The main challenges faced in the reclamation of severely degraded lands are in the management of the systems and finding plant species that will grow under the harsh conditions common in degraded soils. This is especially important in extremely adverse situations found in some substrates from mining activities or soils that have lost their upper horizons. Under these conditions, recolonization of the area by native vegetation through natural succession processes may be extremely limited. Once the main physical and chemical factors restrictive to plant growth are corrected or attenuated, the introduction of leguminous trees able to form symbioses with nodulating N₂-fixing bacteria and arbuscular mycorrhizal fungi constitutes an efficient strategy to accelerate soil reclamation and initiate natural succession. These symbioses give the legume species a superior capacity to grow quickly in poor substrates and to withstand the harsh conditions presented in degraded soils. In this article we describe several successful results in Brazil using N₂-fixing legume tree species for reclamation of areas degraded by soil erosion, construction and mining activities, emphasizing the potential of the technique to recover soil organic matter levels and restore ecosystem biodiversity and other environmental functions.

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Since the 1970s the area under sugarcane in Brazil has increased from 2 million to over 5 million ha (M ha), and it is expected to pass the 7 M ha mark in 2007. More than half of the cane is harvested to produce bioethanol as a fuel for light vehicles. The distilleries produce approximately 13 L of distillery waste (vinasse) for each litre of ethanol produced. In the 1980s there was considerable concern over the long-term effects of the disposal of this material (containing about 1% carbon and high in K) on cane yields if it was applied to the field. At the same time there was a growing movement to abandon the practice of pre-harvest burning and some research was showing that some Brazilian varieties of sugar cane were able to obtain significant contributions of N from plant-associated biological nitrogen fixation (BNF). For these reasons an experiment was installed on a cane plantation in the state of Pernambuco, NE Brazil to investigate the long-term effects of vinasse and N fertiliser additions and the practice of pre-harvest burning on crop and sugar yield, soil fertility parameters, N balance and soil C stocks. The results showed that over a 16-year period, trash conservation (abandonment of burning) increased cane yields by 25% from a mean of 46 to 58 Mg ha )1 . Vinasse applications (80 m 3 ha )1 crop )1 ) increased mean cane and sugar yield by 12 to 13% and the application of 80 kg N ha )1 as urea increased cane yields by 9%, but total sugar yield by less than 6% (from 7.0 to 7.4 Mg ha )1 crop )1 ). The total N balance for the soil/plant system when only the surface 20 cm of the soil was considered was positive in plots where no N fertiliser was added. However, the data indicated that during the 16 years of the study considerable quantities of soil organic matter were accumulated below 20 cm depth such that the N balance considering the soil to 60 cm depth was strongly positive, except where N fertiliser was added. The data indicated that there were considerable BNF inputs to the system, which was consistent with its low response to N fertiliser and low N fertiliser-use-efficiency. There were no significant effects of vinasse or urea addition, or trash conservation on soil C stocks, although the higher yields proportioned by trash conservation had potentially significant benefits for increased mitigation of CO 2 emissions where the main use of the cane was for bioethanol production.

This paper originates from an address at the 8th International Symposium on Nitrogen Fixation with Non-Legumes, Sydney, NSW, December 2000 The use of the 15N natural abundance technique to quantify contribution of biological nitrogen fixation (BNF) to any plant is based on the observation that N derived from soil is generally slightly different [usually higher in 15N abundance (δ15N‰)] than that of the air. Plants or micro-organisms growing solely on BNF generally accumulate N with 15N isotopic abundance lower than that of the air (i.e. δ15N‰ is negative), while plants obtaining all N from the soil generally show a positive δ15N‰ signal. The technique is applied by estimating the 15N abundance of the putative ‘N2-fixing’ crop and analysing the 15N abundance of neighbouring non-N2-fixing reference plants. However, often there are such large variations in the N derived from the soil by different non-N2-fixing plants that in natural ecosystems it is often impossible to even distinguish plants that are benefiting form BNF, let alone quantity this contribution. The reasons why soil derived N can vary so widely, especially in natural ecosystems, are briefly discussed and a sampling strategy is described to assess possible BNF inputs to sugar cane plants in commercial plantations in Brazil. The results suggest that in nine of the 11 sites studied, BNF inputs were significant ranging from 25 to 60% of N assimilated.

& Segundo Urquiaga (2) RESUMOAs práticas da queima, aplicação de vinhaça e fertilizante nitrogenado são comuns na cultura de cana-de-açúcar. No entanto, estudos de longa duração são pouco encontrados na literatura. Neste trabalho, realizado na Usina Cruangi, Timbaúba, PE, transição entre a Zona da Mata e o Agreste daquele Estado, objetivou-se avaliar o efeito da aplicação de N (80 kg ha -1 na forma de uréia), da vinhaça (80 m 3 ha -1 ) e da queima (com ou sem queima) da palhada antes do corte, entre 1983 e 1999, em características tecnológicas da cultura de cana-de-açúcar. O delineamento experimental foi o de blocos ao acaso, em esquema fatorial completo 2 x 2 x 2, e quatro repetições. O experimento teve duas fases: a primeira, de 1983-1992, e a segunda, de 1992-1999. A aplicação de N afetou as características tecnológicas da cana-de-açúcar; no entanto, o ganho de produtividade de colmos proporcionado por esta prática favoreceu a produção de açúcar e compensou tais efeitos. A aplicação de vinhaça e a manutenção da palhada no sistema não afetaram, de forma consistente, as características tecnológicas da cultura de cana-de-açúcar, embora tenham influenciado, de forma positiva, a produção de açúcar, de acordo com o ganho de produtividade.Termos de indexação: cana crua, açúcar, adubação.

