Summary 1.Little is known about the role of deep roots in the nutrition of forest trees and their ability to provide a safety-net service taking up nutrients leached from the topsoil. 2. To address this issue, we studied the potential uptake of N, K and Ca by Eucalyptus grandis trees (6 years of age -25 m mean height), in Brazil, as a function of soil depth, texture and water content. We injected NO ) tracers simultaneously in a solution through plastic tubes at 10, 50, 150 and 300 cm in depth in a sandy and a clayey Ferralsol soil. A complete randomized design was set up with three replicates of paired trees per injection depth and soil type. Recently expanded leaves were sampled at various times after tracer injection in the summer, and the experiment was repeated in the winter. Soil water contents were continuously monitored at the different depths in the two soils. 3. Determination of foliar Rb and Sr concentrations and 15 N atom % made it possible to estimate the relative uptake potential (RUP) of tracer injections from the four soil depths and the specific RUP (SRUP), defined as RUP, per unit of fine root length density in the corresponding soil layer. 4. The highest tracer uptake rates were found in the topsoil, but contrasting RUP distributions were observed for the three tracers. Whilst the RUP was higher for NO À 3 -15 N than for Rb + and Sr 2+ in the upper 50 cm of soil, the highest SRUP values for Sr 2+ and Rb + were found at a depth of 300 cm in the sandy soil, as well as in the clayey soil when gravitational solutions reached that depth. 5. Our results suggest that the fine roots of E. grandis trees exhibit contrasting potential uptake rates with depth depending on the nutrient. This functional specialization of roots might contribute to the high growth rates of E. grandis trees, efficiently providing the large amounts of nutrients required throughout the development of these fast-growing plantations.

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ABSTRACT:Sewage sludge (SS) has been widely used as organic fertilizer. However, its continuous use can cause imbalances in soil fertility as well as soil-water-plant system contamination.The study aimed to evaluate possible improvements in the chemical and microbiological characteristics of domestic SS, with low heavy metal contents and pathogens, through the composting process. Two composting piles were set up, based on an initial C/N ratio of 30:1, with successive layers of tree pruning waste and SS. The aeration of piles was performed by mechanical turnover when the temperature rose above 65 ºC. The piles were irrigated when the water content was less than 50 %. Composting was conducted for 120 days. Temperature, moisture content, pH, electrical conductivity (EC), carbon and nitrogen contents, and fecal coliforms were monitored during the composting. A reduction of 58 % in the EC of the compost (SSC) compared with SS was observed and the pH reduced from 7.8 to 6.6. There was an increase in the value of cation exchange capacity/carbon content (CEC/C) and carbon content. .In SSC, helminth eggs were eliminated, making application sustainable for agriculture purposes.

In soils of tropical climate regions the high acidity and the presence of exchangeable aluminum (Al3+), associated to low fertility, are the main restrainting factors for agricultural production. A laboratory experiment was conducted using 26 soils of different Brazilian regions, to investigate soil acidity components, giving emphasis to Al and their relations with chemical properties. The pH correlated positively with P, Ca, Mg, K, BS, CEC and V% values, and negatively with Al saturation. The Al3+ was the predominant exchangeable cation in 32% of the soils with pH below 5.6. The KCl titratable H+ represents the hydroxi-Al(OH)x complex with low stability and the Wolf-Morgan extracted Al corresponds to the exchangeable + non-exchangeable Al species. The Al3+ and low stability hydroxi-Al decreased quickly with increasing pH up to 5.5. The non-exchangeable Al increased up to pH 4.5, then decreased to pH 5.5 and had a small increment from 7.0 to 7.5.

The zinc (Zn) supply increases the fruit yield of Citrus trees that are grown, especially in the highly weathered soils of the tropics due to the inherently low nutrient availability in the soil solution. Leaf sprays containing micronutrients are commonly applied to orchards, even though the nutrient supply via soil could be of practical value. This study aimed to evaluate the effect of Zn fertilizers that are applied to the soil surface on absorption and partitioning of the nutrient by citrus trees. A greenhouse experiment was conducted with one-year-old sweet orange trees. The plants were grown in soils with different textures (18.1 or 64.4% clay) that received 1.8 g Zn per plant, in the form of either ZnO or ZnSO4 enriched with the stable isotope 68Zn. Zinc fertilization increased the availability of the nutrient in the soil and the content in the orange trees. Greater responses were obtained when ZnSO4 was applied to the sandy loam soil due to its lower specific metal adsorption compared to that of the clay soil. The trunk and branches accumulated the most fertilizer-derived Zn (Zndff) and thus represent the major reserve organ for this nutrient in the plant. The trees recovered up to 4% of the applied Zndff. Despite this relative low recovery, the Zn requirement of the trees was met with the selected treatment based on the total leaf nutrient content and increased Cu/Zn-SOD activity in the leaves. We conclude that the efficiency of Zn fertilizers depends on the fertilizer source and the soil texture, which must be taken into account by guidelines for fruit crop fertilization via soil, in substitution or complementation of traditional foliar sprays.

