Resumen Los cambios en el uso del suelo provocan un mosaico de áreas en el paisaje con diferentes usos y coberturas. Esta condición compromete las reservas de nutrientes del suelo, especialmente el fósforo (P). En ese sentido, este estudio tuvo como objetivo determinar las concentraciones de fósforo extraíble y total en 04 clases de suelo (Argisol Amarillo, Neosol Litólico, Entisol y Planosol), 04 usos y coberturas del suelo (Caatinga Nativa Abierta, Caatinga Nativa Densa, Agricultura y Pastos), en 04 profundidades (0-10, 10-20, 20-30 y 30-40 cm). Para determinar el P extraíble se utilizó el Mehlich 1 y la lectura colorimétrica. El fósforo total se determinó por digestión de azufre y colorimetría. Los resultados de las concentraciones de P extraíble y total fueron mayores para las clases Argisol y Planosol. Se observó que hubo reducciones en las concentraciones de P extraíble entre las capas del suelo a medida que se profundizaba el perfil del suelo. Las profundidades entre 0 y 20 cm generalmente mostraron concentraciones más altas de fósforo extraíble y total en la agricultura. Entre las cuatro clases de suelo estudiadas, los valores promedio más altos de existencias de P extraíble y total se presentaron en los Neosoles y Planosoles Litólicos, principalmente debido al uso agrícola. La deficiencia de P ha sido un factor limitante para la productividad agrícola y, especialmente en la región de Agreste de Pernambuco, donde las principales clases de suelo con cobertura natural tienen niveles bajos de P disponible y total.

Abstract Changes in land use cause a mosaic of areas in the landscape with different uses and coverage. This condition compromises soil nutrient stocks, especially phosphorus (P). In this sense, this study aimed to determine the concentrations of extractable and total phosphorus in 04 soil classes (Yellow Argisol, Litholic Neosol, Entisol and Planosol), 04 uses and covers (Open Native Caatinga, Dense Native Caatinga, Agriculture and Pasture) of the soil, in 04 depths (0-10, 10-20, 20-30 and 30-40 cm). To determine the extractable P, the Mehlich 1 and colorimetric reading were used. Total phosphorus was determined by sulfur digestion and colorimetry. The results of extractable and total P concentrations were higher for the Argisol and Planosol classes. It was observed that there were reductions in extractable P concentrations between the soil layers as the soil profile deepened. Depths between 0-20 cm generally showed higher concentrations of extractable and total phosphorus in agriculture. Among the four soil classes studied, the highest average values of extractable and total P stocks occurred in Litholic Neosols and Planosols, mainly due to agricultural use. P deficiency has been a limiting factor to agricultural productivity and, especially in the Agreste region of Pernambuco, where the main soil classes under natural cover have low levels of available and total P.

Resumo O principal processo natural que se contrapõe ao Efeito Estufa é chamado de sequestro de carbono, um fenômeno que essencialmente busca estabelecer um equilíbrio dinâmico entre a emissão dos gases do efeito estufa (GEE) a partir da imobilização de seus elementos, especialmente do C e N. O presente trabalho teve como objetivo principal avaliar os estoques de C e N em solo da região semiárida do Brasil submetido a irrigação com água residual tratada de esgoto doméstico. Para isso, o estoque de carbono e nitrogênio do solo soram comparados para quatro diferentes usos: caatinga nativa aberta (ONC); irrigação com água residual tratada (TSEI); irrigação com água superficial (SWI); e agricultura de sequeiro (TRA). A hipótese levantada na pesquisa foi de que o reuso de efluentes tratados na agricultura, além de ser uma alternativa que pode mitigar a problemática de escassez hídrica da região semiárida, também é capaz de influenciar a capacidade de estocar C e N no solo devido a sua carga orgânica. Os resultados indicaram que entre os diferentes usos de solos avaliados, os estoques de C e N no solo foi maior na ONC diminuindo com o uso do solo para a agricultura. O maior acúmulo de C e N na caatinga deve-se a presença de serrapilheira, não sendo detectado, no presente estudo, influência da irrigação com efluente de esgoto tratado. Conclui-se que o aporte de resíduos de vegetação na superfície do solo vem a ser o fator de maior contribuição para a estocagem de carbono e nitrogênio nos solos estudados.

Abstract The main process that opposes the Greenhouse Effect is called “carbon sequestration”, a phenomenon that essentially seeks to establish a dynamic balance between greenhouse gas (GHG) emissions from the immobilization of its elements, especially C and N. This work evaluated the stocks of carbon and nitrogen in soils of the Brazilian semi-arid submitted to irrigation with treated wastewater from domestic sewage. For this purpose, the carbon and nitrogen stocks in the soil of the semi-arid region of Brazil were compared for four different uses: Open Native Caatinga (ONC); Treated Wastewater Effluent Irrigation (TSEI); Surface Water Irrigation (SWI); and Traditional Rainfed Agriculture (TRA). The hypothesis considered in this research was that the application of treated effluents in agriculture, besides being an alternative that can mitigate the problem of water scarcity of the semiarid region, is also capable of influencing the storage capacity of C and N in the soil, due to its organic load. The results indicate that among the different land uses evaluated, soil C and N stocks were highest in ONC, and decreased with the agricultural land use. The greatest accumulation of C and N in Caatinga is due to the presence of forest litter, and the influence of irrigation with treated sewage effluent was not detected in the present study. It can be concluded that the contribution of vegetation residues to the soil surface is the main factor contributing to C and N storage.