André Maciel Netto

Condutividade hidráulica não saturada de um podzólico amarelo da zona da mata norte de Pernambuco

The determination of the hydraulic conductivity of a Yellow Podzolic soil was carried out during an experiment in a plot measuring 3.5 m x 3.5 m, at the Estacao Experimental de Itapirema, Goiana, in the State of Pernambuco, Brazil. The internal drainage method was used to obtain the hydraulic conductivity (K(q)) as a function of soil water content, in the three main horizons of the soil. In relation to the methodological aspects, processing of data from internal drainage experiments, including the initial phase of fast drainage, the adjustment of the required parameters, it is necessary to use functions that reproduce the distinct transition between the fast and slow phases of drainage. From all five tested functions, those of power, sum of two exponentials and sum of three exponentials, especially this last one, adjusted well to this distinct transition. Three main horizons of the Yellow Podzolic soil were investigated for hydraulic conductivity. The sandy A horizon, with large pores, has a high conductivity while the BA horizon, with massive structure and few visible pores, has a low infiltration rate. The hydraulic dynamics of the Bt horizon is more complex due to its heterogeneity. The precise characterization of the A and BA horizons, which are the most important to agriculture and soil conservation, makes it possible to elaborate numeric simulation models of the water transference process in the surface horizons of this type of soil.

Reactivity of the plant growth regulator paclobutrazol (cultar) with two tropical soils of the northeast semiarid region of Brazil.

The reactivity of paclobutrazol (PBZ, a plant growth retardant) with a Yellow Ultisol and a Vertisol from the semiarid northeast region of Brazil was evaluated through batch sorption experiments and modeling. Although not instantaneous, the sorption kinetic of PBZ (pure and formulated) was fast (a few hours) in both soils. The sorption kinetics were well described by a second-order (dS(t)/dt=k(2)(S(e2)-S(t))(2)) but not by a first-order model. The sorption isotherms were found to be linear and the calculated K(D) values were 8.8 +/- 0.11 and 7.4 +/- 0.2 L kg(-1) for pure PBZ in the Ultisol and the Vertisol, respectively. The corresponding K(OC) values were 1275 +/- 34 (logK(OC) = 3.11) and 1156 +/- 49 (logK(OC) = 3.06) L kg(-1), respectively. Considering the very different texture of the two soils and the similar K(OC) values determined, these results showed that in both soils, the sorption of PBZ is dominantly controlled by organic matter, although some interactions of PBZ with iron oxides (goethite) were observed in the Ultisol. Based on these sorption parameters a low leachability potential of PBZ in soils is anticipated, as they correspond to a groundwater ubiquity score (GUS) ranging from 2.0 to 2.7, i.e., moderately to not mobile, in contradiction with the actual groundwater situation in Brazil. This work stresses the need to evaluate and predict the risk associated with aquifer contamination by this widely used plant growth regulator.

Transporte do paclobutrazol em colunas de solos

Paclobutrazol (PBZ) is a post-emergence plant growth regulator used in agricultural systems with the objective of vegetative control growth, thereby increasing the reproductive capacity of the plant. This growth regulator remains active in the soil for several years being detrimental to subsequent tillage and contamination of groundwater through leaching. The objective of this work was to study the mechanisms involved in the transport and sorption of PBZ in an Ultisol and a Vertisol, both of the San Francisco Valley, Brazil. Column breakthrough experiments were performed with a water tracer (Bromide) and with PBZ at 0.4 e 1.6 cm3.min-1 in the two soils. Hydrodispersive parameters of both soils were obtained by fitting the tracer breakthrough curves (BTC) with the convection-dispersion (CDE) model, whereas the parameters of PBZ reactive transport were obtained with the CDE-2 sorption sites model, through the CXTFIT code. PBZ presents a lower retardation factor in the Vertisol than in the Ultisol. The water flow was found to strongly affect PBZ mass balance, mainly because of sorption/desorption hysteresis, suggesting partial irreversible sorption of the chemical. The two sites model fitted well the tracer and PBZ breakthrough curves. The results showed that PBZ transport is strongly influenced by its interactions with the soil matrix through rate-limited sorption. The determined transport parameters indicate that PBZ applied to the two tropical soils cultivated with Mango presents an important leaching potential and contamination risk of the groundwater of the San Francisco Valley.

