Abstract Litter decomposition restores part of the elements absorbed by the plant back into the soil, acting as a regulator of the biogeochemical cycling of nutrients. This study aimed to evaluate the litter quantity and quality of Eucalyptus grandis in Northern Fluminense region, RJ. Three rotational sequences were studied, the first after 8 years (FR8), the second after 1.5 years (SR2), and a 5year old regrowth (R5). Leaf litter was divided into whole leaves (WL), fragmented pieces (FP), twigs/branches (TB), reproductive structures (RS) and bark (B). The total litter in FR8 was 9.56 Mg ha-1, in SR2, 13.85, and in R5, 22.97 Mg ha-1, corresponding to 83, 163 and 75 kg ha-1 of N, respectively. FP represented 38%, 48% and 55% of N, respectively, in SR2, R5 and FR8. The WL and FP fractions have high recycling potential of organic matter and nutrients due to their lower C/N and Lig/N quality index values.

ABSTRACT The quantification and transfer of nutrient stock among compartments in the forest environment is the key to understanding the nutrient cycling process. The aim of this study was to quantify the nutrient stock and dynamics by litter deposition in a Corymbia citriodora settlement in the Mountainous region of the State of Rio de Janeiro. Different plant parts, deciduous material and litter were chemically analyzed for nutrients. The biomass of trees was 127.23 Mg ha-1, making up about 85.8% of the nutrient stock. On average, the nutrient flux represented 13.6% of nutrients stored in the biomass above the soil. The nutrient cycling process involving N, P, K Ca, and Mg in the long-rotation Corymbia citriodora crop represents an important strategy for maintaining productivity of the forest site.

In this study, we evaluate litter biomass and nutrient inputs, as well as nutrient use efficiency (NUE), in two fragments of dense montane rain forest within the Atlantic Forest Biome in the northern region of the state of Rio de Janeiro, Brazil. The total annual average litter production for the two fragments (designated M1 and M2) was 7.72 and 7.56 t ha−¹ year−¹, respectively. The annual nutrient return rate was 146.67, 4.84, 21.41, 64.93, and 17.25 kg ha−¹ year−¹ for N, P, K, Ca, and Mg, respectively. No differences in NUE were observed between the studied fragments, except for that of P. The average NUE for N, P, K, Ca, and Mg, respectively, was 51, 1426, 367, 111, and 428 in fragment M1, compared with 51, 1890, 360, 126, and 472 in fragment M2. The litter biomass input did not differ between the forest fragments studied, indicating that the differences in elevation and forest biomass did not affect nutrient cycling. However, a difference in the litter deposition rate between the dry and rainy periods was observed in fragment M2.

Os estudos sobre balanço de C e nutrientes em florestas naturais permitem avaliar possíveis alterações decorrentes de técnicas de manejo aplicadas e possibilitam inferir a sustentabilidade dessas florestas. Os objetivos deste trabalho foram avaliar o teor de nutrientes de espécies nativas e quantificar a biomassa (parte aérea + serapilheira) e os estoques de C e nutrientes em fragmentos florestais montanos da Mata Atlântica (Floresta Ombrófila Densa Montana) na região norte do Estado do Rio de Janeiro, no período de maio de 1999 a abril de 2001. Foram selecionados dois fragmentos, localizados a 900 e 600 m de altitude, na vertente atlântica do Parque Estadual do Desengano, RJ. O solo de ambos os fragmentos florestais foi classificado como Cambissolo Háplico Tb distrófico. O valor médio de biomassa (parte aérea + serapilheira) foi de 166,8 Mg ha-1. Em consequência, a acumulação média de C na vegetação foi de 67, 2 Mg ha-1. Os estoques médios de N, P, K, Ca e Mg na vegetação foram de 1.152, 44,4, 276,5, 603,5 e 127,9 kg ha-1, respectivamente. Por outro lado, as espécies revelaram distinta capacidade de estoque de nutrientes. O balanço negativo de P, K e Ca {solo - (parte aérea + serapilheira)} indica que esses elementos constituem principais fatores nutricionais limitantes ao crescimento dos fragmentos florestais montanos da Mata Atlântica na região norte-fluminense.