SUMMARYThe use of sewage sludge in Brazilian agriculture was regulated by the resolution no. 375 Conama, in 2006. However, there is a lack of research to adequate the mineral N and P fertilizer doses to be applied in agricultural fields treated with this residue. In a field experiment, the effects of application rates of sewage sludge and mineral N and P fertilizers on the productivity and technical characteristics of the cane-plant and first ratoon (residual effect) crops were evaluated. Four doses of sewage sludge (0, 3.6, 7.2 and 10.8 t ha -1 , dry base), of N (0, 30, 60 and 90 kg ha -1 ) and of P 2 O 5 (0, 60, 120 and 180 kg ha -1 ) were combined in a factorial and laid out on randomized block design, a with two replications. To evaluate the residual effect of the sludge, 120 kg ha -1 N and 140 kg ha -1 of K 2 O were applied in all plots. Sludge application at cane planting, with or without N and/or P fertilizer increased the stalk yield from 84 up to 118 t ha -1 , with no alteration in the sugarcane quality, compared with the application of NPK fertilizer alone, resulting in a stalk yield of 91 t ha -1 . The study of the response surface for stalk yield on lowfertility soil was the basis for a recommendation of mineral N and P fertilizer doses for sugarcane implantation as related to sewage sludge application rates. It was also concluded that a sludge application of 10.8 t ha -1 , which is the sludge dose established based on the N criterion according to the resolution Conama n o 375, could a) reduce the use of mineral N by 100 % and of P 2 O 5 by 30 %, with increments of 22 % in stalk yield, as a direct effect of sludge application to cane plant crop, and b) increase the stalk yield in the second harvest (first ratoon) by up (1)

Alterações em atributos químicos 529Alterações em atributos químicos de um Latossolo pela aplicação de composto de lixo urbano (1) Fernando Carvalho Oliveira (2) , Maria Emilia Mattiazzo, Claudio Roberto Marciano (4) e Cassio Hamilton Abreu Junior . Todas as propriedades químicas do solo estudadas aumentaram com as doses do composto, em ambos os anos agrícolas. Os incrementos observados nesses atributos, da primeira para a segunda aplicação, foram significativos, exceto a condutividade elétrica, que, embora tenha aumentado logo após a aplicação do resíduo, não atingiu níveis críticos e teve seus valores reduzidos com o tempo. Acúmulos nos teores de C orgânico do solo foram diretamente proporcionais às doses de aplicação. O aumento da CTC do solo foi conseqüência direta dos incrementos nos teores de C orgânico e nos valores de pH.Termos para indexação: carbono, compostos orgânicos, condutividade elétrica, pH, capacidade de troca de cátions, solo.Changes on some chemical attributes of a soil due to the application of solid urban waste compost Abstract A field experiment was conducted, during the years of 1996/97 and 1997/98, to evaluate the effects of the successive application of solid urban waste compost on organic carbon, electrical conductivity, pH, and cation exchange capacity (CEC) at field pH in a Typic Hapludox cropped with sugarcane. In the first year, besides lime + mineral fertilizer and control treatments, the compost was applied at a rate of 0, 20, 40, and 60 Mg ha -1 (dry basis). In the second year, the compost was reapplied at a rate of 24, 48, and 72 Mg ha . All studied soil properties increased with rate of compost application in both years. Attributes increments from the first to the second application were significant, except for electrical conductivity, which increased soon after the residue application, but did not reach critical levels and decreased along the time. Accumulation of organic C in soil was direct proportional to compost application rate. The increase of soil CEC was a consequence of the increments on organic C content and pH value.Index terms: carbon, organic compounds, electrical conductivity, pH, cation exchange capacity, soil.(1) Aceito para publicação em 4 IntroduçãoO potencial agronômico do composto de lixo urbano está fundamentado basicamente na elevada concentração de carbono orgânico presente em sua composição. Aumentar o teor de carbono orgânico de um solo pode significar melhorias nas suas propriedades físicas, químicas e biológicas. Além disso, esse resíduo encerra em sua composição apreciáveis quantidades de nutrientes, especialmente N, K e Ca (Xin et al., 1992;Abreu Junior et al., 2000).A possibilidade desse resíduo de incrementar os teores de carbono orgânico do solo foi verificada em estudos realizados em regiões sob clima temperado. Pesq. agropec. bras., Brasília, v. 37, n. 4, p. 529-538, abr. 2002 F. C. Oliveira et al. 530 Hortenstine & Rothwell (1972) verificaram aumentos de 41 e 169% nos teores de C orgânico de um solo degradado por mineração, 24 ...