Nos solos tropicais intemperizados há elevada adsorção de fósforo, tornando o nutriente pouco disponível. A principal estratégia para aumento dos teores de fósforo no solo é a adubação fosfatada, porém cerca de 80% do total do nutriente aplicado no solo torna-se indisponível. A adição de matéria orgânica tem importância na diminuição da adsorção de fósforo devido a formação de substâncias húmicas, que bloqueiam os sítios adsorção além de atuar sobre os sais insolúveis de fósforo. Entretanto, para estes efeitos benéficos há a necessidade da adição de grandes quantidades de tais componentes orgânicos o que resultaria em problemas econômicos e logísticos aos produtores. Tentando solucionar este problema foram criados também os superfosfatos orgânico-complexados (SOC), os quais têm em sua composição a presença de agentes quelantes orgânicos (ácidos húmicos) complexados ao fosfato monocálcio através de pontes metálicas com cálcio, ferro ou alumínio, ou dois destes metais simultaneamente. A justificativa para a eficiência deste produto é que a formação de complexos fósforo-metal-ácidos orgânicos diminui a fixação de fósforo no solo, incrementando assim o aproveitamento do fertilizante fosfatado pelas culturas. Para verificar estes efeitos realizou-se experimento em casa de vegetação e campo, respectivamente intitulados: (i) \"Frações de fósforo no solo mediante a aplicação de superfosfato orgânicocomplexado\" e \"(ii) Uso do superfosfato orgânico-complexado na cultura da cana-de-açúcar\". O objetivo geral do trabalho foi avaliar o efeito da aplicação do SOC na adsorção de fósforo em solos com textura contrastantes submetidos ou não, a correção de acidez e na nutrição da cultura da cana-de-açúcar. No experimento em casa de vegetação verificou-se em solo arenoso e argiloso, com e sem correção de acidez, o efeito da aplicação dos fertilizantes orgânico-complexados nas frações de fósforo do solo através do fracionamento proposto por Hedley. No solo arenoso a maior parte do fósforo aplicado via fertilizante permanece nas frações inorgânicas lábeis as quais tem aumento em função da aplicação do superfosfato orgânico-complexado, além do efeito sinérgico deste com a prática da calagem. No solo argiloso a aplicação do SOC aumenta as formas de fósforo orgânico lábil no solo, além, pela interação sinérgica com a correção da acidez, de diminuir a quantidade de fósforo inorgânico quimiossorvido a ferro e alumínio. O experimento em campo avaliou os efeitos da aplicação de superfosfato orgânico-complexado (SOC) e superfosfato simples (SFS), nas doses de 0, 45, 90, 135 e 180 kg ha-1 de P2O5 em cana planta, além da reaplicação da dose 45 kg ha-1 de P2O5 na soqueira, apenas nos tratamentos que anteriormente receberam 45 e 90 kg ha-1. Em cana planta a aplicação do SFS aumenta a massa de matéria seca de colmo devido a aplicação de níveis crescentes de P2O5, enquanto o uso do SOC não apresentou nenhuma influência, além de promover menor acúmulo de fósforo nesta parte da planta. Na soqueira, a produtividade de colmos industrializáveis e o acúmulo de massa seca no colmo não tem efeito da aplicação dos fertilizantes, porém há menor acúmulo de matéria seca, nitrogênio e fósforo no ponteiro com o uso do fertilizante orgânico-complexado. / In weathered tropical soils there is high phosphorus adsorption, turning the nutrient less available. The main strategy for increasing the levels of phosphorus in the soil is through phosphate fertilization, however 80% of the total nutrient applied to the soil becomes unavailable. The addition of organic matter is important in reducing the phosphorus adsorption due to the formation of humic substances which block the adsorption sites in addition to acting on the insoluble phosphate salts. However, for these beneficial effects there is a need of adding quite large amounts of organic compounds which would result in economical and logistic problems to the producers. Trying to solve this problem the organiccomplexed superphosphate (OCS), which have in their composition the presence of organic chelators (humic acids) complexed with monocalcium phosphate through metal bonds with calcium, iron or aluminum, or two of these metals simultaneously. The reason for the efficiency of this product is that the formation of the complex phosphorus-metal-organic acids inhibits the