The thesis objective was to evaluate the forms of accumulation and release of phosphorus from cover crops waste under long time of different soil management systems and its relationship with the soil phosphorus forms. The experiment was established in 1986 on an Oxisol in the IAPAR experimental station in Pato Branco, Paraná State, Brazil. The treatments consisted of six winter cover crops (blue lupine, vetch, oats, radish, rye and wheat) and the winter fallow treatment, cultivated under no-tillage (NT) and conventional (CT). In September 2011 were collected soil samples (0-5 and 5-10 cm) and the shoots of winter cover crops. Confected litterbags (0.2 x 0.2 m) were collected at 7, 14, 28, 56 and 112 days after the cover crops management. In the residues collected, we assessed the accumulation of C, N, P, and held the fractionation of P. In the soil samples, we made the separation of aggregates by wet way and in the original soil and aggregates we evaluated the content of total C, N, P, the P forms, and the acid phosphatase activity. The distribution of P forms in the cover crops tissue varies among species and their accumulation was a function of nutrient soil P availability, as in NT. But for all of them, the soluble inorganic P was the principal storage form. The release of P from plant residues depends not only on its rate of decomposition, but also on the content of total and soluble P. The vetch and rye have great potential to recycle soil P, and this amount of P should be considered when prescribing phosphorus fertilization for the culture implanted in sequence. However, the long term cultivation of different winter cover crops did not affected the soil P forms in highly weathered clay soils, managed under NT and CT. On the other hand, practices that favor the accumulation of organic residues on the soil surface as the NT system, increase the acid phosphatase enzyme activity and labile organic and inorganic P forms, besides the formation of larger aggregates, which have higher levels of C, N, total P and organic labile P. / O objetivo desta tese foi avaliar as formas de acúmulo e liberação de fósforo dos resíduos de plantas de cobertura sob diferentes sistemas de manejo de solo por longa duração e sua relação com as formas de fósforo no solo. O experimento foi instalado em 1986 sobre um Latossolo Vermelho distroférrico da estação experimental do IAPAR em Pato Branco, estado do Paraná. Os tratamentos consistem em seis plantas de cobertura de inverno (tremoço azul, ervilhaca comum, aveia preta, nabo forrageiro, centeio e trigo) mais uma parcela que permanece em pousio no período de inverno, manejadas sob sistema plantio direto (SPD) e sistema de cultivo convencional (SCC). Em setembro de 2011, coletaram-se amostras de solo (0-5 e 5-10 cm) e da parte aérea das plantas de cobertura de inverno. Confeccionaram-se bolsas de decomposição (0,2 x 0,2m), que foram coletadas aos 7, 14, 28, 56 e 112 dias após o manejo das plantas de cobertura. Nos resíduos coletados, avaliou-se o acúmulo de C, N, P e o realizou-se o fracionamento do P. Nas amostras de solo, realizou-se a separação de agregados por via úmida e, no solo original e nos agregados, realizou-se a avaliação dos teores de C, N, P e o fracionamento de P, e da atividade de fosfatase ácida. A distribuição das formas de P no tecido das plantas de cobertura varia entre as espécies e a sua acumulação foi função da disponibilidade de P no solo. Mas, para todas elas, o P inorgânico solúvel foi a principal forma de armazenamento. A liberação de P dos resíduos das plantas de cobertura não depende apenas da sua taxa de decomposição, mas também do teor total e solúvel de P. A ervilhaca comum e o centeio possuem grande potencial para reciclar P do solo, sendo que essa quantidade de P deve ser considerada na prescrição da adubação fosfatada da cultura implantada em sequência. Contudo, o cultivo de plantas de cobertura de inverno por longo período não alterou as formas de P em solo argiloso altamente intemperizado, manejado sob SPD e sob SCC. Por outro lado, práticas que propiciem o acúmulo de resíduos orgânicos na superfície do solo, como o SPD, elevam a atividade de fosfatase ácida e as formas lábeis orgânicas e inorgânicas de P, além da formação de agregados maiores, os quais apresentam teores mais elevados de C, N, P total e P orgânico lábil.

