Teógenes Senna de Oliveira

Morpho-physiological responses of cowpea leaves to salt stress

The effect of salt stress of known intensity and duration on morpho-physiological changes in leaves of different ages from cowpea [Vigna unguiculata (L.) Walp.] plants was studied, aiming for a better understanding of the acclimation process of the whole-plant. Seeds were sown in vermiculite and seedlings were transferred to plastic trays containing aerated nutrient solution, and kept in a greenhouse. When the first trifoliate leaf emerged the seedlings were transplanted into 3 L plastic pots containing aerated nutrient solution. Salt additions started 5 d later, and the salt-treated plants received 25 mmol L-1 per day until reaching a final concentration of 75 mmol L-1. During the experimental period primary leaves and the 1st, 2nd, and 3rd trifoliate leaves were used for measurements of net photosynthesis, leaf area, leaf succulence, specific leaf mass, ions and chlorophyll concentrations. Growth analysis of the whole-plant was performed at the end of the experimental period. Salinity did not affect net photosynthesis, but reduced dry mass production and the number of lateral branches. Leaf concentrations of Na+, Cl-, K+ and P increased in salt-stressed plants, but these responses were dependent upon stress duration and leaf age. The higher concentration of potentially toxic ions (Na+ and Cl-) in older leaves could contribute to the reduced ion accumulation in growing tissues, but the tendency of K and P accumulation in leaves appeared to be the result of reduced re-translocation, i.e., not related to plant acclimation. Salinity also increased the source/sink ratio, leaf succulence, specific leaf mass, and chlorophyll accumulation per unit of leaf area, suggesting that the observed changes could be part of an integrated mechanism of whole-plant acclimation to salt stress.

Geochemistry and spatial variability of metal(loid) concentrations in soils of the state of Minas Gerais, Brazil

Since 2009 a policy has been implemented in Brazil to establish the natural concentrations of potentially toxic substances in soil for each state. Historically a mining state, Minas Gerais established a Quality Reference Value for metal(loid)s for all of the soils in the state. To successfully establish these values it is important to study the spatial geochemical diversity for the state. In this context, the objectives of this work are: (1) to evaluate the natural concentrations of metal(loid)s in pristine Minas Gerais soils and (2) to interpret the spatial variability in concentration of these elements. The 0-20 cm layer of soils was sampled for 697 georeferenced sites including the main geological materials and soil groups. Soil properties were analyzed according to methodologies suitable for Brazilian soils. The concentration of metal(loid)s was determined by acid extraction according to EPA 3051A. Descriptive statistics, Pearson correlation and spatial variability analyses were performed. The dominance of acidic pH and low CEC values reflects the pervasive deep acid weathering. The variability of metal(loid) concentrations for soils of the state may be attributed to geological diversity and different pedogenesis. Correlation and spatial analysis indicated that the Fe concentration is strongly associated with metal(loid) concentrations in topsoil. According to the spatial geochemical diversity of the state, a k-means cluster analysis was performed which identified four clusters. A significant difference in the mean values of metal(loid) concentrations between the clusters confirmed that the single Quality Reference Value established does not represent the geochemical diversity of soils in Minas Gerais.

Relationship between magnetization and trace elements content of Brazilian soils from different parent materials

Magnetic minerals are important in some Brazilian soils and they are a possible source of trace elements, especially in the highly weathered soils. The purpose of this investigation was thus to determine the trace element content in the magnetically separated sand, silt, and clay fractions from soils of different lithological origins in order to test the hypothesis that higher levels of magnetization are directly proportional to the contents of these elements. To accomplish this objective, the samples were dissolved by concentrated HCl/HF/HClO 4 acid attack, and the contents of Cd, Cr, Cu, Ni, Pb, Zn, Zr, and V were analyzed by atomic emission spectroscopy with inductively coupled plasma (ICP-AES). The contents of trace elements in the total, magnetic and nonmagnetic sand, silt, and clay fractions were within the normal range presented by whole soils with the exception of Cd, which was higher. Magnetization (σ s ) of the total, magnetic and nonmagnetic soil fractions was evaluated with a special analytical balance. The σ s values were higher for sand and lower for silt and clay fractions. The magnetically concentrated fractions gave results with variation in the same fashion but reaching higher values. The relationship between trace elements in soil fractions and magnetization, studied by correlation analysis, gave higher and more significant correlation coefficients when a soil derived from itabirite was excluded from the analysis. Because itabirite and mafic rocks have high magnetization, the correlation result demonstrates that there is a strongly significant association between magnetization and trace element contents for the soils derived from mafic rocks. Analysis of variance showed that there were significant differences between trace element contents of the magnetic compared with the nonmagnetic fractions of the soils derived from mafic rocks, especially in their sand and silt fractions. Tukeys test for comparison of means showed that mafic rocks have a higher content of trace elements compared with the other parent materials. The results obtained confirm the geochemical affinity of trace elements and the components of the magnetic fraction of the soils derived from the mafic rocks, mainly for sand and silt fractions, where higher contents of the investigated trace elements were observed.

