Phosphorus (P) is an essential plant nutrient and is one of the most critical elements influencing crop production throughout the world. Phosphorus deficiency is widespread in most soils of northern Ghana, and ferruginous nodules contained in some soils in the region accentuate the deficiency problem because they act as P sinks. This research focuses on P fertility status of soils in landscapes common to northern Ghana. Three sites were selected for the study and were referred to as sites 1, 2 and 3. Soils in a catenary sequence from site 1 were sampled for detailed P distributions in profiles, and surface soils from the upper, mid and lower slope positions of the other landscapes (sites 2 and 3) were used. The nature of P in the soil fines and ferruginous nodules was investigated using a modified Hedley fractionation procedure. The objective was to quantify the labile and non-labile inorganic P (Pi) and organic P (Po) in relation to pedogenic weathering processes at different slope positions at site 1. A secondary objective was to assess the P distribution in the landscapes at sites 2 and 3. The largest P fraction in both soil fines and nodules at each site was resistant non-labile P forms. Primary P (Ca-P) decreased with depth in the profile at the upper slope position but it occurred in greater quantities in C horizons of the lower slope soils. Phosphorus sorption capacity of the soil fines and nodules was determined to predict the behaviour of P fertilizers in the soils. Phosphorus sorption by the soil fines increased to a maximum in the B horizon of each profile and a t-test showed that P sorption was similar in profiles at each slope position. The P sorption capacities of uncrushed ferruginous nodules varied according to their sizes. The small nodules were more reactive and sorbed more P than the larger sizes. Fractionation of P from the nonfertilized and fertilized soils at the end of cropping and anion exchange resin (AER) extraction, revealed that there had been redistribution of P into different fractions. A comparison of P fractions of the nonfertilized soils after the AER extraction with those of the native soil P showed decreases in some native labile and non-labile P fractions. This suggested that these P fractions could be available for plant uptake. Both 50% PAPR and SSP fertilizations increased the labile Pi and NaOH extractable Pi levels in the soils. (Abstract shortened by UMI.)

Intensive forest management techniques such as whole-tree harvesting and use of herbicides to control weeds can have an effect on nutrient cycling and nutrient pool sizes in the mineral soil. This study was conducted to measure differences in soil carbon (C), nutrient pools, or phosphorus (P) fractions associated with harvest-intensity (bole-only vs. whole-tree harvest) and weed-control treatments (initial weed control vs. five years of annual weed control) after ten years. Soil C, nitrogen (N), and P, and exchangeable calcium (Ca), potassium (K), magnesium (Mg), and Hedley P fractions were measured prior to treatment establishment and after ten years in two Douglas-fir (Pseudotsuga menziesii) plantations in the Pacific Northwest. We observed increases in most nutrient concentrations with initial weed control compared with annual weed control at Matlock, with opposite trends at Molalla. Exchangeable Ca and Mg content showed responses to weed control treatments. Harvesting treatments had no significant effects on soil C and nutrient pools at either site. Total P and many of the Hedley P fractions decreased over time, but these effects were ameliorated with the less-intensive initial-weed-control-only treatment at Matlock and the more-intensive annual-weed-control at Molalla. Ten-year responses suggest that harvesting intensity has not impacted potential for maintaining soil C and nutrient pools, with the exception of P, for long-term productivity. Knowledge of the on-site vegetative communities and their role in nutrient cycling is required to anticipate what effect weed control might have on nutrient pools through ensuing stand development. / Master of Science

Phosphorus is the main limiting nutrient for plant growth in large areas of the world and the availability of phosphorus to plants and microbes can be strongly affected by soil properties. Even though the phosphorus cycle has been studied extensively, much remains unknown about the key processes governing phosphorus availability in different environments. In this thesis the complex dynamics of soil phosphorus and its availability were studied by relating various phosphorus fractions and soil characteristics to microbial respiration kinetics. The soils used represent a range of aluminium, iron, carbon and total phosphorus content, and were located in four different biomes: subtropical forest, warm temperate forest, boreal forest and tundra. The results showed that NaOH extractable phosphorus, a fraction previously considered to be available to plants only over long time scales, can be accessed by microbes in days or weeks. Microbial phosphorus availability was not related to aluminium or iron content in any of the studied systems, not even in highly weathered soils with high aluminium and iron content. This is in contrast with other studies of soils with high sorption capacity and shows the variability of factors that govern phosphorus availability in different environments. In the boreal forest chronosequence, no difference could be seen with age in total phosphorus content or concentrations of occluded phosphorus forms. However, there were lower concentrations of labile phosphorus forms in older systems, which were correlated with a decrease in microbial respiration. This was most likely related to organic matter quality in the system, and not to geochemical factors. Phosphorus availability was linked to differences in topography (water regime) and vegetation in the tundra ecosystems. The results suggest that the availability of phosphorus, both for microbes and plants, was lower on the meadow vegetation sites compared to the two types of heath vegetation. Many factors are important for phosphorus availability in soils, but these results suggest that microbes can access less available phosphorus if not restricted by carbon, and this may be important in regard to forest management practices as well as effects of environmental change.