Cette étude repose sur une analyse comparative des distributions d’éléments traces (ET) dans les podzols de deux forêts adjacentes qui se distinguent principalement par leur régime de perturbation. La forêt du site de l’Île a été protégée des perturbations majeures pendant plusieurs siècles, tandis que le site du Versant a subi un feu majeur il y a 100 ans. Bien qu’ils aient évolué à partir du même matériel parental et sous les mêmes conditions climatiques et topographiques, les sols de ces deux sites présentent des différences marquées au niveau de leur morphologie et de leurs propriétés chimiques. Notamment, le sol de l’Île, qui est dominée par des conifères, a un pH significativement plus faible dans l’entièreté du profil, un horizon B podzolique qui contient significativement plus d’oxydes de fer cristallin et des horizons organiques quatre fois plus épais en comparaison au sol du Versant, un peuplement de feuillus. L’objectif de ce projet de recherche était alors de démontrer comment les différentes conditions biogéochimiques affectent la rétention et la mobilisation des ET et plus spécifiquement, comment l’âge des forêts affecte le cycle des ET à travers son influence sur la pédogénèse. Dans chacun des deux sites, quatre pédons ont été creusés puis tous leurs horizons de sol ont été échantillonnés (total de 79 échantillons) afin de mesurer leurs concentrations extraites à l’acides et solubles dans l’eau en As, Cd, Cu, Pb, V et Zn. Les différences majeures entre les deux sites se trouvaient surtout dans les horizons organiques, où les concentrations totales de tous les ET étaient significativement plus élevées sur le Versant. Un cyclage biologique accru sur le Versant, par la présence de feuillus, dont Betula alleghaniensis, explique en partie les concentrations élevées dans la couche d’humus, particulièrement pour le Cd, le Cu et le Zn, dont les concentrations étaient jusqu’à 5 fois plus élevées dans l’horizon F du Versant. Cependant, le pourcentage d’ET en solution était significativement plus élevé sur l’Île pour tous les ET, à l’exception de l’As. Le très faible pH de l’Île a contribué à la mobilisation de ces ET. La rétention de Cd et de Zn était plus sensible à la variation de pH que les autres ET. Une quantité significative de Zn a été lessivée en dehors du profil de la forêt non-perturbée, car le stock total du profil de sol en Zn (mg/m2 par cm d’épaisseur) y est 4.5 fois plus faible que sur le Versant. Cette étude soulève l’impact direct et indirect de la dynamique de la végétation sur la pédogénèse et sur le cycle des ET dans les podzols. / This study is based on a comparative analysis of the distribution of trace elements (ET) in the podzolic soils of two adjacent forested sites that distinguish themselves based on their disturbance regime. The Island site was sheltered from major disturbances for several centuries, whereas a stand-replacing wildfire burned the area 100 years ago on the Hillslope site. Even though the soils of both sites developed from the same parent material and under the same climatic and topographic conditions, they display major morphological and chemical differences. The Island is a coniferous stand that has a significantly lower soil pH through the entire profile, a podzolic B horizon that contains significantly more crystalline iron oxide and organic horizons that are four times thicker than at the Hillslope, a deciduous stand. The objective of this research is to demonstrate how different biogeochemical conditions affect the retention and mobilisation of TE and more specifically how stand age influences the cycling of TE in soils through its impact on pedogenesis. In each site, four soil profiles were dug and all their horizons were sampled (total of 79 samples) in order to measure their acid-extracted and water-soluble concentrations of As, Cd, Cu, Pb, V and Zn. Major differences between the two sites are mainly found in organic horizons, where acid-extracted TE concentrations were significantly greater on the Hillslope. The enhanced biocycling caused by deciduous trees including Betula alleghaniensis contributed to the high concentrations in the humus layer of the Hillslope, especially of Cd, Cu and Zn, which were 5 times higher in the F horizon compared to the Island. Also, a higher percentage of TE was soluble on the Island for all TE, except for As. The solubilisation of TE was associated to the low soil pH of the older stand. Cd and Zn retention were more sensible to pH variation than other TE. A significant quantity of Zn was leached outside of the soil profile on the Island since the summed Zn content of the entire profile (mg Zn /m2 surface /cm thickness) was 4.5 times lower than on the Hillslope. This study highlights the direct and indirect impacts of vegetation on soil genesis and TE cycling in podzols.