Qualidade de solo sob diferentes usos e manejos no Perímetro Irrigado Jaguaribe/Apodi, CE

A qualidade do solo reflete sua capacidade em atuar de forma positiva na regulagem do fluxo energetico dentro de um agroecossistema. Considerando o impacto da producao agricola nas areas de perimetros irrigados, o objetivo deste estudo foi avaliar a qualidade de um Cambissolo Haplico Eutrofico tipico sob diferentes usos e manejos, no Perimetro Irrigado Jaguaribe/Apodi, CE, Brasil. Os sistemas de producao avaliados foram o de cultivo perene de banana irrigada (CPB) e o de cultivo anual de milho irrigado (CAMI) alem de areas de referencia sob vegetacao natural. Coletaram-se amostras de solo nas camadas entre 0-5, 5-15, 15-25 e 25-40 cm de profundidade, avaliando-se os atributos fisicos (densidade do solo - Ds, densidade de particulas - Dp, condutividade hidraulica - Ks, estabilidade dos agregados em agua) e quimicos (pH em H2O, Ca2+, Mg2+, Na+, K+, COT, NT, CTC a pH 7.0, SB - soma de bases, V - saturacao de bases). A area sob CAMI apresentou maiores impactos negativos sobre Ds, Ks, Dp quando comparada com as dos demais usos, sendo Ds e Ks mais sensiveis na avaliacao do impacto do uso do solo. Os teores de Ca2+, Mg2+, Na+ e K+ foram maiores nas areas cultivadas. Na area cultivada com bananeiras houve reducao nos teores de K+ em funcao, provavelmente, da deplecao deste elemento com a colheita dos frutos . No geral, ocorreu degradacao da qualidade fisica e quimica do solo com o cultivo, resultando na reducao da estabilidade estrutural, na percolacao de agua no solo e em impacto negativo sobre a materia orgânica do solo.

Desenvolvimento do milho sob influência de árvores de pau‑branco em sistema agrossilvipastoril

The objective of this work was to evaluate the effect of pau-branco (Cordia oncocalyx) trees on physiological parameters, height, and biomass of maize at different distances from the trees in an agrosilvipastoral system. The experimental design was a randomized complete block with four treatments (distances from trees of 1, 2, 3, and 4 m), besides a control (plants cultivated in the traditional system), and five replicates. The plots consisted of one pau-branco tree at the center, and maize rows planted at the four evaluated distances from the tree stem. Physiological measurements and dry matter production were recorded at 30, 60, and 90 days after the sowing of maize. The plants under the canopy of pau-branco - at 1 and 2 m from the stem - had their gas exchange, height, and dry matter production affected by the trees. The plants 3 m away from the stem had similar performance to those in the traditional system, and the plants at 4 m of distance had higher photosynthesis, stomatal conductance, transpiration, height, and dry mass production. Maize plants under the canopy are negatively affected by tree shading, whereas plants outside the canopy can be favored by the presence of trees in the system.

Qualidade do solo na cultura do cajueiro anão precoce cultivado sob diferentes sistemas de manejo

Brazil is the most important exporter of cashew nut in the world. The production is concentrated in the northeast region, which accounts for 97 % of the national production. However, in the recent years the cashew nut production has been declining, specially in the state of Ceara, mainly due to inadequate soil management. The aim of this study was to evaluate alterations in the physical and chemical properties of an Ultisol submitted to distinct soil management practices and the development of dwarf cashew trees in a field experiment. The following soil management systems were evaluated: disc harrow + weeding, mechanic mowing + weeding, hand mowing + localized weeding, vegetal cover + localized weeding, vegetal cover + organic residue cover and herbicide use. A split-plot design arranged in randomized blocks was used, considering the different management systems as plots and soil depths as split-plots. Three replications were used. The following soil physical properties were analyzed: granulometry, bulk density, particle density, soil penetration resistance, hydraulic conductivity, soil porosity, as well as chemical properties (exchangeable elements, soil pH, organic matter and phosphorus fractions), and cashew nut yield, plant height and canopy diameter from 1999 to 2002. The management systems that resulted in the most intense soil mobilization and fragmentation of biomass of cover plants (disc harrow, localized weeding and mechanical mowing) favored the degradation of physical and chemical properties, thus reducing the soil quality. Higher and more stable cashew nut yields were obtained in the systems where the practice of removing the vegetation around the trees (localized weeding) had been abandoned, resulting in higher organic matter inputs and absence of soil disturbance. The practice of localized weeding is therefore not recommendable for perennial crops.