Submitted by Claudia Rocha (claudia.rocha@udesc.br) on 2018-03-21T16:56:36Z No. of bitstreams: 1 PGCS12DA031.pdf: 1064335 bytes, checksum: d022b9552e24f8051aefd3e5284d93dd (MD5) / Made available in DSpace on 2018-03-21T16:56:36Z (GMT). No. of bitstreams: 1 PGCS12DA031.pdf: 1064335 bytes, checksum: d022b9552e24f8051aefd3e5284d93dd (MD5) Previous issue date: 2012-05-04 / Capes / In soils of low fertility and commonly not fertilized, it is assumed that during the development of forest species, stands they can absorb less labile forms of nutrients. This situation implies on more specific soil analysis because the classical methods estimate only the readily available nutrients, difficulting the diagnosis of soil fertility and fertilizer recommendation for forests. The objective of this study was to analyze labile and non-labile forms of carbon (C), phosphorus (P), potassium (K), calcium (Ca) and magnesium (Mg) of soil in forests of Pinus taeda in the first rotation (17 years of cultivation) and third rotation (49 years of continuous pine cultivation) in different soil layers up to 80 cm depth. The relative content of soil carbon in fulvic acid decreased from first to third rotation and humic acids increased from first to third rotation, indicating that with the increase of time use with forests, there is the transformation of more labile carbon in more stable forms. These results show that the total organic carbon may not be a good indicator of the changes in the soil carbon dynamics under pine forests, and that fractions of organic matter may be more reliable. With time, the moderately labile inorganic P acted as a sink of soil P, increasing its levels from first to third rotation, while the labile inorganic (Pi-Pi-RTA and NaHCO3) and labile organic (Po-NaHCO3) acted as a source of P, suggesting that the analysis of available P in soils under pine forests should take into account these fractions. The soil on older use with pine forest showed lower levels and stocks of K, Ca and Mg and non-exchangeable Ca and K. Both, P, K and Mg showed great reserve in non-labile forms that may be available in the long term, unlike Ca, which showed labile and total concentrations too low. Thus, while the available forms of P, K and Mg could be replenished by other forms of these nutrients in the soil, regardless of replenishment through fertilization, the export of Ca by wood without its replacement may drastically limit the Ca supply for next pine rotations / Em solos de baixa fertilidade e comumente não fertilizados, supõe-se que as espécies florestais podem absorver formas menos lábeis de nutrientes que são disponibilizados ao longo da rotação florestal. No entanto a avaliação desta situação é complexa, pois os métodos clássicos estimam apenas os teores prontamente disponíveis, dificultando o diagnóstico da fertilidade do solo e a definição da necessidade de adubação. O objetivo deste trabalho foi analisaros teores e estoques de diferentes formas decarbono, fósforo, potássio, cálcio e magnésio do solo em florestas de Pinus taeda L. em primeira rotação (17 anos de cultivo) e terceira rotação (49 anos de cultivo sucessivo) em diferentes camadas do solo até 80 cm de profundidade. O solo em terceira rotação teve seu conteúdo relativo de carbono em ácidos fúlvicos menor e o de ácidos húmicos maior, quando comparado à floresta em primeira rotação, indicando que com o aumento do tempo de uso com florestas há a transformação de formas mais lábeis de carbono em formas mais estáveis. Os teores totais não são bons indicadores de modificações do C na superfície do solo e as frações da matéria orgânica podem ser utilizadas para diagnosticar a dinâmica da matéria orgânica do solo em florestas de Pinus. A fração de P inorgânico moderadamente lábil (Pi-NaOH) foi 47% maior na floresta em 3ª rotação de Pinus, enquanto as frações inorgânicas lábeis (Pi-RTA e Pi-NaHCO3) e orgânicas lábeis (Po-NaHCO3) foram maiores nos solos sob primeira rotação, sugerindo a existência de uma modificação das formas de fósforo e que, diferentes formas desse nutriente podem contribuir com a disponibilidade de P em solos sob florestas de Pinus. A floresta há mais tempo cultivada com Pinus taeda apresentou menores teores e estoques de K trocável (extraído por NH4OAc.), Ca e Mg trocáveis (KCl), K não-trocável (HNO3) e de Ca semi-total (Água régia). Tanto o P como o K e Mg apresentaram grande reserva em formas não lábeis (ou não trocáveis e semitotais) que poderão vir a ser disponibilizadas em longo prazo, diferentemente do Ca, que apresentou teores lábeis e totais muito baixos. Assim, enquanto as formas disponíveis de P, K e Mg poderiam ser reabastecidas por outras formas destes nutrientes no solo, independente de reposição via fertilização, a exportação sem nenhuma reposição de Ca poderá limitar drasticamente a disponibilidade deste nutriente no solo