fixation of phosphorus in the soil, thereby increasing the use of phosphate fertilizer by crops. To verify these effects, it was performed an experiment in the greenhouse and field, respectively entitled: (i) \"Phosphorus fractions in soil by application of organiccomplexed superphosphate\" and \"(ii) organic-complexed superphosphate in the culture of cane sugarcane \". The overall objective was to evaluate the effect of the application of OCS in phosphorus adsorption in soils with contrasting textures submitted or not to the correction of acidity and also in the nutrition of cane sugar. In the greenhouse experiment, it was verified in sandy and loamy soil, with and without correction of acidity, the effect of application of organic-complexed fertilizers on soil phosphorus fractions by fractionation proposed by Hedley. In the sandy soil most of the phosphorus applied via fertilizer remained in the labile organic fractions which increase due to the application of the organic super-complexed phosphate, in addition to the synergistic effect to the practice of lime. In clay soil the application of OCS increased the forms of labile organic phosphorus in the soil, besides its synergistic interaction with the soil acidity decreasing the amount of inorganic phosphorus chemically fixed on iron and aluminum. The field experiment evaluated the effects of organic-complexed superphosphate (OCS) and simple superphosphate (SS) applications at doses of 0, 45, 90, 135 and 180 kg ha-1 of P2O5 in plant cane, but the reapplication of the 45 kg ha-1 of P2O5 dose on ratoon was only in treatments that previously received 45 and 90 kg ha-1. In plant cane the application of SFS increased stalk dry matter due to the application of crescent levels of P2O5, while the use of OCS had no influence, in addition to promoting lower phosphorus accumulation in this part of the plant. In the ratoon, the productivity of industrialized stalks and dry matter accumulation in the stem had no effect through fertilizer application, but there were lower accumulation of dry matter, nitrogen and phosphorus matter in the growing point with the use of organic-complexed fertilizer.

Nos solos tropicais intemperizados há elevada adsorção de fósforo, tornando o nutriente pouco disponível. A principal estratégia para aumento dos teores de fósforo no solo é a adubação fosfatada, porém cerca de 80% do total do nutriente aplicado no solo torna-se indisponível. A adição de matéria orgânica tem importância na diminuição da adsorção de fósforo devido a formação de substâncias húmicas, que bloqueiam os sítios adsorção além de atuar sobre os sais insolúveis de fósforo. Entretanto, para estes efeitos benéficos há a necessidade da adição de grandes quantidades de tais componentes orgânicos o que resultaria em problemas econômicos e logísticos aos produtores. Tentando solucionar este problema foram criados também os superfosfatos orgânico-complexados (SOC), os quais têm em sua composição a presença de agentes quelantes orgânicos (ácidos húmicos) complexados ao fosfato monocálcio através de pontes metálicas com cálcio, ferro ou alumínio, ou dois destes metais simultaneamente. A justificativa para a eficiência deste produto é que a formação de complexos fósforo-metal-ácidos orgânicos diminui a fixação de fósforo no solo, incrementando assim o aproveitamento do fertilizante fosfatado pelas culturas. Para verificar estes efeitos realizou-se experimento em casa de vegetação e campo, respectivamente intitulados: (i) \"Frações de fósforo no solo mediante a aplicação de superfosfato orgânicocomplexado\" e \"(ii) Uso do superfosfato orgânico-complexado na cultura da cana-de-açúcar\". O objetivo geral do trabalho foi avaliar o efeito da aplicação do SOC na adsorção de fósforo em solos com textura contrastantes submetidos ou não, a correção de acidez e na nutrição da cultura da cana-de-açúcar. No experimento em casa de vegetação verificou-se em solo arenoso e argiloso, com e sem correção de acidez, o efeito da aplicação dos fertilizantes orgânico-complexados nas frações de fósforo do solo através do fracionamento proposto por Hedley. No solo arenoso a maior parte do fósforo aplicado via fertilizante permanece nas frações inorgânicas lábeis as quais tem aumento em função da aplicação do superfosfato orgânico-complexado, além do efeito