Desempenho da co-krigagem na determina����o da variabilidade de atributos do solo

A agricultura de precis��o requer princ��pios de manejo de acordo com a variabilidade no campo, exigindo t��cnicas eficientes para estimar e mapear a variabilidade espacial e, ou, temporal das caracter��sticas e propriedades dos solos. Uma an��lise detalhada dos atritubos f��sicos e qu��micos do solo demanda custos e tempo relativamente elevados. Por esse motivo, costuma-se aplicar m��todos estat��sticos de interpola����o para obter as caracter��sticas e propriedades dos solos nos locais n��o amostrados, visando diminuir o n��mero de amostras necess��rias para um bom mapeamento do campo. Algumas vari��veis que caracterizam os atributos de determinado solo s��o, freq��entemente, onerosas e de dif��cil execu����o. Nestas situa����es, �� interessante estimar tais vari��veis com base em outras que apresentam boa correla����o espacial com as primeiras e de simples determina����o. Isto pode ser feito por meio de um semivariograma cruzado. O interpolador que utiliza o semivariograma cruzado em sua modelagem �� chamado de co-krigagem . O objetivo deste trabalho foi investigar a efici��ncia do m��todo estat��stico da co-krigagem na estimativa do pH e do Mn de acordo com a mat��ria org��nica, obtendo as margens de erros associadas a esta t��cnica por compara����o dos valores estimados com aqueles determinados em laborat��rio. Os resultados mostraram que a co-krigagem foi capaz de estimar as variabilidades dos solos com grande exatid��o.

Protective effect of divalent cations against aluminum toxicity in soybean

A large proportion of soybean fields in Brazil are currently cultivated in the Cerrado region, where the area planted with this crop is growing considerably every year. Soybean cultivation in acid soils is also increasing worldwide. Since the levels of toxic aluminum (Al) in these acid soils is usually high it is important to understand how cations can reduce Al rhizotoxicity in soybean. In the present study we evaluated the ameliorative effect of nine divalent cations (Ca, Mg, Mn, Sr, Sn, Cu, Zn, Co and Ba) in solution culture on Al rhizotoxicity in soybean. The growth benefit of Ca and Mg to plants in an acid Inceptisol was also evaluated. In this experiment soil exchangeable Ca:Mg ratios were adjusted to reach 10 and 60 % base saturation, controlled by different amounts of CaCl2 or MgCl2 (at proportions from 100:0 up to 0:100), without altering the soil pH level. The low (10 %) and adequate (60 %) base saturation were used to examine how plant roots respond to Al at distinct (Ca + Mg)/Al ratios, as if they were growing in soils with distinct acidity levels. Negative and positive control treatments consisted of absence (under native soil or undisturbed conditions) or presence of lime (CaCO3) to reach 10 and 60 % base saturation, respectively. It was observed that in the absence of Aluminum, Cu, Zn, Co and Sn were toxic even at a low concentration (25 ��mol L-1), while the effect of Mn, Ba, Sr and Mg was positive or absent on soybean root elongation when used in concentrations up to 100 ��mol L-1. At a level of 10 ��mol L-1 Al, root growth was only reverted to the level of control plants by the Mg treatment. Higher Tin doses led to a small alleviation of Al rhizotoxicity, while the other cations reduced root growth or had no effect. This is an indication that the Mg effect is ion-specific and not associated to an electrostatic protection mechanism only, since all ions were divalent and used at low concentrations. An increased exchangeable Ca:Mg ratio (at constant soil pH) in the acid soil almost doubled the soybean shoot and root dry matter even though treatments did not modify soil pH and exchangeable Al3+. This indicates a more efficient alleviation of Al toxicity by Mg2+ than by Ca2+. The reason for the positive response to Mg2+ was not the supply of a deficient nutrient because CaCO3 increased soybean growth by increasing soil pH without inducing Mg2+ deficiency. Both in hydroponics and acid soil, the reduction in Al toxicity was accompanied by a lower Al accumulation in plant tissue, suggesting a competitive cation absorption and/or exclusion of Al from plant tissue stimulated by an Mg-induced physiological mechanism.