Made available in DSpace on 2016-12-08T15:50:06Z (GMT). No. of bitstreams: 1 PGCS12DA031.pdf: 1064353 bytes, checksum: 3650d4bc597fa05d242856c40e92363a (MD5) Previous issue date: 2012-05-04 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / In soils of low fertility and commonly not fertilized, it is assumed that during the development of forest species, stands they can absorb less labile forms of nutrients. This situation implies on more specific soil analysis because the classical methods estimate only the readily available nutrients, difficulting the diagnosis of soil fertility and fertilizer recommendation for forests. The objective of this study was to analyze labile and non-labile forms of carbon (C), phosphorus (P), potassium (K), calcium (Ca) and magnesium (Mg) of soil in forests of Pinus taeda in the first rotation (17 years of cultivation) and third rotation (49 years of continuous pine cultivation) in different soil layers up to 80 cm depth. The relative content of soil carbon in fulvic acid decreased from first to third rotation and humic acids increased from first to third rotation, indicating that with the increase of time use with forests, there is the transformation of more labile carbon in more stable forms. These results show that the total organic carbon may not be a good indicator of the changes in the soil carbon dynamics under pine forests, and that fractions of organic matter may be more reliable. With time, the moderately labile inorganic P acted as a sink of soil P, increasing its levels from first to third rotation, while the labile inorganic (Pi-Pi-RTA and NaHCO3) and labile organic (Po-NaHCO3) acted as a source of P, suggesting that the analysis of available P in soils under pine forests should take into account these fractions. The soil on older use with pine forest showed lower levels and stocks of K, Ca and Mg and non-exchangeable Ca and K. Both, P, K and Mg showed great reserve in non-labile forms that may be available in the long term, unlike Ca, which showed labile and total concentrations too low. Thus, while the available forms of P, K and Mg could be replenished by other forms of these nutrients in the soil, regardless of replenishment through fertilization, the export of Ca by wood without its replacement may drastically limit the Ca supply for next pine rotations / Em solos de baixa fertilidade e comumente não fertilizados, supõe-se que as espécies florestais podem absorver formas menos lábeis de nutrientes que são disponibilizados ao longo da rotação florestal. No entanto a avaliação desta situação é complexa, pois os métodos clássicos estimam apenas os teores prontamente disponíveis, dificultando o diagnóstico da fertilidade do solo e a definição da necessidade de adubação. O objetivo deste trabalho foi analisaros teores e estoques de diferentes formas decarbono, fósforo, potássio, cálcio e magnésio do solo em florestas de Pinus taeda L. em primeira rotação (17 anos de cultivo) e terceira rotação (49 anos de cultivo sucessivo) em diferentes camadas do solo até 80 cm de profundidade. O solo em terceira rotação teve seu conteúdo relativo de carbono em ácidos fúlvicos menor e o de ácidos húmicos maior, quando comparado à floresta em primeira rotação, indicando que com o aumento do tempo de uso com florestas há a transformação de formas mais lábeis de carbono em formas mais estáveis. Os teores totais não são bons indicadores de modificações do C na superfície do solo e as frações da matéria orgânica podem ser utilizadas para diagnosticar a dinâmica da matéria orgânica do solo em florestas de Pinus. A fração de P inorgânico moderadamente lábil (Pi-NaOH) foi 47% maior na floresta em 3ª rotação de Pinus, enquanto as frações inorgânicas lábeis (Pi-RTA e Pi-NaHCO3) e orgânicas lábeis (Po-NaHCO3) foram maiores nos solos sob primeira rotação, sugerindo a existência de uma modificação das formas de fósforo e que, diferentes formas desse nutriente podem contribuir com a disponibilidade de P em solos sob florestas de Pinus. A floresta há mais tempo cultivada com Pinus taeda apresentou menores teores e estoques de K trocável (extraído por NH4OAc.), Ca e Mg trocáveis (KCl), K não-trocável (HNO3) e de Ca semi-total (Água régia). Tanto o P como o K e Mg apresentaram grande reserva em formas não lábeis (ou não trocáveis e semitotais) que poderão vir a ser disponibilizadas em longo prazo, diferentemente do Ca, que apresentou teores lábeis e totais muito baixos. Assim, enquanto as formas disponíveis de P, K e Mg poderiam ser reabastecidas por outras formas destes nutrientes no solo, independente de reposição via fertilização, a exportação sem nenhuma reposição de Ca poderá limitar drasticamente a disponibilidade deste nutriente no solo