Apesar da grande quantidade de N acumulada em plantações de eucalipto de alta produtividade, o aumento em volume do tronco em resposta à aplicação de N não tem sido expressivo nem consistente. O objetivo deste trabalho foi verificar o efeito de doses e fontes de N sobre o crescimento e o acúmulo de N em plantas de eucalipto, na serapilheira, além do impacto nas frações da matéria orgânica do solo (MOS). O experimento foi instalado em campo, no município de Itamarandiba-MG, em blocos ao acaso com três repetições, consistindo da aplicação em cobertura de doses (0, 60, 120 e 240 kg ha-1) e fontes de N distintas (sulfato de amônio e nitrato de amônio) em clone de eucalipto (AEC1528®). O efeito dos tratamentos sobre o crescimento e acúmulo de N nas plantas foi avaliado aos 30 meses de idade, abatendo-se árvores com DAP médio e separando-as em lenho, casca, galhos e folhas, para determinação da produção de matéria seca e dos teores e conteúdos de nutrientes das plantas. Amostras de solo e de serapilheira foram coletadas para análises de nutrientes. Os teores de C e N total da matéria orgânica particulada (MOP) e da matéria orgânica associada à fração mineral (MOAM) foram determinados por espectrometria de massa de razão isotópica, após separação física da MOS. As análises estatísticas consistiram de análise de variância e de regressão. A aplicação de adubos nitrogenados promoveu aumento no crescimento volumétrico do tronco e na matéria seca da parte aérea. A dose de N como sulfato de amônio para obter 90 % da produção máxima foi de 74 kg ha-1, a qual resultou em incremento de 42,3 % no volume de tronco em relação à testemunha sem adubação nitrogenada. Na dose de 120 kg ha-1 de N, não houve diferença de resposta à aplicação de sulfato de amônio e nitrato de amônio. Não foram detectadas alterações nos estoques de C e N da MOS com a adubação nitrogenada. No entanto, houve aumento da absorção de Ca, Mg e S. A taxa de recuperação aparente de N no campo foi maior na dose de 120 kg ha-1 de N, atingindo 34,4 %.

The relationships between plants and endophytic bacteria significantly contribute to plant health and yield. However, the microbial diversity in leaves of Eucalyptus spp. is still poorly characterized. Here, we investigated the endophytic diversity in leaves of hybrid Eucalyptus grandis x E. urophylla (Eucalyptus "urograndis") by using culture-independent and culture-dependent approaches, to better understand their ecology in leaves at different stages of Eucalyptus development, including bacteria with N2 fixation potential. Firmicutes, Proteobacteria (classes alpha-, beta- and gamma-) and Actinobacteria were identified in the Eucalyptus "urograndis" endophytic bacterial community. Within this community, the species Novosphingobium barchaimii, Rhizobium grahamii, Stenotrophomonas panacihumi, Paenibacillus terrigena, P. darwinianus and Terrabacter lapilli represent the first report these bacteria as endophytes. The diversity of the total endophytic bacteria was higher in the leaves from the 'field' (the Shannon-Wiener index, 2.99), followed by the indices obtained in the 'clonal garden' (2.78), the 'recently out from under shade (2.68), 'under shade' (2.63) and 'plants for dispatch' (2.51). In contrast, for diazotrophic bacteria, the highest means of these indices were obtained from the leaves of plants in the 'under shade' (2.56), 'recently out from under shade (2.52)' and 'field' stages (2.54). The distribution of the endophytic bacterial species in Eucalyptus was distinct and specific to the development stages under study, and many of the species had the potential for nitrogen fixation, raising the question of whether these bacteria could contribute to overall nitrogen metabolism of Eucalyptus.