sinérgico deste com a prática da calagem. No solo argiloso a aplicação do SOC aumenta as formas de fósforo orgânico lábil no solo, além, pela interação sinérgica com a correção da acidez, de diminuir a quantidade de fósforo inorgânico quimiossorvido a ferro e alumínio. O experimento em campo avaliou os efeitos da aplicação de superfosfato orgânico-complexado (SOC) e superfosfato simples (SFS), nas doses de 0, 45, 90, 135 e 180 kg ha-1 de P2O5 em cana planta, além da reaplicação da dose 45 kg ha-1 de P2O5 na soqueira, apenas nos tratamentos que anteriormente receberam 45 e 90 kg ha-1. Em cana planta a aplicação do SFS aumenta a massa de matéria seca de colmo devido a aplicação de níveis crescentes de P2O5, enquanto o uso do SOC não apresentou nenhuma influência, além de promover menor acúmulo de fósforo nesta parte da planta. Na soqueira, a produtividade de colmos industrializáveis e o acúmulo de massa seca no colmo não tem efeito da aplicação dos fertilizantes, porém há menor acúmulo de matéria seca, nitrogênio e fósforo no ponteiro com o uso do fertilizante orgânico-complexado. / In weathered tropical soils there is high phosphorus adsorption, turning the nutrient less available. The main strategy for increasing the levels of phosphorus in the soil is through phosphate fertilization, however 80% of the total nutrient applied to the soil becomes unavailable. The addition of organic matter is important in reducing the phosphorus adsorption due to the formation of humic substances which block the adsorption sites in addition to acting on the insoluble phosphate salts. However, for these beneficial effects there is a need of adding quite large amounts of organic compounds which would result in economical and logistic problems to the producers. Trying to solve this problem the organiccomplexed superphosphate (OCS), which have in their composition the presence of organic chelators (humic acids) complexed with monocalcium phosphate through metal bonds with calcium, iron or aluminum, or two of these metals simultaneously. The reason for the efficiency of this product is that the formation of the complex phosphorus-metal-organic acids inhibits the fixation of phosphorus in the soil, thereby increasing the use of phosphate fertilizer by crops. To verify these effects, it was performed an experiment in the greenhouse and field, respectively entitled: (i) \"Phosphorus fractions in soil by application of organiccomplexed superphosphate\" and \"(ii) organic-complexed superphosphate in the culture of cane sugarcane \". The overall objective was to evaluate the effect of the application of OCS in phosphorus adsorption in soils with contrasting textures submitted or not to the correction of acidity and also in the nutrition of cane sugar. In the greenhouse experiment, it was verified in sandy and loamy soil, with and without correction of acidity, the effect of application of organic-complexed fertilizers on soil phosphorus fractions by fractionation proposed by Hedley. In the sandy soil most of the phosphorus applied via fertilizer remained in the labile organic fractions which increase due to the application of the organic super-complexed phosphate, in addition to the synergistic effect to the practice of lime. In clay soil the application of OCS increased the forms of labile organic phosphorus in the soil, besides its synergistic interaction with the soil acidity decreasing the amount of inorganic phosphorus chemically fixed on iron and aluminum. The field experiment evaluated the effects of organic-complexed superphosphate (OCS) and simple superphosphate (SS) applications at doses of 0, 45, 90, 135 and 180 kg ha-1 of P2O5 in plant cane, but the reapplication of the 45 kg ha-1 of P2O5 dose on ratoon was only in treatments that previously received 45 and 90 kg ha-1. In plant cane the application of SFS increased stalk dry matter due to the application of crescent levels of P2O5, while the use of OCS had no influence, in addition to promoting lower phosphorus accumulation in this part of the plant. In the ratoon, the productivity of industrialized stalks and dry matter accumulation in the stem had no effect through fertilizer application, but there were lower accumulation of dry matter, nitrogen and phosphorus matter in the growing point with the use of organic-complexed fertilizer.

