Direct seeding is a promising method for reducing restoration costs, but methodological adjustments are still needed to reduce the uncertainties to achieve a desired seedling density in the field. Here, we investigated the technical approaches and outcomes of direct seeding of fast-growing native trees for cost-effective restoration of the Brazilian Atlantic Forest. Sixteen tree species were manually sown at three seeding densities in planting lines prepared with a subsoiler, in two experimental areas, which were weeded with hoes and had leaf-cutter ants controlled with insecticide baits. Seedling density was monitored for 30, 90, and 180 days after sowing. No substantial change in tree density was observed 30 days after sowing, thus allowing fast corrective actions to adjust tree density. Only a minor proportion of the sown viable seeds resulted in established seedlings at 180 days (4-12% for the community; approximately 25% for the species with the best performance). However, tree density was high (6,000 on average; approximately 1,400-13,000 trees/ha) and allowed an effective canopy development. Overall, seedling density was linearly and positively associated with seeding density, was highly influenced by the species used, and was higher in the soil with higher sum of bases. Buying seeds would be, for most species, less costly than buying nursery-grown seedlings for achieving the expected tree densities in the field. These results evidence the potential of direct seeding for reducing restoration costs, as well as the need to select species with better performance and adjust seeding densities to optimize the use of this method. Implications for Practice• Direct seeding of fast-growing native trees is a cost-effective approach for a rapid recovery of a forest canopy in restoration sites. • Direct seeding of fast-growing native trees shows better establishment in soils with higher sum of bases, so seeding densities can be lower. • Plant functional traits as seed size and association with nitrogen-fixing bacteria may improve tree species establishment in direct seeding. • Direct seeding of species with rapid germination allows anticipating corrective actions resulted from failures in seedling densities; hence, direct seeding can be used as a first try to recover native forest cover at low costs.

The objectives of the study were to assess changes in fine root anisotropy and specific root lengths throughout the development of Eucalyptus grandis (W. Hill ex Maiden) plantations and to establish a predictive model of root length density (RLD) from root intercept counts on trench walls. Fine root densities (<1 mm in diameter) were studied in 6-, 12-, 22-, 28-, 54-, 68-and 72-month-old E. grandis plantations established on deep Ferralsols in southern Brazil. Fine root intercepts were counted on 3 faces of 90-198 soil cubes (1 dm 3 in volume) in each stand and fine root lengths (L) were measured inside 576 soil cubes, sampled between the depths of 10 cm and 290 cm. The number of fine root intercepts was counted on one vertical face perpendicular to the planting row (N t ), one vertical face parallel to the planting row (N l ) and one horizontal face (N h ), for each soil cube sampled. An overall isotropy of fine roots was shown by paired Student's t-tests between the numbers of fine roots intersecting each face of soil cubes at most stand ages and soil depths. Specific root lengths decreased with stand age in the upper soil layers and tended to increase Plant Soil (2010) 334:261-275 in deep soil layers at the end of the rotation. A linear regression established between N t and L for all the soil cubes sampled accounted for 36% of the variability of L. Such a regression computed for mean N t and L values at each sampling depth and stand age explained only 55% of the variability, as a result of large differences in the relationship between L and N t depending on stand productivity. The equation RLD= 1.89*LAI*N t , where LAI was the stand leaf area index (m 2 m −2 ) and N t was expressed as the number of root intercepts per cm 2 , made it possible to predict accurately (R 2 =0.84) and without bias the mean RLDs (cm cm −3 ) per depth in each stand, for the whole data set of 576 soil cubes sampled between 2 years of age and the end of the rotation.