No abstract

Summary Particle‐size distribution (PSD) determines soil C‐saturation; that is, the capacity of the mineral matrix to protect soil organic carbon (SOC) against decomposition. However, the mechanistic connection between PSD and C‐saturation is not entirely clear, especially for Oxisols. To address this issue, we carried out a 12‐month incubation experiment; 13C‐labelled litter inputs equivalent to 0, 4.5, 9.0 and 18.0 mg C g−1 soil were applied to samples of six Brazilian Oxisols, taken from depths of 0–10, 10–20, 20–40 and 60–100 cm. The effect of PSD on SOC protection and C‐saturation was assessed by ‘diluting’ the mass of the clay + silt fraction (< 53 µm) by adding fine sand (150–250 µm) in increments of 0, 20, 40 and 80% relative to the fine earth fraction (< 2 mm). Carbon‐saturation level (CSL) was assumed to be a linear function of clay + silt contents, whereas C‐saturation deficit (CSD) was the difference between the CSL and original SOC content in the samples. After the incubation, litter‐derived C within the clay + silt fraction increased exponentially with CSD. Carbon saturation was indicated by an asymptotic relation between the litter‐derived C in the clay + silt fraction and the additions of litter‐C. For clay + silt contents as small as 15%, CSL was achieved at 61.6 g C kg−1 clay + silt. Conversely, when the proportion of the fraction < 53 µm exceeded 60%, CSL occurred at 33.4 g C kg−1 clay + silt. Thus, a PSD‐dependent hierarchy of SOC protection and C‐saturation in Oxisols can be inferred. Our observations support a conceptual model of C‐saturation where surface interactions provide the dominant mechanism of SOC protection at small clay + silt contents. At large clay + silt contents, physical protection of SOC resulting from the spatial arrangement of fine‐sized minerals defines C‐saturation. Highlights The extent to which particle‐size distribution affects mechanisms that define C‐saturation are unclear. For a clay + silt content of 15%, C‐saturation occurred at 61.6 g C kg−1 clay + silt. When the proportion of the fraction < 53 µm exceeded 60%, CSL occurred at 33.4 g C kg−1 clay + silt. A PSD‐dependent hierarchy of SOC protection and C‐saturation in Oxisols can be inferred.

The eutrophication of aquifers is strongly linked to the mobility of P in soils. Although P mobility was considered irrelevant in a more distant past, more recent studies have shown that P, both in organic (Po) and inorganic forms (Pi), can be lost by leaching and eluviation through the soil profile, particularly in less weathered and/or sandier soils with low P adsorption capacity. The purpose of this study was to determine losses of P forms by leaching and eluviation from soil columns. Each column consisted of five PVC rings (diameter 5 cm, height 10 cm), filled with two soil types: a clayey Red-Yellow Latosol and a sandy loam Red-Yellow Latosol, which were exposed to water percolation. The soils were previously treated with four P rates (as KH2PO4 ) to reach 0, 12.5, 25.0 and 50 % of the maximum P adsorption capacity (MPAC). The P source was homogenized with the whole soil volume and incubated for 60 days. After this period the soils were placed in the columns; the soil of the top ring was mixed with five poultry litter rates of 0, 20, 40, 80, and 160 t ha-1 (dry weight basis). Treatments consisted of a 4 x 5 x 2 factorial scheme corresponding to four MPAC levels, five poultry litter rates, two soils, with three replications, arranged in a completely randomized block design. Deionized water was percolated through the columns 10 times in 35 days to simulate about 1,200 mm rainfall. In the leachate of each column the inorganic P (reactive P, Pi) and organic P forms (unreactive P, Po) were determined. At the end of the experiment, the columns were disassembled and P was extracted with the extractants Mehlich-1 (HCl 0.05 mol L-1 and H2SO4 0.0125 mol L-1) and Olsen (NaHCO3 0.5 mol L-1; pH 8.5) from the soil of each ring. The Pi and Po fractions were measured by the Olsen extractant. It was found that under higher poultry litter rates the losses of unreactive P (Po) were 6.4 times higher than of reactive P (Pi). Both the previous P fertilization and increasing poultry litter rates caused a vertical movement of P down the soil columns, as verified by P concentrations extracted by Mehlich-1 and NaHCO3 (Olsen). The environmental critical level (ECL), i.e., the P soil concentration above which P leaching increases exponentially, was 100 and 150 mg dm-3 by Mehlich-1 and 40 and 60 mg dm-3 by Olsen, for the sandy loam and clay soils, respectively. In highly weathered soils, where residual P is accumulated by successive crops, P leaching through the profile can be significant, particularly when poultry litter is applied as fertilizer.

