitante a esse uso. Este estudo teve como objetivo avaliar o efeito de diferentes fontes e doses de lodo de esgoto, oriundos das Estacoes de Tratamento de Esgoto de Barueri (LB), que trata esgoto domestico e industrial, e de Franca (LF), que trata esgoto predominantemente domestico, ambas localizadas no Estado de Sao Paulo, sobre os teores de metais pesados em solo e sobre a fitodisponibilidade desses elementos quimicos para o milho. O experimento foi realizado entre os anos de 1999 e 2001, no Campo Experimental da Embrapa Meio Ambiente, em Jaguariuna (SP), em tres cultivos sucessivos de milho, e estudados os seguintes tratamentos, para os dois lodos: testemunha absoluta; adubacao mineral (NPK) recomendada para a cultura do milho; dose dos lodos de esgoto para fornecer uma, duas, quatro e oito vezes a dose de N do tratamento NPK. Foram determinados os teores totais (solo, folha e grao de milho) e disponiveis (solo) de Cu, Mn, Ni, Pb e Zn. O uso de doses crescentes do LB aumentou os teores disponiveis dos metais avaliados em solo, quando se utilizou a solucao de DTPA. Os incrementos nos teores totais de metais pesados foram maiores nas parcelas adubadas com o LB. As solucoes de Mehlich-1 e DTPA mostraram-se eficientes em predizer a fitodisponibilidade de Zn para o milho, quando as folhas e graos foram analisados.

Acúmulo DE Cu, Mn, Ni, Pb E Zn em latossolo vermelho adubado com fontes de lodo de esgoto e cultivado com milho

Realizou-se este estudo com o objetivo de avaliar o efeito das aplicacoes sucessivas, em doses crescentes, de duas fontes de lodo de esgoto sobre os teores totais de Cu, Mn, Ni, Pb e Zn em solo, em tres cultivos sucessivos de milho. O experimento foi conduzido no campo experimental da Embrapa Meio Ambiente, localizado em Jaguariuna-SP, durante os anos agricolas 1999/2000 e 2000/2001, em Latossolo Vermelho Distroferrico. Os lodos utilizados no experimento foram obtidos nas Estacoes de Tratamento de Esgoto (ETEs) de Franca e Barueri. Os tratamentos, para cada fonte de lodo de esgoto, foram os seguintes: testemunha, sem adicao de lodo de esgoto; NPK; aplicacao de lodo de esgoto visando a suprir a quantidade de N normalmente requerida pelo milho; 2; 4 e 8 vezes a dose de lodo aplicada no tratamento 1N. As doses de lodo aplicadas (base seca) variaram de 0 a 139,24 Mg ha-1 para o lodo de Barueri e de 0 a 80,27 Mg ha-1 para o lodo de Franca. Avaliou-se o acumulo de Cu, Mn, Ni, Pb e Zn pela determinacao do teor total (agua regia) desses metais no solo. Os teores totais de Cu e Zn em solo aumentaram com o acrescimo nas doses aplicadas das duas fontes de lodo; contudo, nao foram verificados no solo teores totais dos metais pesados analisados acima dos valores estabelecidos em literatura para solos agricolas.

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.

Effects of liming, green manuring, and phosphate addition on electrochemical attributes of an Oxisol from central Brazil

Abstract Highly weathered tropical soils are characterized by having a predominantly variable charge. Many management practices commonly used in the exploitation of these soils (e.g., liming, phosphate application, and manuring) are known to modify their electrical charge and the sorption/desorption behavior of cations and anions. This process is, at least, partially governed by the charges existing in the soil system. Available information on this subject comes mainly from short‐term laboratory and greenhouse experiments. There is a lack of data regarding the cumulative and long‐term effects of those practices used at farm‐scale levels and on the dynamics and availability of nutrients to the plants under field conditions. In the present work, changes in some electrochemical attributes of a variable charge soil (Oxisol) were studied, as influenced by treatments with phosphate + green manure (Cajanus cajan), phosphate + lime, and phosphate + lime + green manure, applied during a six‐year period. In this pe...