E. F. C. Campello

Nitrogen-fixing legume tree species for the reclamation of severely degraded lands in Brazil.

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.

Sucessão vegetal em uma encosta reflorestada com leguminosas arbóreas em Angra dos Reis, RJ

n The floristic composition and natural regeneration under a 7-year-old legume tree plantation (Acacia auriculiformis, A. mangium e Mimosa tenuiflora) was investigated in comparing with a secondary forest 200 m away at Angra dos Reis, RJ. The hillside was divided in 3 parts following the slope. The lower part of the hillside was the nearest to the natural forest remnant. In 12 plots with 200 m 2 each, 4 of them in each section of the hillside, 699 plants larger then 40 cm height were observed, distributed in 25 families and 50 species. The families with the most individuals were Meliaceae (298), Euphorbiaceae (70), Piperaceae (64) and Lauraceae (41). The families with the most species were Solanaceae (7), Melastomataceae (5) and Myrtaceae (5). None of the legume species introduced in the area had produced natural regeneration. The evolution of natural succession acurred with a gradient in function of the slope and distance of the remnant natural forest. The higher density of individuals and species richness were found in the lowest part of the hillside.

Evaluation of the throughfall and stemflow nutrient contents in mixed and pure plantations of Acacia mangium, Pseudosamenea guachapele and Eucalyptus grandis

A interceptacao da chuva pela copa das florestas tem grande relevância no ciclo biogeoquimico de nutrientes nos solos de baixa fertilidade sob florestas nativas e plantadas. Entretanto, pouco se sabe sobre as modificacoes na qualidade dessa agua e no balanco hidrologico apos a interceptacao pela copa do eucalipto sob condicoes de plantios puros e mistos com leguminosas, no Brasil. Amostras de agua de chuva (RF), de precipitacao interna (TF) e de escoamento pelo tronco (SF), foram coletadas e analisadas quimicamente em plantios puros de mangium (especie fixadora de nitrogenio atmosferico - EFN), guachapele (EFN) e eucalipto (especie nao fixadora de nitrogenio - ENFN) e consorciados com guachapele e eucalipto, em Seropedica, Rio de Janeiro. Nove coletores de escoamento pelo tronco (colocados em arvores), nove pluviometros posicionados ao acaso nos plantios e tres fora da influencia deles foram utilizados no monitoramento durante 5,5 meses. A mangium direcionou 33,4% do total precipitado para o seu tronco. Uma estimativa baseada na correcao da media anual precipitada na area (1.213 mm) indicou uma contribuicao no aporte de nutrientes (kg ha-1) de 8,42; 0,95; 19,04; 6,74; 4,72; e 8,71 kg ha-1 dos elementos N-NH4+, P, K+, Ca+2, Mg+2 and Na+, respectivamente. A precipitacao interna participou com a maior parte da contribuicao, em comparacao com o escoamento pelo tronco. Os maiores aportes de N-NH4+ (15,03 kg ha-1) e K+ (179,43 kg ha-1) foram observados sob as copas de guachapele em plantio puro. Elevada quantidade de Na+ denota influencia do mar proximo a area experimental. A mangium foi a especie adaptada a competicao por agua. Comparativamente ao plantio puro de eucalipto, o plantio misto intensificou a lixiviacao de N, Ca e Mg da copa, enquanto o de K e o P aportaram em menores quantidades nesse plantio.

Características do solo na restauração de áreas degradadas na Reserva Biológica de Poço das Antas, RJ.

A project to restore a degraded area must firstly reestablish organic soil matter and nutrient cycling process. In order to evaluate the influence of indigenous tree plantations on changings in soil fertility and organic matter dynamics, an experiment was installed at the Poco das Antas Biological Reserve, an Atlantic Rain Forest remnant of ca. 5,200. Six treatments involved mature forests (F), 8-year-old mixed plantations of indigenous tree species (P), and abandoned pastures (G), at both the flooding (V) and the sloping (M) areas of the Reserve. The experimental design was completely randomized. Soil samples were collected at the layers 0-2.5cm; 2-5-7.5cm; and 7.5-20cm to evaluate soil pH, and Al, Ca+Mg, P, K, C and N contents. The PV treatment showed higher values for the exchangeable cations, C and soil organic matter (SOM) contents, indicating high cycling rates and biological activity. Soil stability was considered to be high in all treatments, since C:N ratio was lower than 12:1. Organic matter fragmentation showed a higher amount of fulvic acids (FA), humic acids (HA) and humin (HU) in the PV treatment, for the three soil layers. The plantation on the sloping areas (PM) showed the highest values of (FA+HA)/HU ratio, suggesting a lower stability condition. Results suggest indigenous tree plantations have great potential to restore nutrient cycling and soil organic matter contents in short term period in areas where forests have been converted into pastures. Techniques to accelerate the development of trees plantation on the sloping areas must be adopted.

The use of Nodulated and Mycorrhizal Legume Trees for Land Reclamation in Mining Sites

The process of sucession in plant communities in degraded areas, following the initial disturbance may be described by: dispersion, establishment, competition, reaction and stabilisation. Dispersion is easily accomplished with human interference. Establishment depends on how plants germinate, grow and complete their cycle under harsh conditions. This depends on the microclimate, water-holding capacity of the soil or substrate, nutrients availability and the interaction of the plant with soil microorganisms. During primary colonisation, biological nitrogen fixation is extremely important. Then, mycorrhizal associations are important as litter accumulates and as it became the main source of nitrogen, phosphorus and other nutrients. The last three stages, competition, reaction and stabilisation, depend upon colonisation and will be a balance among pioneer and the less competitive successional species.

