RESUMO -Este trabalho objetivou quantificar a biomassa e os nutrientes, bem como os efeitos na produtividade e no sítio, de acordo com a intensidade de colheita, em povoamento de Eucalyptus dunnii com 4 anos, em Alegrete, RS. Realizou-se um inventário da unidade amostral para a caracterização dendrométrica do povoamento. As árvores foram compartimentalizadas em raiz, madeira do tronco, casca do tronco, galhos e folhas. Amostras foram retiradas e analisadas quanto aos teores de nutrientes. A biomassa arbórea total foi de 121,9 Mg ha -1 , apresentando a seguinte ordem de distribuição dos componentes: madeira do tronco > raiz > galhos > casca do tronco > folhas. Em termos totais, na biomassa acima do solo, observaram-se 985 kg ha -1de macronutrientes e 32,5 kg ha -1 de micronutrientes, distribuídos em: N (24%), P (2%), K (23%), Ca (34%), Mg (13%) e S (4%) e em B (3%), Cu (1%), Fe (7%), Mn (87%) e Zn (2%). Entre os três cenários de colheita avaliados, Ca e K foram os elementos que apresentaram o maior risco para a manutenção da produtividade.Palavras-chave: Manejo nutricional; Solos florestais; Sustentabilidade. BIOMASS AND NUTRIENTS OF Eucalyptus dunnii Maiden STAND IN PAMPA GAÚCHOABSTRACT -The study aimed to quantify biomass and nutrients as well as the effects on productivity and on site, according to the intensity of harvest in stand of Eucalyptus dunnii, with four years in Alegrete-RS. The inventory was conducted for the dendrometric characterization of the stand. The trees were compartmentalized in root, stem wood, stem bark, branches and leaves. Samples were collected and analyzed for the concentration of nutrients. The total tree biomass was 121.9 Mg ha -1, with the following distribution order of components: stem wood > root >branches> stem bark > leaves. In overall terms, for aboveground biomass, there was 985 kg ha -1 macronutrients and 32,5 kg ha -1 micronutrient, distributed: N ( 24%), P ( 2%) , K (23 %) , Ca ( 34%) , Mg (13% ) and S ( 4%) and B (3%) , Cu (1%), Fe ( 7%), Mn ( 87%) and Zn (2%). Among the three harvesting scenarios evaluated Ca and K were the elements that showed the greatest risk to the maintenance of productivity.

Atmospheric deposition is responsible for the ions input, which may be due to dust and aerosols and rainfall. During rainfall a portion is intercepted by the tree canopy and returned to the atmosphere by evapotranspiration, another part crosses the forest canopy called throughfall and stemflow. The objective of the study was to quantify incident rainfall partitioning into throughfall, stemflow and canopy interception in a Eucalyptus dunnii stand in southern Brazil. Four plots of 20 m × 21 m were demarcated. The rainfall consists 3 rain collectors in an open area. The throughfall consisted 3 collectors per plot in the line, interlining and diagonal positions of the trees. The stemflow consisted in the installation of three systems per plot formed by a hose in the trunk of the tree that leads the solution to a reservoir. The adjustment of the throughfall, stemflow and canopy interception in function of the incident precipitation was of 99%, 90% and 52%. As the volume of rainfall increases, the coefficient of variation decreases. The annual rainfall was 1903 mm, with a canopy interception average of 8.9%.

RESUMO O trabalho objetivou identificar os principais atributos químicos de solo que limitam o crescimento do

Resumo: Estudos relacionados à produção de biomassa e acúmulo de nutrientes são a base para a compreensão da dinâmica nutricional em povoamentos florestais. O objetivo do presente trabalho foi quantificar a biomassa e o estoque de nutrientes, em um povoamento de Eucalyptus dunnii, aos 60 meses de idade, estabelecido em Alegrete, Rio Grande do Sul. A amostragem da biomassa foi realizada a partir de doze árvores, que foram seccionadas ao nível do solo e a biomassa foi fracionada nos componentes: folhas, galhos, casca do tronco e madeira do tronco, com determinação de massa seca e tores de nutrientes. A biomassa total acima do solo foi de 58,76 Mg ha -1 , com sequência decrescente de alocação em madeira do tronco > casca do tronco > galhos > folhas. O estoque total de nutrientes foi de 175,5; 18,2; 171; 278,1; 69,1 e 21,5 kg ha -1 de N, P, K, Ca, Mg e S, respectivamente. Ressalta-se a importância da manutenção de resíduos da colheita sobre o solo, a fim de otimizar a ciclagem de nutrientes em função dos altos teores destes contidos nas folhas, casca e galhos.Palavras -chave: Nutrição florestal; Silvicultura; Ciclagem de nutrientes. Nutrients and biomass quantification in Eucalyptus dunnii Maiden stand established in Pampa biomeAbstract: Studies related to biomass production and accumulation of nutrients, are the basis for understanding the nutritional dynamics in forest stands. The objective of this study was to quantify the biomass and nutrient stocks, in a Eucalyptus dunnii stand, at 60 months old, established in Alegrete, Rio Grande do Sul. The sampling of biomass was taken from twelve trees which were cut at soil level and the fractional biomass components: leaf, branches, trunk bark and stem wood, with dry mass determination and nutrients concentration. The total above ground biomass was 58.76 Mg ha -1 , with decreasing sequence in the magnitude of the stem wood > trunk bark > branches > leaves. The total stock of nutrients was 175.5; 18.2; 171; 278.1; 69.1 and 21.5 kg ha -1 of N, P, K, Ca, Mg and S, respectively. We emphasize the importance of maintaining of harvest residues in the soil to optimize nutrient cycling due to high levels of these in the leaves, bark and branches.

