Brivaldo Gomes de Almeida

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.

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.

Condicionadores químicos e orgânicos na recuperação de solo salino-sódico em casa de vegetação

The salinization is degrading Brazilian semi-arid soils, which need to be reclaimed for agricultural utilization. This work aimed to evaluate use of organic and chemical amendments in a Fluvic Entisol having saline-sodic properties in Pernambucos semi-arid region. Soil experiment was conducted in soil columns, with 10 treatments: sheep manure, cow manure, gypsum, synthetic polymer in six concentrations and the control, in randomized block design. The columns were submitted to leaching during 70 days, being analyzed the leachates collected at 7 and 70 days and the soil after leaching. In leachates, the pH, EC and concentration of Na+, K+ and Cl- were determined; in the saturation extract, pH and EC were measured, and Na+ concentration in saturation extract, and exchangeable Na+ and cation exchange capacity (CEC) were determined to calculate exchangeable sodium percentage (ESP). Soil physico-hydric variables were also determined. The data obtained were submitted to variance analysis and to Scott Knott test at 0,05 level of probability. The treatments, especially manures, gypsum and polymer at smaller concentration decreased EC, ESP and soluble Na+, increasing hydraulic conductivity of the soil.

Variabilidade espacial de atributos físicos em solos de vale aluvial no semiárido de Pernambuco 1

Soil physical and hydraulic characteristics are relevant for agricultural management, particularly at irrigation districts. The objective of this study was to evaluate the spatial variability of physical attributes of soil in an alluvial valley in the semiarid region of Pernambuco State, at the Ipanema River Watershed. Statistical techniques and geostatistics were applied to observe the degree of dependence and the spatial variability of soil physical properties, in plots adopted for communal agriculture. The coefficient of variation for the hydraulic conductivity was high, medium for soil resistance to root penetration and for sand, clay and silt. For bulk density, particle density and porosity, however, such coefficient was low. Spatial dependence structures were investigated, with ranges spanning from 135 m, for soil hydraulic conductivity, to 465 m, for silt content. Contour map was produced by kriging interpolation, representing the spatial variability of hydraulic conductivity, which showed moderate spatial dependence. Resistance to root penetration, soil density and particle distribution presented spatial random behavior, for the adopted spatial scale. It was possible to identify regions with higher agricultural potential. From the produced map, it was highlighted that loam soils usually present higher resistance to root penetration, and low hydraulic conductivity.

Comparação de métodos de extração da solução do solo

The ionic composition of the soil solution is of great importance for monitoring the availability of nutrients and fertilizer management, as well as processes of environmental contamination. Thus, the most viable methods to estimate the composition of the soil solution are well accepted in the literature. This study aims to evaluate the performance of the extraction methods by saturation paste, porous extractor cups and soil:water relations of 1:2, 1:5 and 1:10, with and without filtering process. Samples of Fluvic Neossol were used in PVC columns and saturated with solutions corresponding to 0, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110 and 120 mmolc L-1 NaCl, in randomized block design with four replications. The extractors with porous cup are indicated to extract the soil solution for monitoring the electrical conductivity, osmotic potential and ionic composition. The aqueous extract in different soil:water ratio has a potential use for the extraction and subsequent characterization of the aqueous phase of soil. The filtering process can be discarded when the intention is only to determine the electrical conductivity.

Dinâmica de íons em solo salino-sódico sob fitorremediação com Atriplex nummularia e aplicação de gesso

The study was conducted in a saline-sodic Inceptisol from the Cachoeira II Irrigation Perimeter, Serra Talhada (PE), with the objective of evaluating the dynamics of basic cations and anions in a saline-sodic soil subjected to phytoremediation with Atriplex nummularia and correction with application of gypsum. Samples were taken every six months, at four times (0, 6, 12 and 18 months). The experimental design was in randomized blocks, the four Treatments evaluated were: control (without any management practice), chemical correction with gypsum (no crop) and two Atriplex nummularia cultivation (1 x 1 m and 2 x 2 m plant spacing), with four replications. The results of soil analysis revealed the contribution of gypsum application and especially the cultivation of Atriplex plants in reducing the levels of salts in the soil.

CARACTERIZAÇÃO MICROMORFOLÓGICA E CONSIDERAÇÕES SOBRE A GÊNESE DE SOLOS DE TABULEIRO DO SEMI-ÁRIDO DO BRASIL

A detailed macro- and micromorphological investigation was carried out in two Ultisol (Argissolo Amarelo) and one Aridisol (Planossolo Natrico) profile from a tableland surface of the San Francisco river basin in Petrolina, Pernambuco State, Northeastern Brazil. The study aimed to characterize the soils micromorphologically, evaluating their pedogenesis to help understand the soil diversity in the landscape. Results indicate that the three soils were developed from Post-Cretaceous sediments mixed with Pre-Cambrian crystalline rock weathered materials and, also, most probably, with materials from old alluvial terraces of the San Francisco river. The differences among the three profiles were caused by a certain heterogeneity of the parent material but, mainly, due to the soil position in the relief that entailed differences in internal drainage. There occurs a pedogenetic process of iron concretion degradation, inherited from the parent material, to plinthitic mottles, which were, eventually, dissipated in the soil matrix, causing losses from the soil system.