An injection technique, in which undisturbed soil cores are labelled with ³²P to study dissolution of phosphate fertilisers in the soil, was evaluated in field and glasshouse trials. When ³²P was injected between 0-150 mm depths of the undisturbed soil columns and fertilisers applied at the surface, the amounts of fertiliser P dissolved, as measured by the increases in the exchangeable P pools, were overestimated. Three possible reasons were suggested: (i) the interaction between surface-applied fertiliser, ³²P injected through the whole soil column, and the vertical decline in root density, (ii) the decline of specific activity in the exchangeable P pool due to losses of ³²P to nonexchangeable P pools and continuous addition of P from fertiliser dissolution, and (iii) non-uniform distribution of ³²P vis-a-vis ³¹P phosphate. The injection technique may be employed to assess the effectiveness of phosphate fertilisers by introducing a concept, the fertiliser equivalent (FE). The FE is a measure of the amounts of soil exchangeable P that the fertilisers are equivalent to in supplying P to plants, when applied at the specific location. Soluble single superphosphate (SSP) applied at the surface of undisturbed grassland soil cores (Tekapo fine sandy loam), was much more effective than surface-applied unground North Carolina phosphate rock (NCPR) and 30% acidulated NCPR with phosphoric acid (NCPAPR) within the 56 day period of plant growth. An isotopic dilution method, based on tracer kinetic theory, was developed to study the rates of dissolution (F in) and retention (F out) of phosphate fertilisers in the soil in growth chamber experiments. The estimation of F in and F out required labelling of the soils with carrier-free ³²P and determination of the corresponding values of the specific activities of the exchangeable P pools, SA₁ and SA₂, and the sizes of the exchangeable P pools, Q₁ and Q₂, at times t₁ and t₂. Most of the phosphate in the monocalcium phosphate (MCP) solution entered the exchangeable P pool immediately after addition to the soils (Tekapo fine sandy loam and Craigieburn silt loam), and there was little further phosphate input. With increasing periods of incubation, the phosphate was quickly transformed to less rapidly exchangeable forms. In the soils treated with ground North Carolina phosphate rock (<150 µm, NCPR) or partially acidulated (30%) NCPR with phosphoric acid (NCPAPR), the initial exchangeable P pools were not as large as those in the soils treated with MCP, but were maintained at relatively stable concentrations for extended periods, due to the continuous dissolution of PR materials and to lower rates of pretention. An increase in P-retention caused a slight rise in the rate of PR dissolution, but also a rise in the rate of P-retention by the soil. The rate of dissolution was higher at a lower application rate in relative terms, but smaller in absolute terms. The trends in the changes of plant-available P in the soils, measured by the water extractable P, Bray I P and Olsen P, correspond to those predicted by the F in and F out values. The average rates of dissolution between 1-50 and 50-111 days estimated by the F in, however, were higher than those estimated by extractions with 0.5 M NaOH followed by 1 M HCl, and with 0.5 M BaCl₂/TEA. This is partly because the Fin values reflect a plant growth effect on PR dissolution. The relative agronomic effectiveness of NCPR and NCPAPR with respect to MCP was higher after 50 and 111 days of incubation than after 1 day. The F in values were included in all the two-variable models constructed by stepwise regression to describe the relationship between plant P uptake and soil measurements. The amounts of variation in plant P uptake accounted for by the regression model was significantly improved by including F in in the model. This indicates the importance of fertiliser dissolution rates in affecting soil P supply, when phosphate fertilisers differing in solubility are applied.