-In a forest stand, litterfall is primarily responsible for the retention and return of nutrients to the soil. The objective of this study was to evaluate the return of nutrients through litterfall in a stand of Eucalyptus dunnii in a Pampa biome. For quantification of litterfall, four 420-m² installments were marked; within each one, four 0.50-m² collection plots were distributed. For the collection of thick branches, four 7.00-m² subplots were staked out. The collected litterfall was separated into leaf, twig, thick branch, and miscellany fractions for subsequent chemical analysis. The total litterfall measured was 6.99 Mg ha -1 yr -1 , and comprised 61.57% leaves, 17.34% twigs, 13.83% thick branches, and 7.26% miscellany. The total amount of macronutrients in the litterfall was 160.22 kg ha -1 yr -1 , and the macronutrient transfer order was the same for the leaf, twig, and thick branch fractions (Ca > N > K > Mg > S > P). The total quantity of micronutrients was 7.55 kg ha -1 yr -1 , and the transfer order was Mn > Fe > B > Zn > Cu. Maintaining litterfall on the site, especially in degraded or low fertility soils like in the Pampa biome, may contribute to possible improvements in soil characteristics.Keywords: Forest nutrition; Nutrient cycling; Pampa biome. DEVOLUÇÃO DE NUTRIENTES ATRAVÉS DA SERAPILHEIRA PRODUZIDA EM UM POVOAMENTO DE Eucalyptus dunnii Maiden EM SOLO ARENOSORESUMO -A produção de serapilheira é a principal responsável pela retenção e devolução de nutrientes para o solo em um povoamento florestal. O objetivo deste trabalho foi avaliar a devolução de nutrientes por meio da serapilheira produzida em um povoamento de Eucalyptus dunnii, no bioma Pampa. Para a quantificação da serapilheira produzida, foram demarcadas quatro parcelas de 420 m², e no interior de cada parcela foram distribuídos quatro coletores de 0,50 m². Para a coleta dos galhos grossos demarcou-se quatro sub-parcelas de 7,00 m 2 . O material coletado foi separado nas frações folhas, galhos grossos, galhos finos e miscelânea, com posterior análise química. A serapilheira produzida foi de 6,99 Mg ha -1 ano -1 , distribuída em 61,57%, 17,34%, 13,83% e 7,26%, nas folhas, galhos finos, galhos grossos e miscelânea, respectivamente. A quantidade de macronutrientes na serapilheira foi de 160,22 kg ha -1 ano -1 , sendo que, a ordem de transferência foi a mesma para as frações folhas, galhos finos e galhos grossos (Ca > N > K > Mg > S > P). Para os micronutrientes a quantidade foi 7,55 kg ha -1 ano -1 , seguindo a ordem decrescente de Mn > Fe > B > Zn > Cu. A manutenção da serapilheira no sítio, principalmente em solos degradados ou de baixa fertilidade natural, como é o caso da região do bioma Pampa, poderá contribuir com possíveis melhorias nas características do solo.Palavras-chave: Nutrição florestal; Ciclagem de nutrientes; Bioma Pampa.