Cation dynamics in soils with different salinity levels growing irrigated rice

Salinity levels in soils of the Outer Coastal Plain of Rio Grande do Sul, Brazil, can be high, due to excess of Na in the irrigation water, evapotranspiration and soil development from marine sediments. The cultivation of irrigated rice could be an alternative, since ion uptake as well as leaching by the establishment of a water layer could mitigate the effects of soil salinity. This study aimed to evaluate the dynamics of basic cations in the solution of Albaqualf soils with different salinity levels growing irrigated rice. The plow layer contained exchangeable Na percentages (ESP) of 5.6, 9.0, 21.2 and 32.7 %. The plant stand, dry matter, Na, K and Ca + Mg uptake at full flowering and grain yield were evaluated. The levels of Na, K, Ca + Mg and electrical conductivity (EC) in the soil solution were also measured weekly during the rice cycle at four soil depths, in the water layer and irrigation water. The Na, K and Ca + Mg uptake by rice at full flowering was used to estimate ion depletion from the layer under root influence. Soil salinity induced a reduction in the rice stand, especially in the soil with ESP of 32.7 %, resulting in lower cation uptake and very low yield at that site. As observed in the water layer and irrigation water, the Na, K, Ca + Mg and EC levels in the soil solution decreased with time at depths of 5, 10 and 20 cm, regardless of the original soil salinity, showing that cation dynamics in the plow layer was determined by leaching and root uptake, rather than by the effect of evapoconcentration of basic cations in the soil surface layer.

Teores de Fe, Mn, Zn, Cu, Ni E Co em solos de refer��ncia de Pernambuco

Metais pesados formam um grupo de elementos com particularidades relevantes e de ocorr��ncia natural no ambiente, como elementos acess��rios na constitui����o de rochas. Esses elementos, apesar de associados �� toxidez, exigem tratamento diferenciado em rela����o aos xenobi��ticos, uma vez que diversos metais possuem essencialidade (Fe, Mn, Cu, Zn e Ni) e benef��cio (Co) comprovados para as plantas. Nesse contexto, o objetivo deste trabalho foi determinar os teores naturais dos metais Fe, Mn, Zn, Ni, Cu e Co nos solos de refer��ncia de Pernambuco. Foram coletadas amostras de solo nas tr��s regi��es fisiogr��ficas (Zona da Mata, Agreste e Sert��o), dos dois primeiros horizontes dos 35 solos de refer��ncia do Estado de Pernambuco. A digest��o das amostras baseou-se no m��todo 3051A (USEPA, 1998), e a determina����o foi efetuada em ICP-OES. Correla����es significativas foram estabelecidas entre os metais e entre estes e a fra����o argila do solo, em ambos os horizontes, indicando a associa����o comum da maioria dos metais com solos mais argilosos. A maioria dos solos apresentou teores de Fe, Mn, Zn, Cu, Ni e Co menores que os de solos de outras regi��es do Pa��s, com litologia mais m��fica, o que corrobora o fato de que os teores desses elementos s��o mais diretamente relacionados aos minerais Fe-magnesianos. Os resultados indicam baixo potencial dos solos de Pernambuco em liberar Cu, Co e Ni para plantas, enquanto defici��ncias de Zn, Fe e Mn s��o menos prov��veis. Os teores naturais de Fe, Mn, Zn, Cu, Ni e Co determinados podem ser utilizados como base para defini����o dos Valores de Refer��ncia de Qualidade para os solos de Pernambuco, de acordo com o preconizado pela legisla����o nacional.

Nitrate role in basic cation leaching under no-till

Especially under no-tillage, subsuface soil acidity has been a problem, because it depends on base leaching, which has been associated with the presence of low molecular weigth organic acids and companion anions. The objective of this study was to evaluate exchangeable base cation leaching as affected by surface liming along with annual urea side-dressing of maize and upland rice. Treatments consisted of four lime rates (0, 1500, 3000, and 6000 kg ha-1) combined with four nitrogen rates (0, 50, 100, and 150 kg ha-1) applied to maize (Zea mays) and upland rice (Oryza sativa), in two consecutive years. Maize was planted in December, three months after liming. In September of the following year, pearl millet (Pennisetum glaucum) was planted without fertilization and desiccated 86 days after plant emergence. Afterwards, upland rice was grown. Immediately after upland rice harvest, 18 months after surface liming, pH and N-NO3-, N-NH4+, K, Ca, and Mg levels were evaluated in soil samples taken from the layers 0-5, 5-10, 10-20 and 20-40 cm. Higher maize yields were obtained at higher N rates and 3000 kg ha-1 lime. Better results for upland rice and pearl millet yields were also obtained with this lime rate, irrespective of N levels. The vertical mobility of K, Ca and Mg was higher in the soil profiles with N fertilization. Surface liming increased pH in the upper soil layers causing intense nitrate production, which was leached along with the base cations.