Structural quality of polyacrylamide-treated cohesive soils in the coastal tablelands of Pernambuco

Water-soluble polymers are characterized as effective flocculating agents due to their molecular features. Their application to soils with horizons with structural problems, e.g, a cohesive character, contributes to improvements in the physical quality and thus to the agricultural suitability of such soils. The purpose of this study was to evaluate the structural quality of soils with cohesive horizons of coastal tablelands in the State of Pernambuco treated with polyacrylamide (PAM) as chemical soil conditioner. To this end, three horizons (one cohesive and two non-cohesive) of a Yellow Argisol (Ultisol) were evaluated and to compare cohesive horizons, the horizon of a Yellow Latosol (Oxisol) was selected. The treatments consisted of aqueous PAM solutions (12.5; 50.0; 100.0 mg kg-1) and distilled water (control). The structural aspects of the horizons were evaluated by the stability (soil mass retained in five diameter classes), aggregate distribution per size class (mean weight diameter- MWD, geometric mean diameter - GMD) and the magnitude of the changes introduced by PAM by measuring the sensitivity index (Si). Aqueous PAM solutions increased aggregate stability in the largest evaluated diameter class of the cohesive and non-cohesive horizons, resulting in higher MWD and GMD, with highest efficiency of the 100 mg kg-1 solution. The cohesive horizon Bt1 in the Ultisol was most sensitive to the action of PAM, where highest Si values were found, but the structural quality of the BA horizon of the Oxisol was better in terms of stability and aggregate size distribution.

Water potential in soil and Atriplex nummularia (phytoremediator halophyte) under drought and salt stresses

ABSTRACT Atriplex nummularia is a halophyte widely employed to recover saline soils and was used as a model to evaluate the water potentials in the soil-plant system under drought and salt stresses. Potted plants grown under 70 and 37% of field capacity irrigated with solutions of NaCl and of a mixture of NaCl, KCl, MgCl2 and CaCl2 reproducing six electrical conductivity (EC): 0, 5, 10, 20, 30, and 40 dS m−1. After 100 days, total water (Ψw, plant) and osmotic (Ψo, plant) potentials at predawn and midday and Ψo, soil, matric potential (Ψm, soil) and Ψw, soil were determined. The type of ion in the irrigation water did not influence the soil potential, but was altered by EC. The soil Ψo component was the largest contributor to Ψw, soil. Atriplex is surviving ECs close to 40 dS m−1 due to the decrease in the Ψw. The plants reached a Ψw of approximately −8 MPa. The water potentials determined for different moisture levels, EC levels and salt types showed huge importance for the management of this species in semiarid regions and can be used to recover salt affected soils.

SOLOS FLORESTAIS EM FRAGMENTO DE FLORESTA URBANA NA MATA DE DOIS IRMÃOS, RECIFE, PERNAMBUCO, BRASIL

The forest remnant that composes ‘Parque Estadual Dois Irmaos’ (PEDI) is regarded as one of the largest urban forest fragments in Brazil. There are reports of frequent occurrence of healthy fall trees in the park, in natural conditions, which may compromise its natural balance and its function as an urban forest fragment. Probably, this phenomenon is associated to the chemical and physical properties of the soils comprising PEDI. So, this research aimed to evaluate PEDI soils chemical and physically, identifying, mapping and analyzing the soils in the occurrence of falling tree areas at the research locus. Twelve points of sampling in a representative area of PEDI were mapped, where deformed samples were collected at depths 0-0.10; 0.10-0.30 and 0.30-0.60 m, and not deformed samples at depths 0-0.05 and 0.10-0.15 m. The chemical attributes and part of the physical attributes were determined in the deformed samples. And other physical attributes were determined in the undisturbed samples. The soils of PEDI were low in natural fertility. They have acid reaction and high concentrations of Al 3+ to 0.60 m, and this can create chemical barriers that damage the growth of the plant roots and may be the cause of the frequent tree falling in the park. The soils were classified as clayed to very clayed, very permeable to vertical and lateral water movement. They had high variability in hydraulic conductivity and sharp decrease of water volumetric content in applying small stresses in surface layers as well as higher water retention by soil in Oxisol subsurface. In order to extend the information and create a database for future studies, it is suggested the monitoring of the most vulnerable species to fall, and analyzing other chemical and physical properties of PEDI soils, also opening profiles to understand tap root dynamics.