Soil P fractionation was used to examine changes in soil inorganic and organic P under grazed irrigated pasture in a long-term field trial at Winchmore in Mid-Canterbury. The soil P fractionation scheme used involved sequential extractions of soil with O.5M NaHCO₃ @ pH 8.5 (NaHCO₃ P), 0.1M NaOH (NaOH I P), 1M HCl (HCl P) and 0.1M NaOH (NaOH II P). The Winchmore trial comprised 5 treatments: control (no P since 1952), 376R (376 kg superphosphate ha⁻¹ yr⁻¹ 1952-1957, none since), 564R (564 kg superphosphate ha⁻¹ yr⁻¹ 1952-1957, none since) 188PA (188 kg superphosphate ha⁻¹ yr⁻¹ since 1952) and 376PA (376 kg superphosphate ha⁻¹ yr⁻¹ since 1952: Topsoil (0-7.5cm) samples taken from the different treatments in 1958, 1961, 1965, 1968, 1971, 1974 and 1977 were used in this study. Changes in soil P with time showed that significant increases in soil inorganic P occurred in the annually fertilised treatments (l88PA, 376PA). As expected, the overall increase in total soil inorganic P between 1958 and 1977 was greater in the 376PA treatment (159 µg P g⁻¹) than that in the 188PA treatment (37 µg P g⁻¹). However, the chemical forms of inorganic P which accumulated in the annually fertilised treatments changed with time. Between 1958 and 1971 most of the increases in soil inorganic P in these treatments occurred in the NaHCO₃ and NaOH I P fractions. On the other hand, increases in soil inorganic P in the annually fertilised treatments between 1971 and 1977 were found mainly in the HCl and NaOH II P fractions. These changes in soil P forms were attributed to the combined effects of lime addition in 1972 and increased amounts of sparingly soluble apatite P and iron-aluminium P in the single superphosphate applied during the 1970's. In the residual fertiliser treatments (376R, 564R) significant decreases in all of the soil inorganic P fractions (i.e. NaHCO₃ P, NaOH I P, HCl P, NaOH II p) occurred between 1958 and 1977 following the cessation of P fertiliser inputs in 1957. This was attributed to continued plant uptake of P accumulated in the soil from earlier P fertiliser additions. However, levels of inorganic P in the different soil P fractions in the residual fertiliser treatments did not decline to those in the control which indicated that some of the inorganic P accumulated in the soil from P fertiliser applied between 1952 and 1957 was present in very stable forms. In all treatments, significant increases in soil organic P occurred between 1958 and 1971. The overall increases in total soil organic P were greater in the annually fertilised treatments (70-86 µg P g⁻¹) than those in the residual fertiliser (55-64 µg P g⁻¹) and control (34 µg P g⁻¹) treatments which reflected the respective levels of pasture production in the different treatments. These increases in soil organic P were attributed to the biological conversion of native and fertiliser inorganic P to organic P in the soil via plant, animal and microbial residues. The results also showed that annual rates of soil organic P accumulation between 1958 and 1971 decreased with time which indicated that steady-state conditions with regard to net 'organic P accumulation were being reached. In the residual fertiliser treatments, soil organic P continued to increase between 1958 and 1971 while levels of soil inorganic P and pasture production declined. This indicated that organic P which accumulated in soil from P fertiliser additions was more stable and less available to plants than inorganic forms of soil P. Between 1971 and 1974 small (10-38 µg P g⁻¹) but significant decreases in total soil organic P occurred in all treatments. This was attributed to increased mineralisation of soil organic P as a result of lime (4 t ha⁻¹) applied to the trial in 1972 and also to the observed cessation of further net soil organic P accumulation after 1971. Liming also appeared to affect the chemical nature of soil organic P as shown by the large decreases in NaOH I organic P(78-88 µg P g⁻¹) and concomitant smaller increases in NaOH II organic P (53-65 µg P g⁻¹) which occurred in all treatments between 1971 and 1974. The chemical nature of soil organic P in the Winchmore long-term trial was also investigated using 31p nuclear magnetic resonance (NMR) spectroscopy and gel filtration chromatography. This involved quantitative extraction of organic P from the soil by sequential extraction with 0.1M NaOH, 0.2M aqueous acetylacetone (pH 8.3) and 0.5M NaOH following which the extracts were concentrated by ultrafiltration. Soils (0-7.5cm) taken from the control and 376PA annually fertilised treatments in 1958, 1971 and 1983 were used in this study. 