NUTRIENT CYCLING IN EUCALYPTUS DUNNII: MICRONUTRIENTS IN THE LITTERFALL

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), 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

Estoque de biomassa e de nutrientes em um povoamento do híbrido Eucalyptus urophylla x Eucalyptus grandis no Bioma Pampa – RS

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.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%). Salienta-se 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

Limitações químicas ao crescimento inicial de Eucalyptus saligna em solos arenosos do Pampa Gaúcho: estudo de caso

O trabalho objetivou identificar os principais atributos químicos de solo que limitam o crescimento do Eucalyptus saligna em plantios sem calagem na região Sudoeste do Rio Grande do Sul, bem como determinar os valores críticos de cada fator. O estudo foi realizado em povoamentos florestais de dois Latossolos Vermelhos e um Neossolo Quartzarênico da região. Foram realizadas análises químicas do solo e, através de correlações (P<0,05) entre estes e variáveis de crescimento das plantas, verificou-se que os atributos que mais limitaram o crescimento das plantas foram a saturação por Al, a saturação por bases e o teor de Mg trocável, com decréscimo de até 50% nos parâmetros de crescimento. As correlações com os atributos químicos da camada subsuperficial de solo (20-40cm) foram mais significativas do que na camada superficial (0-20cm). Os níveis críticos médios para obtenção de 80% do rendimento relativo no crescimento em diâmetro e em volume de plantas foram de 79% para saturação por Al, 8,3% para saturação por bases e 0,3 cmolc dm-3 para o teor de Mg trocável. Os resultados indicam que a calagem não deve ser suprimida dos plantios de eucalipto em solos ácidos do Pampa gaúcho, mas a quantidade necessária de calagem para esta cultura parece ser menor do que a atualmente recomendada

NUTRIENT RETURN THROUGH LITTERFALL IN A Eucalyptus dunnii Maiden STAND IN SANDY SOIL

ABSTRACT 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 sub-plots 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

MICRONUTRIENTS AND BIOMASS IN Eucalyptus dunnii Maiden STAND

<div><p>ABSTRACT The expansion of silviculture in Brazil, and the consequent intensive practices for soil preparation with high demand for fertilizers require sustainable nutrient management of forest sites. The objective of this study was to quantify the biomass and the micronutrient stocks of a 60-month-old Eucalyptus dunnii stand established in Alegrete, Rio Grande do Sul. The stand was established in a Rhodic Paleudult soil with low fertility and texture varying between sandy loam and sandy-clay loam. For the sampling of stand biomass, twelve trees were harvested, sectioned at ground level, and subsequently fractionated into the components roots, leaves, branches, stembark and stemwood to determine the dry mass and micronutrient content. The total biomass of the stand was 67.49 Mg ha-1, with mass allocation in descending order from: stem wood > root > bark > branches > leaves. Total micronutrient stocks for boron (B), copper (Cu), iron (Fe), manganese (Mn) and zinc (Zn) were 562.57, 401.46, 9913.28, 31877.82, and 766.96 g ha-1, respectively. In addition, we found greater accumulation of Zn in the wood, high Mn accumulation especially in the bark, and high Fe content in the roots. Therefore, based on these micronutrient levels and their allocation between biomass fractions, we emphasize that the practice of retaining forest residues on-site after harvest is essential for forest nutrition through nutrient cycling and for soil conservation and fertility.</p></div

Weed Coexistence in Eucalyptus Hybrid Stands Decreases Biomass and Nutritional Efficiency Mid-Rotation

Determining the period of weed coexistence with eucalyptus stands assists in the integrated management of weed competition, which reduces the application of herbicides, economic costs, and environmental damage. Therefore, the objectives of the present study were to evaluate the impact of a hybrid stand of Eucalyptus grandis × Eucalyptus urophylla trees on biomass production, the concentration and stock of macro and micronutrients, and the efficiency of nutrient utilization under different periods of coexistence with weeds. Our study is the first to report the impacts of weed management on the biomass and nutrients present in the leaves, branches, stembark, and stemwood at the time of mid-rotation (4.5 years old). The experiment was carried out in southern Brazil in the Pampa biome and followed a randomized block design, with three replications. The treatments consisted of increasing periods of coexistence with or control of weeds. The total biomass in the coexistence up to 378 days treatment was 53.7 Mg ha−1, and in the control treatment up to 168 days, it was 81.4 Mg ha−1, differing statistically. This reduction was in the order of 34%. The continuous presence of weeds led to a significant reduction in the production of wood and total biomass. The highest nutrient utilization efficiency (NUE) was observed for wood. The control of weeds for up to 168 days promoted greater productivity than controlling weeds for 378 days. This recommendation can be adopted by plantation managers for this region, reducing the amount of herbicide applied on the stand