Efficiency of sulfur application on soybean in two types of Oxisols in Southern Brazil.

Modern agricultural techniques have been increasing the yield of soybean (Glycine max L.) while also causing increasing removal of sulfur (S) from the soil. Besides this, the use of concentrated fertilizers with this element and inadequate soil management, with consequent formation of organic matter with low S concentrations, has been causing frequent symptoms if deficiency in the plats. To assess the effect of S on soybean yield and to establish critical levels of S-SO42- available in the soil, two experiments were conducted over a two-year period in the Parana State, Brazil, in fields containing Typic Haplorthox and Typic Eutrorthox soils, located in the municipalities of Ponta Grossa and Londrina, respectively. The experimental design was randomized blocks with five S rates (0, 25, 50, 75, and 100 kg ha-1) and four replicates. The source used was elementary S with 98% purity. The maximum estimated yields on average for the two years were obtained with application of 49.9 and 63.0 kg ha-1 in the Typic Haplorthox and Typic Eutrorthox soils, for an overall average of 56.4 kg ha-1, with S-SO42- concentrations in the 0-20 cm depth of 16.9, 19.3 and 17.1 mg kg-1, respectively, values higher than the 10 mg kg-1 indicated as the adequate concentration for soybean plant. In turn, at the 21-40 cm depth, the S concentrations were 49.5, 74.2 and 56.4 kg ha-1. The efficiency of the fertilization diminished with increasing S rates, in both soil types, while the greatest yield efficiency was obtained in the plants grown in the Typic Haplorthox soil

Transport on exploding percolation clusters

We propose a simple generalization of the explosive percolation process [Achlioptas et al., Science 323, 1453 (2009)], and investigate its structural and transport properties. In this model, at each step, a set of q unoccupied bonds is randomly chosen. Each of these bonds is then associated with a weight given by the product of the cluster sizes that they would potentially connect, and only that bond among the q-set which has the smallest weight becomes occupied. Our results indicate that, at criticality, all finite-size scaling exponents for the spanning cluster, the conducting backbone, the cutting bonds, and the global conductance of the system, change continuously and significantly with q. Surprisingly, we also observe that systems with intermediate values of q display the worst conductive performance. This is explained by the strong inhibition of loops in the spanning cluster, resulting in a substantially smaller associated conducting backbone.Comment: 4 pages, 4 figure

Ocorrência e caracterização dos danos de Erosomyia mangiferae na cultura da manga do Submédio do Vale do São Francisco.

A alteração no agroecossistema da mangueira, provocada pela expansão das áreas cultivadas na região do Submédio do Vale do São Francisco, tem propiciado condições favoráveis aos problemas fitossanitários, como o surgimento de novas pragas. Em meados de 1993, em um pomar comercial de mangueira, no município de Petrolina-PE, constatou-se a ocorrência de um pequeno díptero atacando os ponteiros e a panícula floral da mangueira identificado como Erosomyia mangiferae Felt (Diptera, Cecidomyiidae). Esta praga foi constatada atacando os tecidos tenros da planta, tais como: brotações e folhas novas, panícula floral e frutos do estádio de "chumbinho". Nas brotações e no eixo da inflorescêcia, observam-se pequenos orifícios, através dos quais há formação de galerias que se tornam necrosadas, apresentando, posteriormente, uma exsudação principalmente nas brotações. Nas folhas novas, ocorrem numerosas pontuações esbranquiçadas, contendo as larvas em seu interior. Estas pontuações, após a saída das larvas, tornam-se escuras e necrosadas, podendo ser facilmente confundidas com manchas fúngicas. Em consequência do ataque no eixo da inflorescência, a panícula floral apresenta uma curvatura de fácil visualização na planta, que caracteriza a presença dessa praga na cultura. Além do ataque no eixo da inflorescência, que pode ocasionar a perda total da panícula floral, E. mangiferae pode, também, danificar individualmente os botóes florais e os frutos recém-formados, provocando a queda dos mesmos.Coordenado por Abel Rebouças São José, Tiyoko Nair Hojo Rebouças, Daniel Nieto Angel, Ivan Vilas Bôas Souza, Nilma Oliveira Dias, Marinês Pereira Bomfim. Trabalhos apresentados no I Simpósio Latino Americano sobre Produção de Manga, 1999, Vitória da Conquista, BA

Micro-bias and macro-performance

We use agent-based modeling to investigate the effect of conservatism and partisanship on the efficiency with which large populations solve the density classification task--a paradigmatic problem for information aggregation and consensus building. We find that conservative agents enhance the populations' ability to efficiently solve the density classification task despite large levels of noise in the system. In contrast, we find that the presence of even a small fraction of partisans holding the minority position will result in deadlock or a consensus on an incorrect answer. Our results provide a possible explanation for the emergence of conservatism and suggest that even low levels of partisanship can lead to significant social costs.Comment: 11 pages, 5 figure

Multi-strata agroforestry system with native amazonian plants cultivated in acid soil.

Multi-strata agroforestry system is mentioned as the most promising option for the sustainable agriculture in infertile upland soil of Central Amazonian. However, studies showed that the sustainability practices are not adopted by the growers in this region. lhe objective of this study was to evaluate the soil fertility and nutritional state of native Amazon plant species grown on a Xanthic Ferralsol in an agroforestry system. Native plants species used were r five of timber species - Hevea brasiliensis (rubber), Ceiba pentandra- (kapok), Jacaranda copa ia (jacaranda), Buchenavia huber (cuiarana) and Trattinicka burserifolia (breu); two palm species - Bactris gasipaes (peach palm) and Euterpe oleracea (assai); and five fruit-bearing species - Rollinia mucosa (biriba), Theobroma cacao (cacao), Theobroma grandiflorum (cupuassu), Couma sorbilis (sorva) and Myrciaria dubia (camu-camu). The results showed that plants from the same ecosystem with acidity tolerance differ significantly in nutrient uptake efficiency and nutritional requirements, indicating the possibility of using appropriate species that can be used in an agroforestry system of central Amazon Region

Armadilha para monitoramento de insetos.

bitstream/CNPMA/5817/1/armadilha_insetos.pd

Fracturing highly disordered materials

We investigate the role of disorder on the fracturing process of heterogeneous materials by means of a two-dimensional fuse network model. Our results in the extreme disorder limit reveal that the backbone of the fracture at collapse, namely the subset of the largest fracture that effectively halts the global current, has a fractal dimension of $1.22 \pm 0.01$. This exponent value is compatible with the universality class of several other physical models, including optimal paths under strong disorder, disordered polymers, watersheds and optimal path cracks on uncorrelated substrates, hulls of explosive percolation clusters, and strands of invasion percolation fronts. Moreover, we find that the fractal dimension of the largest fracture under extreme disorder, $d_f=1.86 \pm 0.01$, is outside the statistical error bar of standard percolation. This discrepancy is due to the appearance of trapped regions or cavities of all sizes that remain intact till the entire collapse of the fuse network, but are always accessible in the case of standard percolation. Finally, we quantify the role of disorder on the structure of the largest cluster, as well as on the backbone of the fracture, in terms of a distinctive transition from weak to strong disorder characterized by a new crossover exponent.Comment: 5 pages, 4 figure