Perda de nutrientes por lixiviação em um Argissolo Acinzentado cultivado com meloeiro

This study aimed to evaluate the nutrient losses by leaching as a function of the type of incorporated organic residues into the soil, as well as the accumulation in the melon crop. The experiment was developed in a greenhouse of the UFC/CCA. The soil was a Ultisol, collected in the layer of 0-10 cm. A completely randomized design considering four replications was adopted. The treatments tested were: 0% of organic residues (TEST); 100% of cattle manure (EB); 100% of rice straw (PA) and 50% of cattle manure + 50% of rice straw (EB + PA). The soil bulk density, the nitrogen (total NT, mineral NM and organic NO), total organic carbon (CO), P, K, Ca, Mg and Na in the soil, in the leached water and in the plants were evaluated. The lowest and highest soil bulk density values were found in the PA and TEST treatments, respectively. Nutrients losses by leaching, mainly in relation to P, were observed. The leaching of nutrients seems to be greater in the treatments using cattle manure. The NT and CO losses were not caused exclusively by leaching.

Evaluation of soil physical quality of irrigated agroecosystems in a semi-arid region of North-eastern Brazil

Concern about soil physical quality has grown in recent years, particularly in view of serious problems caused by intensive soil use. We hypothesised that improper soil management in irrigated areas damages the structure of sensitive soils in some regions in North-eastern Brazil. The aim of the study was to evaluate the physical quality of irrigated soils planted with annual and perennial crops, compared with soils under natural vegetation in Ceara State, Brazil. Measurements were made of least limiting water range (LLWR), the S index, and relative density. Undisturbed soil samples were collected at twodepths (5-10 and 20-25cm) in four cultivated areas (banana, guava, pasture, and maize/bean in succession) and two natural vegetation areas (NV1, NV2) adjacent to the cultivated areas. All sites were in the Jaguaribe- Apodi Irrigated District, Limoeiro do Norte, Ceara, Brazil. The LLWR was determined using the water retention curve, soil resistance to penetration, and soil bulk density, which are parameters needed to obtain the upper and lower limits of LLWR. The S index was obtained from the water retention curve. The relative density was obtained from the relationship between bulk density and maximum density obtained from the Proctor test. The S index varied as a function of soil management. The variation in LLWR differed between the studied areas as a function of soil bulk density. The relative densities for NV1 and NV2 were lower than for cultivated areas, showing that intensive soil use has caused compaction. The studied parameters seem to be good indicators of soil physical quality, and it was noticed that soils under cultivation suffer an alteration of their structure relative to soils under natural vegetation.

Soil carbon and nitrogen stocks in traditional agricultural and agroforestry systems in the semiarid region of Brazil

SUMMARY In the semiarid region of Brazil, inadequate management of cropping systems and low plant biomass production can contribute to reduce soil carbon (C) and nitrogen (N) stocks; therefore, management systems that preserve C and N must be adopted. This study aimed to evaluate the changes in soil C and N stocks that were promoted by agroforestry (agrosilvopastoral and silvopastoral) and traditional agricultural systems (slash-and-burn clearing and cultivation for two and three years) and to compare these systems with the natural Caatinga vegetation after 13 years of cultivation. The experiment was carried out on a typical Ortic Chromic Luvisol in the municipality of Sobral, Ceara, Brazil. Soil samples were collected (layers 0-6, 6-12, 12-20, 20-40 and 40-60 cm) with four replications. The plain, convex and concave landforms in each study situation were analyzed, and the total organic C, total N and densities of the soil samples were assessed. The silvopastoral system promoted the greatest long-term reductions in C and N stocks, while the agrosilvopastoral system promoted the smallest losses and therefore represents a sustainable alternative for soil C and N sequestration in these semiarid conditions. The traditional agricultural system produced reductions of 58.87 and 9.57 Mg ha-1

CARBON SEQUESTRATION AND NUTRIENT RESERVES UNDER DIFFERENT LAND USE SYSTEMS 1

This study evaluated the contribution of agroforestry (AFS) and traditional systems to carbon sequestration and nutrient reserves in plants, litter and soil. The study was carried out in the semiarid region of Brazil in a long-term experiment on an experimental farm of the goat and sheep section of the Brazilian Agricultural Research Corporation (Embrapa). Two agroforestry systems were investigated: agrosilvopastoral (ASP) and forest-pasture areas (SP) as well as traditional agriculture management (TM), two areas left fallow after TM (six fallow years - F6 and nine fallow years - F9) and one area of preserved Caatinga vegetation (CAT). Soil, litter and plants were sampled from all areas and the contents of C, N, P, K, Ca and Mg per compartment determined. The AFS (ASP and SP) had higher nutrient stocks than the traditional and intermediate stocks compared to the preserved Caatinga. In the ASP, a relevant part of the nutrients extracted by crops is returned to the system by constant inputs of litter, weeding of herbaceous vegetation and cutting of the legume crops. After fallow periods of six and nine years, carbon and nutrient stocks in the compartments soil, litter and herbaceous plants were similar to those of the preserved Caatinga (CAT), but still lower than under natural conditions in the woody vegetation.