ABSTRACT Productivity in clonal eucalyptus plantations depends on the genetic material and on the demand and cycling of nutrients, making studies that evaluate these requirements necessary. The aim of this study was to evaluate the effect of management (with and without thinning) on the deposition, chemical composition and nutrient contribution in litter at different clonal or stallion eucalyptus plantations. The experiment was conducted under a subdivided plot design for comparison of “clone” and “thinning” treatments. Plots were composed of eight different clonal and eucalyptus seed plantations, with subplots being areas where thinning was performed and areas without thinning. Litter deposition pattern associated to seasons was observed, with higher values in the spring and summer. The leaf fraction was more representative in relation to nutrients. Deposition values were close in most plantations. Nutritional contents were higher in leaves of areas with thinning in relation to the other areas.

RESUMO A biomassa residual agrícola é uma importante fonte de energia e sua produção e qualidade varia com o manejo das lavouras. O objetivo deste estudo foi avaliar o efeito da distribuição de plantas e da adubação nitrogenada sobre o potencial de produção de energia da biomassa do milho cultivado sob sistema de plantio direto. O experimento de campo foi instalado no sudeste do Brasil, com cinco doses de nitrogênio (0, 60, 120, 180 e 240 kg ha-1) e dois espaçamentos entrelinhas (0,4 e 0,8 m). Foram realizadas avaliações de produtividade de grãos, produtividade de biomassa residual e potencial de bioenergia em diferentes partes da planta (grão, colmo + folha, palha da espiga e sabugo). A variação no espaçamento não alterou o rendimento de grãos. A produtividade de folhas + palha de espiga foi maior em 0,8 m do que 0,4 m de espaçamento. A aplicação de nitrogênio resultou no aumento do rendimento de grãos e da produtividade de biomassa. O nitrogênio influência o potencial da bioenergia ao aumentar a biomassa e o poder calorífico. Com a dose de 226 kg ha-1 de nitrogênio, taxa máxima para o rendimento de grãos, e considerando apenas o uso de palha da espiga e sabugo, é possível gerar 2712 kWh ha-1 de bioenergia.

ABSTRACT Agricultural residual biomass is an important source of energy, and its production and quality vary according to the crop management. This study aimed to assess the effects of plant distribution and nitrogen fertilization on the energy production potential of the biomass of maize cultivated under no tillage. The field experiment was installed in southeast Brazil using five nitrogen rates (0, 60, 120, 180, and 240 kg ha-1) and two inter-row spacings (0.4 and 0.8 m). Grain yield, residual biomass productivity, and bioenergy potential in different parts of the plant (grain, stalk+leaf, husk, and cob) were assessed. No change in grain yield was observed using narrow row spacing. Stalk+leaf and husk productivity was higher using 0.8 m than using 0.4 m of inter-row spacing. Nitrogen application resulted in increased grain yield and biomass productivity. Nitrogen influences the bioenergy potential by increasing the biomass and calorific value. Application of the maximum nitrogen fertilization rate is recommended for grain yield considering the use of only the husk and cob can generate 2712 kWh ha-1 of bioenergy.

ABSTRACT We assessed litterfall and nutrient cycling in an old-growth Atlantic rainforest in southern Brazil. Plant litter collected monthly was separated into: leaves, twigs, reproductive organs, and fragments, and dried, weighed, and ground. Determination of carbon, nitrogen, phosphorus, potassium, calcium, magnesium, and sodium contents of different litter fractions was also performed. The total deposition was 8.44 Mg-1 ha-1 year-1, with a higher proportion of leaves fraction. Litterfall predominated in spring and summer, coinciding with the highest average temperature and rainfall in the study area. For leaves, twigs and fragments, the elements sequence of concentration was C>N>Ca>K>Mg>P>Na; whereas for reproductive organs it was C>N>K>Ca>Mg>P>Na. A higher concentration of nutrients was observed in spring and summer for the leaves fraction. The quantitative transfer of nutrients by litterfall fractions to the forest soil followed the same sequence observed for the concentration of nutrients.