DECOMPOSIÇÃO DAS PODAS DAS LEGUMINOSAS ARBÓREAS Gliricidia sepium E Acacia angustissima EM UM SISTEMA AGROFLORESTAL

The 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, gliricidia sepium and Acacia angustissima , grown in alley cropping of banana ( Musa sp.) and “acai” 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 the usage of the legume Pueraria phaseoloides and nitrogen fertilization. The SAF implantation occurred in May 2004, at the Research Center of Embrapa Agrobiologia, in Seropedica, Rio de Janeiro State. The following year it was planted the forest African mahogany specie ( Kaya senegalensis ), at the centre of the legumes alleys. The experimental design was of randomized blocks with five treatments and four repetitions. The treatments consisted of the leguminous trees arranged between the lines of bananas and the “acai” palm, and they were: acacia angustissima ( Acacia angustissima ), tropical kudzu ( Pueraria phaseoloides ), and gliricidia (G liricidia sepium ); besides application of nitrogen as urea and spontaneous vegetation. To quantify the production of biomass, and the release of N, P, Ca, Mg and K, the legumes branches were cut and the kudzu tropical and spontaneous vegetation were mowed, in the rainy and dry seasons. The determination of remaining dry matter, releasing of nutrients, decomposition rates, and half life time of plant residues were held to 50 grams of fresh material from litterbags, placed on the soil surface, sampled at 0, 5, 10, 15, 20, 25, 30, 40, 60 and 75 days after the installation of the experiment. Acacia angustissima and kudzu tropical showed higher dry biomass, 9.5 and 10.8 Mg ha -1 , respectively. The gliricidia residues showed the highest decomposition rates, in the two year seasons.

A TWO-PHASE PROCESS FOR REVEGETATION OF ACIDIC BAUXITE TAILINGS IN THE AMAZON REGION, BRAZIL 1

This paper presents the methodology developed by the association of Mineracao Rio do Norte S.A. with Embrapa/Agrobiologia and the Soil Department of Federal University of Vicosa to promote revegetation of tailings ponds from bauxite mining in Porto Trombetas, Para State, Brazil. The tailings have a fine texture (77% clay), are low in nutrients, have low pH (4.5) and high P- fixation capacity. This technology is based upon a two-phase process. In the first phase, seeds of leguminous trees and shrubs, inoculated with N-fixing bacteria and mycorrhizae (VAM fungi), are hydroseeded over the tailings with fertilizer. This initial phase accelerates the tailings drying and incorporates carbon and nutrients into the tailings surface. In the second phase, after substrate consolidation, native secondary and pioneer species are planted with the objective of ensuring more biological diversity and sustainability in the system. Among the evaluated species, Sesbania virgata, S. exasperata, Cecropia sp., Parkia discolor, Styphnodendron guinensi, Leucaena leucocephala, Hidrocoria corumbosa and Chamaecrista flexuosa have been used with success in the first phase, and Sclerolobium paniculatum, Clitoria farchildian, Eugenia sp., Tapirira guyanensis, Dalbergia spruceana and Enterolobium maximum have been successful in the second phase. Four years after revegetation of the first tailings pond, monitoring results indicate a significant increase of biological activity in the substrate and the presence of different species from natural invasion and regeneration, indicating that primary successional processes are active. These results indicate that the two-phase revegetation process may be more appropriate for the tailings ponds in Porto Trombetas than conventional reclamation practices.

The use of leguminous trees in reclamation of tropical mined soils

Characterized as vigorous pioneer species which produce large amounts of biomass, forest leguminous trees have shown promise in studies of degraded soil rehabilitation. When associated with atmospheric nitrogen-fixing bacteria and mycorrhizal fungi, these species show superior utilization of nutrients and growth under adverse soil conditions. The objective of this paper is to present the principal results obtained from the Research Program for Use of Nodulated and Mycorrhizal Tree Legume Species in Rehabilitation of Degraded Areas, developed by National Research Center for Agrobiology-CNPAB/EMBRAPA in conjunction with the Federal University of Vicosa, Brazil. The program has been developed in four subprograms: (1) Field surveys to collect and identify native leguminous tree species with potential for land reclamation; (2) Selection to identify more efficient nitrogen-fixing bacteria for each potential species; (3) Greenhouse experiments to evaluate nutritional requirements and capacity to grow in high density soils; and (4) Field experiments in lands degraded by mining.

Macrofauna edáfica como indicadora em revegetação com leguminosas arbóreas

O trabalho foi desenvolvido em uma area de pasto abandonada revegetada com leguminosas arboreas. Localizada no municipio de Valenca, RJ, nela foram utilizadas diferentes proporcoes de leguminosas arboreas fixadoras de nitrogenio: 0% (0L), 25% (25L), 50% (50L) e 75% (75L). Para avaliacao da macrofauna do solo, as amostragens foram feitas nas epocas seca e umida, utilizando-se o metodo TSBF. Outras amostragens foram realizadas, ainda, em uma floresta secundaria (FS) e em duas areas de pasto (PA e PB). O processo de revegetacao aumentou a diversidade da fauna do solo de uma forma geral. Formicidae foi o grupo da macrofauna de maior abundância em todas as areas, para as duas epocas de avaliacao. Na epoca chuvosa, houve aumento consideravel na quantidade de invertebrados na camada serapilheira nos tratamentos 0L, 25L, 50L, 75L e Floresta Secundaria, o que no periodo seco aconteceu na camada 0-10 cm.