SUMMARYLarge quantities of poultry litter are being produced in Brazil, which contain appreciable amounts of phosphorus (P) that could be of environmental concern. To assess the immediate environmental threat, five poultry litters composed of diverse bedding material were incubated for 43 days under greenhouse conditions. The litters consisted of: coffee bean husk (CH); wood chips (WC); rice husk (RH); ground corn cobs (CC) and ground napier grass (NG) (Pennisetum purpureum Schum.), in which the change in forms of soluble P was evaluated using 31 P NMR spectroscopy. On average, 80.2 and 19.8 % of the total P in the extract, respectively, accounted for the inorganic and organic forms before incubation and 48 % of the organic P was mineralized to inorganic P in 43 days of incubation. Wide variation in the organic P mineralization rate (from 82 % -WC to 4 % -NG) was observed among litters. Inorganic orthophosphate (99.9 %) and pyrophosphate (0.1 %) were the only inorganic P forms, whereas the organic P forms orthophosphate monoesters (76.3 %) and diester (23.7 %) were detected. Diester P compounds were mineralized almost completely in all litters, except in the CH litter, within the incubation period. Pyrophosphates contributed with less than 0.5% and remained unaltered during the incubation period. Wood-chip litter had a higher organic P (40 %) content and a higher diester: monoester ratio; it was therefore mineralized rapidly, within the first 15 days, achieving steady state by the 29 th day. Distinct mineralization patterns were observed in the litter when incubated with a clayey Oxisol. The substantial decrease observed in the organic P fraction (Po) of

Abstract. Vigorous Eucalyptus plantations produce 105 to 106 km ha−1 of fine roots that probably increase carbon (C) and nitrogen (N) cycling in rhizosphere soil. However, the quantitative importance of rhizosphere priming is still unknown for most ecosystems, including these plantations. Therefore, the objective of this work was to propose and evaluate a mechanistic model for the prediction of rhizosphere C and N cycling in Eucalyptus plantations. The potential importance of the priming effect was estimated for a typical Eucalyptus plantation in Brazil. The process-based model (ForPRAN – Forest Plantation Rhizosphere Available Nitrogen) predicts the change in rhizosphere C and N cycling resulting from root growth and consists of two modules: (1) fine-root growth and (2) C and N rhizosphere cycling. The model describes a series of soil biological processes: root growth, rhizodeposition, microbial uptake, enzymatic synthesis, depolymerization of soil organic matter, microbial respiration, N mineralization, N immobilization, microbial death, microbial emigration and immigration, and soil organic matter (SOM) formation. Model performance was quantitatively and qualitatively satisfactory when compared to observed data in the literature. Input variables with the most influence on rhizosphere N mineralization were (in order of decreasing importance) root diameter > rhizosphere thickness > soil temperature > clay concentration. The priming effect in a typical Eucalyptus plantation producing 42 m3 ha−1 yr−1 of shoot biomass, with assumed losses of 40 % of total N mineralized, was estimated to be 24.6 % of plantation N demand (shoot + roots + litter). The rhizosphere cycling model should be considered for adaptation to other forestry and agricultural production models where the inclusion of such processes offers the potential for improved model performance.

RESUMOCom o incremento exponencial da avicultura no Brasil, a disponibilidade de dejetos de aves e de cama de aviário tem aumentado de maneira semelhante. A proibição de uso desses produtos na ração animal tem feito com que eles sejam direcionados para a produção agrícola como fertilizantes. Ainda há na literatura carência de informação sobre lixiviação de bases no perfil do solo em conseqüência do efeito de ânions inorgânicos acompanhantes, como cloreto, nitrato e sulfato, e do efeito complexante de ácidos orgânicos de baixa massa molecular. O objetivo deste trabalho foi estudar o efeito da aplicação de cama de aviário na lixiviação de Ca, Mg, K e Na em solos e sua associação com ânions inorgânicos e ácidos orgânicos de baixa molecular. Amostras de dois Latossolos Vermelho-Amarelos, um de textura média e outro de textura argilosa, foram colocadas em colunas de PVC constituídas de cinco anéis, cada um com 10 cm de altura e 5 cm de diâmetro, ligados entre si com fita adesiva. O solo colocado no anel superior recebeu, homogeneamente, cinco tipos de camas de aviário: casca de café, casca de arroz, sabugo de milho,