Nutrient balance in tropical forest allows an evaluation of eventual differences due to management practices and conclusions on forest sustainability. The aim of this study was to evaluate the nutrient concentration in native species and quantify biomass production and C and nutrient balance in tropical montane Atlantic Forest fragments (Dense Montane Ombrophile Forest) in the North of Rio de Janeiro State, from May 1999 to April 2001. Two sites were selected in the State Park of Desengano, at 900 and 600 m asl. The soil of both forest fragments was classified as Dystrophic Haplic Cambissol. The biomass production (above ground + accumulated litter) was 166.8 Mg ha-1. Consequently, the C accumulation was 67.2 Mg ha-1. The mean N, P, K, Ca and Mg pools were 1,152, 44.4, 276.5, 603.5 and 127.9 kg ha-1, respectively. However, at each forest site, the species differed in nutrient pools. The negative balance {soil - (above ground + litter)} of P, K and Ca indicated that these elements were the most limiting to the growth of montane forest fragments at the study sites.

Os solos tropicais muito intemperizados possuem, de modo geral, baixa disponibilidade de P para as plantas e elevada capacidade de adsorção de P inorgânico (Pi). Dessa forma, a manutenção de fontes orgânicas, capazes de suprir P por mineralização, é de grande importância para o crescimento de plantas em condições de acentuado intemperismo. A reciclagem de resíduos orgânicos e a habilidade da comunidade vegetal em conviver com baixas concentrações de P no solo garantem a sustentabilidade em ecossistemas naturais. O objetivo deste trabalho foi estimar o conteúdo de P orgânico (Po) total e as frações lábeis de P no solo, em duas florestas naturais (sítio 1 a 900 m de altitude e sítio 2 a 600 m), em um povoamento de Corymbia citriodora (sítio 3 a 250 m de altitude) e em pastagens adjacentes a cada cobertura florestal, em cada sítio. A taxa de recuperação de Pi + Po em relação à extração nitro-perclórica do P total variou de 50 a 82 %. O teor médio de Po total nos solos florestais foi de 160 mg kg-1 e, nos solos sob pastagem, de 69,8 mg kg-1. A maior diferença de Po total, entre floresta e pastagem, ocorreu no sítio 1 (-74 %), seguido do sítio 3 (-53 %) e sítio 2 (-25 %). O Po representou de 14,6 a 36,9 % do P total extraído. Em relação ao P lábil, o Po representou mais de 80 % nos solos sob florestas naturais e 65 % no solo sob eucalipto. O Po (total e lábil) correlacionou-se positivamente com o C orgânico, e o Po lábil com o P disponível.

Highly weathered tropical soils have low P plant availability and very high inorganic phosphorus (Pi) adsorption capacity. Therefore, maintenance of organic sources able to supply P by mineralization is essential for P availability under highly weathered conditions. Organic matter cycling and tolerance to low P soil concentration of the plant community may guarantee sustainability in natural ecosystems. The aim of this study was to evaluate organic phosphorus (Po) content and labile P fractions in the soils of three sites. The first site was a natural forest at 900 m asl, the second natural forest at 600 m asl and the third a Corymbia citriodora stand at 250 m asl. The same P fractions were evaluated in pasture areas adjacent to each site. The recovery rate of Pi + Po ranged from 50 to 82 % of the nitric-perchloric extraction. Mean total Po in the forest was 160 mg kg-1 and in pasture soil 69.8 mg kg-1. The greatest difference between forest and pasture was observed at site one (-74 %), followed by site three (-53 %) and site two (-25 %). Organic P accounted for 14.6 to 36.9 % of the total extracted P. Labile Po accounted for over 80 % of the total labile P in the natural forests and 65 % in the Corymbia citriodora plantation. Total and labile Po were positively correlated with organic C, and the labile Po was positively related to available P.

Os biossólidos têm sido estudados como fonte de matéria orgânica na agricultura. Objetivou-se avaliar o desenvolvimento de mudas de Acacia mangium e Acacia auriculiformis em diferentes substratos: a) horizonte Bw com areia lavada (1:1, v:v) e adubação mineral de 160, 640 e 160 g m-3de N, P2O5 e K2O, respectivamente (HB); b) horizonte Bw com areia lavada e esterco bovino (1:1:1, v:v) (HBE); c) horizonte Bw com areia lavada e lodo de esgoto (1:1:1, v:v) (HBL); e d) 100% de lodo de esgoto (LE). Aplicou-se 1 kg de CaCO3 p.a. por m³ de substrato. Foram utilizadas sementes inoculadas com rizóbio e não-inoculadas, determinando-se, aos 90 dias após a semeadura, a altura das plantas, o diâmetro do colo e o peso da matéria seca da raiz e da parte aérea, na qual se determinaram N, P, K, Ca e Mg. O delineamento estatístico foi inteiramente casualizado, no esquema fatorial 2 x 4 (com ou sem inoculação x 4 substratos). No LE com inoculação, obteve-se melhor crescimento das mudas. O HBE produziu efeito superior no desenvolvimento das mudas em relação àquele com a mesma proporção de material orgânico na forma de lodo (HBL). Na maioria dos parâmetros avaliados não houve diferença devido à inoculação dos substratos HBE, HBL e HB, provavelmente devido à existência de bactérias nativas nesses substratos. As mudas desenvolvidas no substrato LE foram as que acumularam mais N e Ca, principalmente quando inoculadas. Houve tendência de maior acúmulo de P, K e Mg na parte aérea das mudas desenvolvidas no substrato HBE.