Surface Complexation Modeling in Variable Charge Soils: Charge Characterization by Potentiometric Titration

ABSTRACT Intrinsic equilibrium constants of 17 representative Brazilian Oxisols were estimated from potentiometric titration measuring the adsorption of H+ and OH− on amphoteric surfaces in suspensions of varying ionic strength. Equilibrium constants were fitted to two surface complexation models: diffuse layer and constant capacitance. The former was fitted by calculating total site concentration from curve fitting estimates and pH-extrapolation of the intrinsic equilibrium constants to the PZNPC (hand calculation), considering one and two reactive sites, and by the FITEQL software. The latter was fitted only by FITEQL, with one reactive site. Soil chemical and physical properties were correlated to the intrinsic equilibrium constants. Both surface complexation models satisfactorily fit our experimental data, but for results at low ionic strength, optimization did not converge in FITEQL. Data were incorporated in Visual MINTEQ and they provide a modeling system that can predict protonation-dissociation reactions in the soil surface under changing environmental conditions.

Surface Complexation Modeling in Variable Charge Soils: Prediction of Cadmium Adsorption

ABSTRACT Intrinsic equilibrium constants for 22 representative Brazilian Oxisols were estimated from a cadmium adsorption experiment. Equilibrium constants were fitted to two surface complexation models: diffuse layer and constant capacitance. Intrinsic equilibrium constants were optimized by FITEQL and by hand calculation using Visual MINTEQ in sweep mode, and Excel spreadsheets. Data from both models were incorporated into Visual MINTEQ. Constants estimated by FITEQL and incorporated in Visual MINTEQ software failed to predict observed data accurately. However, FITEQL raw output data rendered good results when predicted values were directly compared with observed values, instead of incorporating the estimated constants into Visual MINTEQ. Intrinsic equilibrium constants optimized by hand calculation and incorporated in Visual MINTEQ reliably predicted Cd adsorption reactions on soil surfaces under changing environmental conditions.

A POL��TICA DA UNI��O EUROP��IA NO DOM��NIO DA INFORMA����O CIENTIFICO-TECNOL��GICA

Este trabalho visa dar uma panor��mica das pol��ticas da Uni��o Europ��ia no sector da informa����o. Ap��s uma breve introdu����o sobre o empenhamento da UE na passagem �� sociedade da informa����o para aumentar a sua capacidade competitiva diante dos Estados Unidos da Am��rica, descrevem-se v��rios programas europeus que concorrem para esse objectivo

Redes informais nas organiza����es: a co-gest��o do conhecimento

As redes informais nas organiza����es constituem estruturas auto-organizantes que, respondendo em grande parte pela capacidade de as organiza����es lidarem com os problemas imprevistos, configuram-se como instrumentos importantes ao enfrentamento dos desafios associados �� sociedade da informa����o. Este trabalho aborda as redes informais sob a perspectiva do processamento humano da informa����o e do conhecimento que efetuam e dos suportes eletr��nicos de comunica����o que ampliam sua utiliza����o dentro das organiza����es.

Nodula����o e rendimento de soja co-infectada com Bacillus Subtilis e Bradyrhizobium Japonicum / Bradyrhizobium Elkanii

O Bacillus subtilis pode favorecer o desempenho simbi��tico do riz��bio, pelos efeitos na inibi����o de fitopat��genos ou pela exsuda����o de fitorm��nios. Com o objetivo de verificar a viabilidade da co-infec����o de sementes de soja com Bradyrhizobium e Bacillus foram conduzidos tr��s experimentos, no Paran��, em solos com popula����o estabelecida de Bradyrhizobium, em que as estirpes de Bradyrhizobium SEMIA 5019 e SEMIA 5080 e suas variantes tolerantes aos metab��litos de Bacillus foram co-infectadas com duas estirpes de Bacillus (AP-3 e PRBS-1), ou seus metab��litos. Na safra 1993/94, em Londrina, o tratamento de co-inocula����o de Bradyrhizobium com os metab��litos formulados de Bacillus incrementou, significativamente, em rela����o ao n��o-inoculado, o n��mero de n��dulos (59%, est��dio V3), a ocupa����o dos n��dulos pelas estirpes de Bradyrhizobium (76%, R2) e o rendimento de gr��os (24%); em Ponta Grossa, esses incrementos foram de 60%, 145% e 22%, respectivamente. Nessa safra, em Londrina, a co-inocula����o das variantes tolerantes com os metab��litos de Bacillus tamb��m aumentou o rendimento (26%) e N total (17%) dos gr��os de soja e incrementos significativos foram constatados, na ocupa����o dos n��dulos, pela co-inocula����o das variantes tolerantes com as c��lulas de Bacillus (78%). Os resultados obtidos indicam a viabilidade da co-inocula����o, em sementes de soja, de metab��litos brutos ou formulados ou, ainda, de c��lulas de Bacillus subtilis, para incrementar a contribui����o do processo de fixa����o biol��gica do nitrog��nio.