RESUMO -O conhecimento das características do sistema radicular auxilia na definição de práticas de preparo de solo e fertilização. O objetivo deste trabalho foi estimar a biomassa, o conteúdo de nutrientes em raízes, o comprimento e a área de raízes finas e médias e a eficiência de utilização de macronutrientes da teca (Tectona grandis) para formação de área radicular em diferentes profundidades do solo. A separação das raízes do solo foi feita estratificando-as em grossas (>5 mm), médias (2 a 5 mm) e finas (< 2 mm), para determinação de N, P, K, Ca, Mg e S. As raízes médias e finas (± 0,5 g) foram digitalizadas e quantificadas por intermédio do programa QuantRoot®, obtendo-se o diâmetro, a área e o comprimento. A biomassa total de raízes finas e médias foi de 1.335 e 1.258 kg ha -1 respectivamente, e 56,2% das raízes finas e 44,4% das raízes médias concentram-se nos primeiros 20 cm do solo. O comprimento total de raízes finas foi de 8.237 km ha -1 , com 57,4% nos primeiros 20 cm de profundidade. A superfície total de raízes finas foi de 18.441 m² ha -1 , com 57% dessa superfície nos primeiros 20 cm do solo. A quantidade total de nutrientes nas raízes, na camada de solo estudada (0-60 cm), em ordem decrescente, foi K > Ca > N > Mg > P > S. O fósforo e o enxofre são os nutrientes com maior eficiência de utilização para formação de área radicular em plantios de teca.Palavras-chave: Tectona grandis; Área radicular específica; Nutrição florestal. NUTRIENT USE EFFICIENCY FOR THE FORMATION OF FINE AND MEDIUM ROOTS IN TEAK STANDS

No abstract

Nutrients found in residues from agricultural cultures are important reserves for subsequent crops. The objective was to assess the decomposition and release of nutrients from different crop residues for subsequent soybean cultivation. The study was conducted in Mid-Northern Mato Grosso State, Brazil. The residual straw of cropping systems -maize, brachiaria and maize/brachiaria consortium -were sampled, weighted, disposed in litter bags and then distributed on the soil. The adopted experimental design followed the completely randomized arrangement with three repetitions. Treatments were determined based on harvest time, which was performed every 14 days within 140 days for maize, and within 154 days for brachiaria and for the consortium. The remaining dry matter and nutrients content, and half-time life were evaluated. Maize showed the highest straw dry matter yield (14,176 kg ha -1 ), and the consortium recorded the biggest nutrient accumulation per hectare (K=172.2; N= 141.7 and Ca=56.0 kg ha -1 ). Brachiaria straw presented the fastest decomposition rate (85%) and the highest nutrient release (K=99%; N=92%; Mg=98% and Ca=90% of total initial content). The total K released reached 150 kg ha -1 , which can fit the needs of soybean crops.Key words: crop management; integrated; mixed systems; nutrient cycling Decomposição e liberação de nutrientes de resíduos de culturas no sistema de cultivo soja-milho RESUMO: Os nutrientes contidos nos restos culturais representam uma importante reserva para culturas subsequentes. O objetivo foi avaliar a decomposição e a liberação de nutrientes de diferentes resíduos de culturas para subsequente cultivo da soja. O estudo foi realizado na região Médio Norte do estado de Mato Grosso, Brasil. A palhada residual dos sistemas de cultivo; milho, braquiária e consórcio milho/braquiária foram amostrados, pesados e acomodadas em litter bags e distribuídos sobre o solo. O design experimental foi o inteiramente casualizado com três repetições. Os tratamentos foram estabelecidos com base no tempo de colheita, realizado a cada 14 dias, em um período de 140 dias para o milho e 154 dias para a braquiária e consórcio, aonde foi avaliando a permanência da matéria seca e nutrientes e o tempo de meia vida. O milho apresentou a maior produtividade de matéria seca (14.176 kg ha -1 ), e o consórcio o maior acúmulo de nutrientes por hectare (K=172,1; N= 141,7 e Ca=56,0 kg ha -1 ). A braquiária apresentou a maior taxa de decomposição (85%) e a maior porcentagem de liberação de nutrientes (K=99%; N=92%; Mg=98% e Ca=90% do conteúdo inicial). A quantidade de K liberado pode ser de até 150 kg ha -1 o que pode corresponder às necessidades da soja.Palavras-chave: manejo de culturas; integrados; sistemas mistos; ciclagem de nutrientes Decomposition and release of nutrients from crop residues on soybean-maize cropping systems Rev. Bras.