Aim To compare the internal balances of nutrients and the rates of nutrient cycling across nine cocoa agroforestry systems consisting of various combination of soil types (Latosols and Cambisols), production systems (cabruca and Erythrina glauca-shade) and fertilization regimes in southern Bahia, Brazil. Methods We measured nutrient stocks in litter fall production, in the accumulated litter and fruits. The internal nutrient balance for various simulations was obtained by the following expressions:(1) Balance 1=litter -fruit (seeds and husks) and (2) Balance 2=(litter+husks) -seeds. Annual litter decomposition coefficients (k) and subsequent potential of nutrient release were also investigated. The data were analyzed by principal components analysis and by Pearson correlations.

Phosphorus (P) is the main limiting nutritional factor in the cultivation of Eucalyptus in Brazil. Despite this, little is known about the P fractions and dynamics in Eucalyptus soils in tropical regions. The aims of this study were (1) to evaluate the distribution of labile and non-labile fractions of P in soil in 10 sites of Eucalyptus in the state of São Paulo, Brazil and (2) to determine the interactions among the P fractions and to identify which fractions act as sinks or sources for the available P fraction. The P fractions were separated using the Hedley sequential extraction method, and the P transformation processes were evaluated via structural equation modeling. The labile P (resin-Pi + Pi and Po in NaHCO 3 ) varied between 6% and 16%, the moderately labile P (Pi + Po in NaOH) varied between 28% and 40%, the occluded P (Pi + Po in Sonicate + NaOH) varied between 6% and 19%, the P associated with Ca (HCl-Pi) varied between 0.4% and 3% and the residual-P varied between 35% and 47%. The hypothetical structural model of soil P cycle was composed of four P pools (latent variables): the organic pool, occluded pool, inorganic pool, and available pool. The structural model was adequate to identify functional pools of P in soil, and to identify transformation processes of P based on the source-sink relationships. The available P pool was highly dependent on inorganic and occluded pools and the organic pool acted predominantly as a sink of P on available and inorganic pools. The results reinforce the high level of recalcitrance of the organic pool and the fact that Eucalyptus plants must access pools of limited-availability P to meet their nutritional demands.

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Babassu, Attalea speciosa (Arecaceae) is a ruderal palm native to Amazonia, which turned dominant in frequently burned lands throughout the ‘arc of deforestation’ and other degraded lands, in extreme cases attaining complete dominance. This study investigated arbuscular mycorrhizal fungi (AMF) as one possible explanation for the outstanding ecological success of this exceptional palm. We explored the relationships between the babassu palm and native arbuscular mycorrhizal fungi and babassu effects on the AMF richness and mycorrhizal inoculum potential (MIP) in the eastern periphery of Amazonia. For this purpose, we sampled topsoil (0-20 cm) at the onset of the rainy season from a 5-year-old secondary forest regrowth (SEC) area with three levels of babassu dominance (sites with 10, 50 and 70% babassu biomass shares), and at three distances (0, 2.5 and 4 m) from isolated babassu patches within a degraded pasture (PAS), both with five replications per treatment. Glomerospore density varied from 100 to 302 per gram of soil, 56% higher in SEC than PAS. We identified a total of 16 AMF species, with dominance of Acaulospora (six species) followed by Glomus (three species). AMF richness increased with babassu dominance in SEC sites, and reduced with distance from babassu patches within the PAS. The colonization rate of babassu roots was higher in SEC than in PAS, whereas MIP was similar in both areas and without treatment differences. Our study points to strong mycorrhizal association of the babassu palm as a potential mechanism for its outstanding ecological success in degraded lands.

RESUMONos agrossistemas do trópico úmido a variedade e a agressividade das ervas daninhas, são muito grandes, o que dificulta a adoção do plantio direto. Este trabalho foi conduzido com o objetivo de avaliar o efeito de resíduos resultante de diferentes combinações de leguminosas em aléias, sobre a densidade e biomassa de ervas daninhas e alguns atributos do solo. O experimento foi instalado em janeiro de 2002 no campus da Universidade Estadual do Maranhão (UEMA), com as leguminosas: Leucaena leucocephala (Lam.) De Wit.) (leucena), Cajanus cajan (L.) Millsp) (guandu), Clitoria fairchildiana R.A.Howard (sombreiro) e Acacia mangium Willd. (acácia), formando os tratamentos: Sombreiro + Guandu; Leucena + Guandu; Acácia + Guandu; Sombreiro + Leucena; Leucena + Acácia e Testemunha. Utilizou-se o delineamento experimental em blocos ao acaso, com quatro repetições. As amostragens foram realizadas em 2005 e 2007. Foram determinados os teores de N, P, K, Ca, lignina e polifenol nos resíduos, o pH, matéria orgânica, P, K, Ca, Mg, H+Al, densidade, porosidade total e capacidade de aeração no solo, e a abundância e a biomassa das ervas. Concluiu-se que quando as aléias foram combinadas de forma a permitir aplicação de baixa e alta qualidade de resíduos, houve diminuição na ocorrência e agressividade das ervas daninhas, ao mesmo tempo em que foi melhorada a fertilidade do solo.Palavras-chave: atributos físicos e químicos do solo; controle de ervas daninhas; plantio direto; plantas leguminosas. ABSTRACTIn humid tropical land-use systems weed diversity and aggressiveness are extremely high, posing serious limitations to no-tillage agriculture. This paper investigates the effects of combining low-and high-quality organic residues on weed abundance and biomass and selected soil quality indicators. For this purpose, a field experiment was installed in January 2002 on-station at Maranhao State University, comprising four legume species: Leucaena leucocephala (Lam.) De Wit., Cajanus cajan (L.) Millsp, Clitoria fairchildiana R.A.Howard and Acacia mangium Willd., resulting in the following treatments in a completely randomized block design with 4 replications: L.leucocephala + C.cajan; A.mangium + C.cajan; C.fairchildiana + L.leucocephala; L.leucocephala + A.mangium and control (no legumes). Sampling was conducted in 2005 and 2007. We determined weed abundance and biomass, and N, P, K, Ca, lignin e polyphenol contents of the residues. In the topsoil we determined pH, the contents of organic matter, P, K, Ca, Mg, and H+Al, and soil density, total porosity and aeration capacity. We conclude that aggressiveness of weeds can be reduced and at the same time soil fertility can be improved with alley-cropping systems which contain the combination of both high-and low-quality residue producing plants.

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