Survival in soil and detection of co-transformed Trichoderma harzianum by nested PCR

The objective of this work was to evaluate the survival of two Trichoderma harzianum co-transformants, TE 10 and TE 41, carrying genes for green fluorescent protein (egfp) and for resistance to benomyl, during four weeks in a contained soil microcosm. Selective culture media were used to detect viable fungal material, whose identity was confirmed by the observation of the fluorescent phenotype by direct epifluorence microscopy. PCR using two nested primer pairs specific to the egfp gene was also used to detect the transformed fungi. Although it was not possible to reliably detect the egfp gene directly from soil extracts, an enrichment step involving selective culture of soil samples in liquid medium prior to DNA extraction enabled the consistent detection of the T. harzianum co-transformants by nested PCR for the duration of the incubation period.

Caracteriza����o de gen��tipos de tomateiro resistentes a begomov��rus por marcador molecular co-dominante ligado ao gene Ty-1

O objetivo deste trabalho foi avaliar gen��tipos de tomateiro, quanto �� resist��ncia a begomov��rus, e caracterizar, por meio do marcador molecular SSR-47, h��bridos de tomate de mesa portadores do alelo de resist��ncia ao begomov��rus Ty-1, com potencial comercial. Os 24 h��bridos experimentais, heterozigotos no loco Ty-1, depois de infectados via enxertia, apresentaram sintomas intermedi��rios, em compara����o aos identificados pelas linhagens homozigotas Ty-1/Ty-1 e pelos gen��tipos suscet��veis Ty-1+/Ty-1+, o que indica a domin��ncia incompleta do alelo Ty-1. Esses h��bridos foram considerados como parcialmente tolerantes a begomov��rus. Os h��bridos experimentais TEX-246, TEX-261, TEX-253, TEX-256, TEX-262, TEX-252, TEX-251 e TEX-268 aliaram m��dias elevadas de produ����o total e de massa m��dia dos frutos; e os h��bridos TEX-246, TEX-253, TEX-256, TEX-262 e TEX-252 apresentaram valores elevados tamb��m para meia-vida da firmeza e foram, portanto, considerados competitivos em compara����o aos padr��es comerciais usados como testemunhas. O marcador molecular SSR-47 foi eficiente em caracterizar gen��tipos portadores do alelo Ty-1. A infec����o do begomov��rus, induzida via enxertia, manifestou sintomas, nos gen��tipos testados, condizentes com os resultados obtidos com o marcador molecular SSR-47.

Rea����es de Etanol com CO/H2 na Presen��a do Sistema Catal��tico Ru(acac)3/I-

The hydrocarbonylation reaction of ethanol with a CO/H2 mixture assisted by Ru(acac)3/iodide was investigated. Bronsted and Lewis acids and iodides salt were used as homogeneous promoters. The etherification reaction was the main reaction under typical acidic conditions of the catalytic system. When a hydrocarbon solvent (toluene) was added to the initial reaction, the alcohol conversion and the carbonylation products were increased. The catalytic activity of the Bronsted acids (conv. EtOH = 71-92%) was higher than that of the Lewis acids promoters (conv. EtOH = 65-85%). The salt present the lower catalytic activity among the promoters used. The long time reaction carried out with ethanol showed an increase of the product selectivity of the homologation and carbonylation reactions while the etherification reaction selectivity decreased. The recycled ether led to 60-65% ethanol conversion to C5 and C6 products. The main catalytic species are H+[Ru(CO)3I3]-, [HRu3(CO)11]- and [HRu(CO)4]-. The first one is active in the carbonylation and homologation reactions of alcohols while the two others take part only in the homologation reaction.

Desenvolvimento e caracteriza����o de recobrimentos de Ni-Co e de seus ��xidos mistos para a produ����o de oxig��nio por eletr��lise alcalina da ��gua

This paper describes the development and characterisation of Ni-Co coatings to be used as anodes in water electrolysis. Chemical oxidation of the surface was performed through thermal treatment at 400��C for 10 h. The resulting surfaces were analysed by X-ray diffraction, EDX, SEM, cyclic voltammetry and constant current electrolysis. The electrochemical oxidation occurring on bare surfaces during electrolysis promotes the formation of thick oxide layers resulting in loss of activity. In oxidised surfaces the chemical Ni-Co oxide grown during the thermal treatment prevents further oxidation thus retaining their activity towards oxygen evolution. An optimum condition for the growth of mixed oxide with high activity was found for the bath containing 50 g L-1 CoSO4.