-Information on the recovering of areas of gravel extraction of the Caatinga biome are scarce. Thus, the objective of this work was to assess the soil fauna as bioindicator of soil quality, evaluating areas with addition of topsoil (WAT) and control areas (CWT) without the addition of topsoil used for forest plantations, which were implemented for recovering gravel extraction areas. A native forest of the Caatinga biome (NFC) was taken as a reference. Ten traps with three replicates were installed in each area, which were evaluated in a randomized block design in split-plot arrangement at the end of the rainy season of different years, 0, 1, 3 and 6 years after the experiment implementation. A total of 45,740 specimens were captured. These specimens were from 36 taxonomic groups. The Acari, Diptera, Entomobryomorpha, Formicidae, Poduromorpha and Symphypleona were the predominant groups in all areas (WAT, CWT and NFC). Nine groups (25% of the total) had restricted occurrence. The fauna richness and diversity were higher in the NFC, followed by the WAT and CWT. The uniformity and total abundance of the soil fauna community showed no defined patterns. The abundance of most groups was inhibited in the treatments evaluated, compared with NFC, however, this adverse effect was more significant in CWT compared with WAT. The CWT and WAT had high similarity and both had very low similarity with NFC. The ecological complexity of soil fauna community was higher in NFC. The soil fauna was efficient as a bioindicator of soil quality, which was higher in WAT, compared with CWT. Keywords:Topsoil. Environmental indicators. Soil organisms. Gravel. Revegetation. FAUNA EDÁFICA COMO BIOINDICADORA DA RECUPERAÇÃO DE ÁREAS DEGRADADAS NOBIOMA CAATINGA RESUMO -Atualmente, há poucas informações sobre a recuperação de áreas onde ocorre a extração de piçarra na Caatinga. Objetivou-se avaliar o emprego da fauna edáfica como bioindicadora da qualidade do solo em áreas com e sem a adição de topsoil (CT e ST, respectivamente), em plantios florestais para a recuperação de áreas de extração deste recurso mineral. Considerou-se a mata nativa de Caatinga (MT) como referencial. Foram instaladas 10 armadilhas em três réplicas para cada tratamento, em delineamento em blocos casualizados em esquema de parcelas subdivididas, no final da estação chuvosa,em diferentes épocas (0, 1, 3 e 6 anos depois). Capturou-se um total de 45.740 organismos, distribuídos em 36 grupos taxonômicos, com o predomínio de Acari, Diptera, Entomobryomorpha, Formicidae, Poduromorpha e Symphypleona, em todos os tratamentos (ST, CT, MT). Nove grupos (25% do total) apresentaram ocorrência restrita. Os valores de riqueza e diversidade foram maiores na MT, seguidos do CT e ST. Não houve um padrão definido para a uniformidade e abundância total da comunidade. A maioria dos grupos apresentou inibição na abundância nos tratamentos testados em relação à MT, mas este efeito negativo foi relevante no ST, em comparação com o CT. A similaridade entre ST e CT foi elevada, e muito bai...

RESUMOOs Sistemas Agroflorestais (SAFs) trazem benefícios múltiplos e constituem uma alternativa para minimizar a degradação ambiental e alcançar um desenvolvimento sustentável, devido à diversidade de espécies que os compõe. O presente estudo avaliou a contribuição das leguminosas arbóreas, Gliricidia sepium e Acacia angustissima, cultivadas em aleias intercaladas com banana (Musa sp.) e açaí (Euterpe oleraceae), na implantação de Sistema Agroflorestal. Comparou-se a produção de biomassa e ciclagem de nutrientes no SAF, com a leguminosa herbácea Pueraria phaseoloides e adubação nitrogenada. O SAF foi implantado em maio de 2004, no Campo Experimental da Embrapa Agrobiologia, em Seropédica -RJ. O delineamento experimental foi de blocos casualizados com cinco tratamentos, constituídos das leguminosas acácia-angustíssima (Acacia angustissima), kudzu-tropical (Pueraria phaseoloides), gliricídia (Gliricidia sepium) dispostas nas entrelinhas da banana e do açaí; além de adubação nitrogenada com ureia, e cobertura viva oriunda da vegetação espontânea. Para quantificar a produção de biomassa e liberação de N, P, Ca, Mg e K in situ foram cortadas as leguminosas e roçado o kudzu-tropical e a vegetação espontânea. As determinações da matéria seca remanescente, liberação de nutrientes, constantes de decomposição e os tempos de meia-vida dos resíduos vegetais foram realizadas acondicionando-se 50 g de material fresco em litterbags, dispostos na superfície do solo, tomando-se amostras aos 0, 5, 10, 15, 20, 25, 30, 40, 60 e 75 após o início do experimento. Acacia angustissima e kudzu-tropical apresentaram maior produção de biomassa seca, igual a 10,8 Mg ha -1 . Os resíduos da gliricídia resultaram em maiores constantes de decomposição, nas duas estações do ano. Palavras-chave: cultivo em aleias; adubação verde; Musa sp. ABSTRACTThe Agroforestry Systems (SAFs) bring multiple benefits and they are an alternative to minimize environmental degradation, and to achieve a sustainable development, due to greatest diversity of species. This study evaluated the contribution of the leguminous trees, gliricídia sepium and Acacia angustissima, grown in alley cropping of banana (Musa sp.) and "açaí" palm (Euterpe oleraceae) used as green manure in the implantation of an Agroforestry Systems. They were compared the production of biomass, nutrients cycling, nitrogen intake, activity and diversity of soil fauna, and banana productivity in the SAF, and with