Hydrodispersive characterization of two soils in the irrigated region of São Francisco Valley

The hydrodispersive characterization of a Latosol and a Quartzarenic Neosol, both in the irrigated region of Sao Francisco Valley, was carried out in laboratory by means of assays of displacement of miscible liquids in columns of deformed soil. The assays consisted of the displacement of a pulse of 1.0 volume of pores of the solution of KBr in the outflows of 2.4.10-5, 4.8.10-5, 7.2.10-5, 9.6.10-5 and 1.2.10-4 m3 h-1 and in concentrations of 11.89, 59.49 and 118.99 g L-1, and three repetitions for each assay, under conditions of saturation and flow in stationary condition. By means of program CXTFIT 2.0 that adjusts the analytical solution of the equation of the convection-dispersion (CDE) to the points of the experimental breakthrough curve, it was possible to obtain the hydrodispersive parameters of the retardation factor (R) and coefficient of hydrodynamic dispersion (D). The model CDE carried out a good adjustment to the points of the experimental breakthrough curve, with the values of determination coefficients varying from 98 to 99% for both soils. The values of R are near 1.0 for both the soils, indicating that the KBr does not interact with the soil and the dispersivity of the Neosol is greater than that of the Latosol due to distribution of the size of the pores being greater in the Neosol.The hydrodispersive characterization of a Latosol and a Quartzarenic Neosol, both in the irrigated region of São Francisco Valley, was carried out in laboratory by means of assays of displacement of miscible liquids in columns of deformed soil. The assays consisted of the displacement of a pulse of 1.0 volume of pores of the solution of KBr in the outflows of 2.4.10-5, 4.8.10-5, 7.2.10-5, 9.6.10-5 and 1.2.10-4 m3 h-1 and in concentrations of 11.89, 59.49 and 118.99 g L-1, and three repetitions for each assay, under conditions of saturation and flow in stationary condition. By means of program CXTFIT 2.0 that adjusts the analytical solution of the equation of the convection-dispersion (CDE) to the points of the experimental breakthrough curve, it was possible to obtain the hydrodispersive parameters of the retardation factor (R) and coefficient of hydrodynamic dispersion (D). The model CDE carried out a good adjustment to the points of the experimental breakthrough curve, with the values of determination coefficients varying from 98 to 99% for both soils. The values of R are near 1.0 for both the soils, indicating that the KBr does not interact with the soil and the dispersivity of the Neosol is greater than that of the Latosol due to distribution of the size of the pores being greater in the Neosol.

Determination of hydraulic conductivity and sorptivity of soil using a disk infiltrometer

Determinou-se a condutividade hidraulica e a sorvidade, a partir de dados de infiltracao acumulada, utilizando-se um infiltrometro a disco, em duas camadas de um Neossolo Fluvico (uma superficial, 15 - 25 cm de profundidade, argilosa, e outra 50 - 70 cm de profundidade, arenosa) da vazante do acude Flocos, localizado no municipio de Tuparetama, PE. Para a caracterizacao hidrodinâmica, os ensaios de infiltracao foram realizados aplicando-se potenciais de fornecimento de agua de 0, -3, -6 e -12 cm de coluna de agua, utilizando um infiltrometro a disco, com base de 80 mm de diâmetro. Tres metodos foram empregados para se determinar a condutividade hidraulica (K) e a sorvidade (S) baseados no conhecimento previo da curva de retencao da agua no solo, obtida pelo ajuste das funcionais propostas por: i) van Genuchten (VG); ii) Russo (GR); e iii) Zhang & van Genuchten (ZV) aos valores experimentais de campo e de laboratorio. A equacao da infiltracao acumulada em funcao do tempo descreveu com precisao os ensaios de infiltracao realizados, apresentando coeficientes de determinacao (R2) superiores a 0,995. O metodo GR parece ser o menos recomendado, pois superestima sistematicamente e prediz satisfatoriamente a condutividade hidraulica normalizada para ambas as camadas, enquanto o metodo VG a prediz razoavelmente, para ambas as camadas.

Biodegradação de paclobutrazol por Pseudomonas spp. em sistemas de solo saturados

Paclobutrazol is growth regulator of plants that has low mobility in soil and therefore has accumulated. The objective of this study was to investigate the paclobutrazol biodegradation in two soils from the Sao Francisco River Valley. The biodegradation experiments were conducted in batch using paclobutrazol and paclobutrazol added glycerol. The experiments were performed in sterile and nonsterile conditions using a mixed culture of Pseudomonas. The concentration of paclobutrazol was determined by high performance liquid chromatography. The biodegradation reached 43% in 14 days of experiments with only paclobutrazol and 70% in 28 days of experiments that contained glycerol and paclobutrazol.