Sewage sludge has been studied as source of organic matter on seedling production. Thus, this study aimed to evaluate the development of Acacia mangium and Acacia auriculiformis seedlings in the following substrates: a) oxic horizon + sand (1:1, v:v) + 160, 640 e 160 g m-3 of N, P2O5 and K2O respectively (HB); b) oxic horizon + sand + cattle manure (1:1:1, v:v) (HBE); c) oxic horizon + sand + sewage sludge (1:1:1, v:v) (HBL) and; d) 100% sewage sludge (LE). The substrates were limed with 1 kg m-3CaCO3 p.a.. Seeds, inoculated and non-inoculated with Rhizobium, were used, and 90 days after planting, measures of collar diameter, plant height, and root and shoot dry matter (with determination of N, P, K, Ca and Mg) were taken. The experimental design was completely randomized blocks, in a factorial 2 x 4 arrangement (with or without inoculation x 4 substrates). Better performance in seedling growth was obtained in the LE substrate with inoculated seeds. Comparatively, the HBE substrate was superior to the HBL substrate. There were no significant differences for most evaluated parameters in the HBE, HBL and HB substrates due to inoculation, probably because the existence of native bacteria in these substrates. The seedlings developing in the LE substrate accumulated more N and Ca, mainly when inoculated. There was a tendency of larger P, K and Mg accumulation in shoots of seedlings developing in the HBE substrate.

A ciclagem de nutrientes em povoamentos de eucalipto permite avaliar possíveis alterações decorrentes de técnicas de manejo aplicadas e possibilita inferir sobre a sustentabilidade das plantações. O objetivo deste trabalho foi estudar a ciclagem de nutrientes e o balanço nutricional em povoamentos de Eucalyptus grandis em primeira rotação (8 anos de idade) e em sistema de rebrota (1,5 e 5 anos) na região Norte Fluminense, no período de janeiro a dezembro de 2001. Determinaram-se a biomassa e o conteúdo de nutrientes da parte aérea (folha, galho, casca e lenho) e da serapilheira depositada e acumulada. Efetuou-se o balanço de nutrientes no sistema solo-serapilheira-parte aérea. O talhão de 8 anos apresentou maior diâmetro, área basal e volume de tronco. Por conseguinte, a biomassa e o conteúdo de nutrientes nesse componente foram superiores aos de outros talhões. A produção total de serapilheira e o fluxo anual de nutrientes no sistema planta-solo foram maiores no talhão em primeira rotação. O folhedo representou a maior contribuição para a deposição de nutrientes ao solo, e o balanço de nutrientes foi positivo em todos os talhões avaliados. Entretanto, houve baixa produção de biomassa, especialmente no talhão em primeira rotação, apesar de as reservas de nutrientes do solo permitirem maior produtividade.

Nutrient cycling in eucalypt stands allows the evaluation of changes due to management and to make inferences about plantation sustainability. The objective of this study was to evaluate the nutrient cycling in eucalypt (Eucalyptus grandis) in Northern Rio de Janeiro State, Brazil. The evaluation was carried out from January to December 2001, in 8-year-old stands and 1,5 and 5 year old coppicing (second rotation). The biomass and nutrient contents of the aerial part (leaf, branch, bark and bolewood), the litterfall and litter were determined. The nutrient balance in the soil-litter-aboveground system was measured. The 8-year-old stand presented the highest DHB (diameter at breast height), section area and tree trunk volume. Consequently the biomass and the nutrient content in this component were higher than in the other stands. Litterfall production was larger in the 8-year-old stand. The nutrient annual flow in the plant-soil system was larger in the 8-year-old stand. Leaf litterfall was the component that contributed the most to nutrient deposition on the soil. Nutrient balance was positive in all stands evaluated. Despite the fact that the soil nutrient resources allows for larger productivity, a low biomass production was found, particularly in the 8-year-old stand.