31p NMR analysis showed that most (88-94%) of the organic P in the Winchmore soils was present as orthophosphate monoester P while the remainder was found as orthophosphate diester and pyrophosphate P. Orthophosphate monoester P also made up almost all of the soil organic P which accumulated in the 376PA treatment between 1958 and 1971. This indicated that soil organic P in the 376PA and control treatments was very stable. The gel filtration studies using Sephadex G-100 showed that most (61-83%) of the soil organic P in the control and 376PA treatments was present in the low molecular weight forms (<100,000 MW), although the proportion of soil organic P in high molecular weight forms (>100,000 MW) increased from 17-19% in 1958 to 38-39% in 1983. The latter was attributed to the microbial humification of organic P and indicated a shift toward more complex and possibly more stable forms of organic P in the soil with time. Assuming that the difference in soil organic P between the control and 376PA soils sampled in 1971 and 1983 represented the organic P derived from P fertiliser additions, results showed that this soil organic P was evenly distributed between the high and low molecular weight fractions. An exhaustive pot trial was used to examine the relative availability to plants of different forms of soil inorganic and organic P in long-term fertilised pasture soils. This involved growing 3 successive crops of perennial ryegrass (Lolium perenne) in 3 Lismore silt loam (Udic Ustochrept) soils which had received different amounts of P fertiliser for many years. Two of the soils were taken from the annually fertilised treatments in the Winchmore long term trial (188PA, 376PA) and the third (Fairton) was taken from a pasture which had been irrigated with meatworks effluent for over 80 years (65 kg P ha⁻¹ yr⁻¹). Each soil was subjected to 3 treatments, namely control (no nutrients added), N100 and N200. The latter treatments involved adding complete nutrient solutions with different quantities of N at rates of 100kg N ha⁻¹ (N100) and 200kg N ha⁻¹ (N200) on an area basis. The soil P fractionation scheme used was the same as that used in the Winchmore long-term trial study (i.e. NaHCO₃ P, NaOH I P, HCl P, NaOH II p). Results obtained showed that the availability to plants of different extracted inorganic P fractions, as measured by decreases in P fractions before and after 3 successive crops, followed the order: NaHCO₃ P > NaOH I P > HCl P = NaOH II P. Overall decreases in the NaHCO₃ and NaOH I inorganic P fractions were 34% and 16% respectively, while corresponding decreases in the HCl and NaOH II inorganic P fractions were small «10%) and not significant. However, a significant decrease in HCl P (16%) was observed in one soil (Fairton-N200 treatment) which was attributed to the significant decrease in soil pH (from 6.2 to 5.1) which occurred after successive cropping. Successive cropping had little or no effect on the levels of P in the different soil organic P fractions. This indicated that net soil organic P mineralisation did not contribute significantly to plant P uptake over the short-term. A short-term field experiment was also conducted to examine the effects of different soil management practices on the availability of different forms of P to plants in the long-term fertilised pasture soils. The trial was sited on selected plots of the existing annually fertilised treatments in the Winchmore long-term trial (188PA, 376PA) and comprised 5 treatments: control, 2 rates of lime (2 and 4 t ha⁻¹ ) , urea fertiliser (400kg N ha⁻¹ ) and mechanical cultivation. The above ground herbage in the uncultivated treatments was harvested on 11 occasions over a 2 year period and at each harvest topsoil (0-7.5 cm) samples were taken from all of the treatments for P analysis. The soil P fractionation scheme used in this particular trial involved sequential extractions with 0.5M NaHCO₃ @ pH 8.5 (NaHCO₃ P), 0.1M NaOH (NaOH P), ultrasonification with 0.1M NaOH (sonicate-NaOH p) and 1M HCl (HCl P). In addition, amounts of microbial P in the soils were determined. The results showed that liming resulted in small (10-21 µg P g⁻¹) though significant decreases in the NaOH soil organic P fraction in the 188PA and 376PA plots. Levels of soil microbial P were also found to be greater in the limed treatments compared with those in the controls. These results indicated that liming increased the microbial mineralisation of soil organic P in the Winchmore soils. However, pasture dry matter yields and P uptake were not significantly affected. Although urea significantly increased dry matter yields and P uptake, it did not appear to significantly affect amounts of P in the different soil P fractions. Mechanical cultivation and the subsequent fallow period (18 months) resulted in significant increases in amounts of P in the NaHCO₃ and NaOH inorganic P fractions. This was attributed to P released from the microbial decomposition of plant residues, although the absence of plants significantly reduced levels of microbial P in the cultivated soils. Practical implications of the results obtained in the present study were presented and discussed.