Resumo: O presente estudo teve como objetivo estimar o estoque de biomassa e de nutrientes em um povoamento do híbrido de Eucalyptus urophylla x Eucalyptus grandis, aos 4,5 anos de idade, para isso, foram instaladas aleatoriamente quatro parcelas com dimensões de 21,0 m x 27,5 m. A partir da distribuição diamétrica do povoamento foram determinadas quatro classes de diâmetro e em cada classe foram amostradas três árvores (limite inferior, central e limite superior). Para estimar a biomassa das raízes a coleta foi realizada na área útil das árvores do limite central de cada classe. Após a amostragem e a identificação de cada componente da biomassa, estas foram encaminhadas para o laboratório, onde foram secas, pesadas, moídas e analisadas quimicamente. Os resultados encontrados a partir das análises foram: para a estimativa de biomassa total: 75 Mg ha -1 , com a seguinte proporção: madeira (61,2%), raiz (15,4%), galhos (10,2%), casca (7,7%) e folhas (5,5%). Salientase que a biomassa se encontra predominantemente alocada no fuste (68,9%). Cabe ressaltar que, em média, o acúmulo de nutrientes foi maior na madeira, seguido pelas folhas, raízes, galhos e cascas, apresentando a seguinte magnitude: Ca > K > N > Mg > S > P, com a maior quantidade de Ca alocada no fuste. A partir disso, entende-se que o estoque de nutrientes na biomassa foi elevado em relação ao solo de baixa fertilidade natural.Palavras -chave: Ciclagem de nutrientes; Nutrição florestal; Matéria orgânica. Stock of biomass and nutrient in a stand of hybrid Eucalyptus urophylla x Eucalyptus grandis in Pampa Biome -RSAbstract: This study aimed to estimate the stock of biomass and nutrients in a hybrid stand of Eucalyptus urophylla x Eucalyptus grandis, with 4.5 years old. In order to estimate the biomass, four plots with dimensions of 21.0 m x 27.5 m were randomly allocated. From the diameter distribution of the stand were determined four diameter classes and in each class were sampled three trees (lower, middle and top limits). To estimate the roots biomass, the collection was held in the useful area of the trees of the central limit of each class. After sampling and identification of each biomass component, they were sent to the laboratory where they were dried, weighed, ground and carried the chemical analysis. The estimated total biomass was 75 Mg ha -1 with the following proportions: wood (61.2%), root (15.4%), branches (10.2%), bark (7.7%) and leaves (5.5%). The biomass is predominantly allocated to the stem (68.9%). On average, the accumulation of nutrients was higher in the wood, followed by the leaves, roots, branches and bark. The accumulation of nutrients presented the following scale: Ca > K > N > Mg > S > P, with the higher amount of Ca allocated to the stem. The stock of nutrients in the biomass was high in relation to the low fertility soil.

Atmospheric deposition is responsible for the ions input, which may be due to dust and aerosols and rainfall. During rainfall a portion is intercepted by the tree canopy and returned to the atmosphere by evapotranspiration, another part crosses the forest canopy called throughfall and stemflow. The objective of the present work was to quantify the nutrient input of the incident rainfall, throughfall, stemflow and canopy enrichment in an Eucalyptus dunnii plantation, established in soil with low natural fertility. Four plots of 20 m × 21 m were demarcated. The rainfall consists 3 rain collectors in an open área. The throughfall consisted 3 collectors per plot in the line, interlining and diagonal positions of the trees. The stemflow consisted in the installation of three systems per plot formed by a hose in the trunk of the tree that leads the solution to a reservoir. Through rainfall, 29.5 kg ha-1 of nutrients were supplied. When we consider the sum of the throughfall and stemflow, the amount of nutrients was 77.6 kg ha-1. After interaction with the tree canopy 48.2 kg ha-1 of nutrients were incorporated. Potassium showed the highest enrichment: 607%. The average nutrient enrichment was 163%. The input of N and K via incident rainfall was 1.8 and 3.1 kg ha-1. Considering the fertilization described in the methodology, this contributed amount represents 6.1 and 2.6% of the total. If we consider the rotation of 7 years for Eucalyptus dunnii, the contribution at the end of rotation represents 42.4 and 18% of N and K2O. The interaction with the canopy of Eucalyptus dunnii enriches the rainwater with nutrients making the solution with a more basic character.

The evaluation of litterfall and nutrient return is important for understanding the dynamics of nutrient cycling. Although required in smaller quantities by plants, micronutrients have unique importance in biogeochemical regulation. The objective of the present study was to quantify the litterfall and the concentration of micronutrients in the different fractions and seasons of the year in Eucalyptus dunnii stand. Four plots of 20 m x 21 m were demarcated. The collection of leaf litter, twigs (diameter <0.5 cm) and miscellaneous resulted in the installation of 4 collectors with an area of 0.5 m² in each plot. For the quantification of the thick branches fraction (diameter> 0.5 cm), four useful areas of medium-diameter trees were demarcated in each plot. The leaf fraction represented 59% of litterfall and the transfer order was Mn> Fe> B> Zn> Cu, totaling 8.04 kg ha-1. The leaf fraction presented the highest concentrations for B and Mn. The litterfall was seasonal with summer and spring differing statistically from winter and the temperature variable explains the deposition pattern of the same.