One sentence summary: 2Previously unreported forest areas in dryland biomes increase current estimates of the 3 global forest cover by at least 9 %. 4 List of authors:

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Unprecedenteded rates of deforestation and biomass burning in tropical dry forests are dramatically influencing biogeochemical cycles, resulting in resource depletion, declines in biodiversity, and atmospheric pollution. We quantified the effects of deforestation and varying levels of slash—fire severity on nutrient losses and redistribution in a second—growth tropical dry forest ("Caatinga") near Serra Talhada, Pernambuco, Brazil. Total aboveground biomass prior to burning was °74 Mg/ha. Nitrogen and phosphorous concentrations were highest in litter, leaves attached to slash, and fine wood debris (<0.64 cm diameter). While these components comprised only 30% of the prefire aboveground biomass, they accounted for °60% of the aboveground pools of N and P. Three experimental fires were conducted during the 1989 burning season. In these treatments consumption was 78, 88, and 95% of the total aboveground biomass. As much as 96% of the prefire aboveground N and C pools and 56% of the prefire aboveground P pool was lost during combustion processes. Nitrogen losses exceeded 500 kg/ha and P losses exceeded 20 kg/ha in the fires of the greatest severity. With increasing fire severity, the concentrations of N and P in ash decreased while the concentration of Ca increased. This indicates greater amounts of these nutrients were volatilized (i.e., greater ecosystem losses occurred) with increasing fire severity. Following fire, up to 47% of the residual aboveground N and 84% of the residual aboveground P were in the form of ash, which was quickly lost from the site via wind erosion. Fires appeared to have a minor immediate effect on total N, C, or P in the soils. However, soils in forests with no history of cultivation had significantly higher concentrations of C and P than second—growth forests. Based upon the measured losses of nutrients from these single slash—burning events, it would likely require a century or more of fallow for reaccumulation to occur. However, current fallow periods in this region are 15 yr or less.

Resumo -Os objetivos deste trabalho foram quantificar as concentrações de carbono e nutrientes em solos de áreas adubadas e não adubadas com esterco; quantificar as concentrações de nutrientes em amostras de esterco bovino utilizado na região e calcular o acúmulo de nutrientes resultantes dessa adubação e o potencial de perdas por lixiviação. Foram amostradas 18 áreas agrícolas, com adição anual de esterco por pelo menos dois anos e, como controle, quatro áreas sob pastagem não adubadas, coletando-se amostras de solo das camadas de 0-20, 20-40 e 40-60 cm, que foram analisadas quanto à granulometria, densidade do solo, pH, C, N e P totais, bases trocáveis, P extraível por água e por Mehlich-1. Amostras de esterco utilizadas em nove áreas também foram analisadas. A aplicação de esterco resultou em acumulações médias ao redor de 20 Mg ha -1 de C, 2 Mg ha -1 de N total e Ca, e de 0,5 a 1 Mg ha -1 de P total, K e Mg (0-60 cm). Acumulações de P solúvel em água e bases trocáveis na camada de 40-60 cm, em relação às testemunhas, indicam grande potencial de perda desses nutrientes.Termos para indexação: agricultura familiar, adubação orgânica, lixiviação de fósforo. Nutrient build up in sandy soils receiving manure additionsAbstract -The objective of this work was to quantify changes on carbon and nutrient contents in soils under continuous manure additions. Eighteen cropped fields that had received annual additions of manure for at least two years and four fields under pasture with no history of manure addition were sampled to assess if this practice results in the accumulation or losses of added nutrients. Soils samples from the 0-20, 20-40 and 40-60 cm layers were taken from each field, and analyzed with regard to their physical (particle size and soil density) and chemical (pH, total C, N and P, extractable P by Mehlich-1 and water, and exchangeable cations) properties. Manure samples used in nine fields were also analyzed for chemical composition. Manure additions resulted in a build up of nutrient stocks near to 20 Mg ha -1 of C, 2 Mg ha -1 of N and Ca, and 0.5 to 1 Mg ha -1 of P, K and Mg (0-60 cm). Water-soluble P concentrations of 7 mg kg -1 in the 40-60 cm layer indicated losses of this nutrient, the less mobile in soils. Accumulation of exchangeable cations in the 0-60 cm layer, in comparison with control areas, indicates an even greater potential for losses of these nutrients.

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