Modelagem da cinética de biodegradação de paclobutrazol em dois solos do semiárido do nordeste brasileiro

Mathematical models can help to prevent high levels of toxic substances in soil or fruits of plants treated with pesticides and indicate that such substances should be systematically monitored. The aim of this research was to study the kinetics of paclobutrazol biodegradation by soil native bacteria using mathematical models. Three models were used to assess the kinetics of paclobutrazol biodegradation obtained experimentally. Excellent fits were obtained using dual kinetic and logistic models. The use of glycerol as additional carbon source increased the biodegradation of PBZ and consequently decreased the time required for a given PBZ initial concentration be halved.

FUZZY LOGIC APPLIED TO THE MODELING OF WATER DYNAMICS IN AN OXISOL IN NORTHEASTERN BRAZIL

Modeling of water movement in non-saturated soil usually requires a large number of parameters and variables, such as initial soil water content, saturated water content and saturated hydraulic conductivity, which can be assessed relatively easily. Dimensional flow of water in the soil is usually modeled by a nonlinear partial differential equation, known as the Richards equation. Since this equation cannot be solved analytically in certain cases, one way to approach its solution is by numerical algorithms. The success of numerical models in describing the dynamics of water in the soil is closely related to the accuracy with which the water-physical parameters are determined. That has been a big challenge in the use of numerical models because these parameters are generally difficult to determine since they present great spatial variability in the soil. Therefore, it is necessary to develop and use methods that properly incorporate the uncertainties inherent to water displacement in soils. In this paper, a model based on fuzzy logic is used as an alternative to describe water flow in the vadose zone. This fuzzy model was developed to simulate the displacement of water in a non-vegetated crop soil during the period called the emergency phase. The principle of this model consists of a Mamdani fuzzy rule-based system in which the rules are based on the moisture content of adjacent soil layers. The performances of the results modeled by the fuzzy system were evaluated by the evolution of moisture profiles over time as compared to those obtained in the field. The results obtained through use of the fuzzy model provided satisfactory reproduction of soil moisture profiles.

Potassium adsorption in soil cultivated with sugarcane

Vinasse is a byproduct of the process of distillation of sugarcane juice for the manufacture of sugar and alcohol. Because it is rich in nutrients, mainly potassium (K), is used as fertilizer and applied via fertigation, without concerning for the fate of this compound in the soil. Thus, the objective of the study was to evaluate the interactions of the potassium ion (K+), applied via vinasse in a soil representative of the sugarcane zone of the State of Pernambuco using adsorption isotherms. The methodology was based on physical, chemical and soil mineralogical characterization, as well as equilibrium batch tests, where the experimental curves were fitted by Langmuir and Freundlich isotherm models. The results allowed to infer that the Freundlich model showed better fit of the curve in both forms: linear and non-linear (direct fit); the non-linear model was selected due to the values ​​of coefficient of determination (R²). The interaction between potassium and soil occurred mainly with organic matter and the presence of soil kaolinite, because they showed negative ions on the external surface, thereby promoting potassium adsorption. Soil potassium adsorption capacity was higher for the first layer (0-20 cm) and decreased along the depth profile.

Caracterização hidrodinâmica e hidrodispersiva de um latossolo amarelo na microrregião do brejo paraibano

To model the water flow and solute transport in soils, hydrodynamic and hydrodispersive parameters are required as input data in the mathematical models. The axisymmetric infiltration experiment using a single-ring infiltrometer with a conservative tracer (KCl) is a simple and efficient method for the determination of these parameters in the field. The objective of this study was to characterize hydrodynamic and hydrodispersive parameters of some soils in a marshy region, in Areia-PB, in the field, based on single-ring infiltration tests. The experiments were conducted in an area with common bean, in a 50 x 50 m grid. Saturated hydraulic conductivity (Ks) and sorptivity (S) were estimated by analysis of three- dimensional axisymmetric infiltration for short and long periods. The inert solute (Cl-) was used to calculate the mobile water fraction Φ, by measuring solute concentration in the 0-15 cm layer at the end of the infiltration experiment. A numerical model of solute transfer based on the concept of convection-dispersion (CD) was used to determine the transport parameters (D and R). Single-ring infiltrometry proved to be a simple and efficient method to obtain the hydrodynamic and hydrodispersive parameters. A good agreement was observed between measured and calculated values (v, D and R) with the model CD, based on the coefficients of determination (r2).