Variabilidade espacial da suscetibilidade magnética para definição de áreas mínimas de manejo de fósforo adsorvido
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Data
2020-07-27
Autores
Silva, Luis Fernando Vieira da
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Universidade Estadual Paulista (Unesp)
Resumo
O fósforo (P) é um macronutriente não renovável, fundamental para o desenvolvimento e incremento produtivo das lavouras. Portanto, sua dinâmica e interações com óxidos de ferro podem ser úteis na definição estratégica de áreas mínimas de aplicação de P. Técnicas de sensoriamento do solo como suscetibilidade magnética (χ) permitem a identificação e quantificação de minerais ferrimagnéticos como magnetita e maghemita. Logo, a χ pode ser um atributo estratégico para mapear fósforo adsorvido em solos com baixo e alto teor de óxidos de ferro. O objetivo neste trabalho foi avaliar a variabilidade espacial dos minerais magnéticos e o potencial da χ no reconhecimento de áreas mínimas de P ads em solos sob contraste litológico com ampla variação mineralógica. Em uma área de 443 hectares cultivada com cana-de-açúcar no estado de São Paulo foram coletadas 83 amostras de solo na profundidade de 0,00 – 0,20 m. A análise de suscetibilidade magnética em baixa e alta (χ Lf) frequência (χ hf) foi realizada em todas as amostras de solo. A caraterização dos minerais magnéticos foi realizada por difração de raios X (DRX) e a diferenciação química dos minerais magnéticos litogênico (magnetita-Mt) e pedogênico (maghemita-Mh) foram determinados por χ antes e depois de redução química por citrato-bicarbonato-dithionito (DBC), em seguida determinou-se o fósforo adsorvido. Os resultados analíticos foram avaliados por análises descritivas e o padrão espacial por aplicação de técnica geoestatística. A χLf diferencia solos do seu respectivo material de origem mesmo em condição de intemperismo elevado e complexidade litológica. Regressão lineares positivas entre P ads e argila (R2 = 0,78), P ads e χLf (R2 = 0,86) e P ads e Mh (R2 = 0,84) assinalam o uso da χLf como componente de funções de pedotransferência para quantificação indireta do Pads no solo. A quantificação de Mh e Mt por χLf mostra-se mais sensível do que a DRX. Esta técnica indicou que a Mh é o principal mineral condicionador do sinal magnético do solo. O padrão espacial dos minerais magnéticos indica que Mh é herdada da oxidação direta da Mt. A χLf do solo é sensível à variabilidade espacial do P ads, podendo auxiliar na identificação de áreas mínimas de adubação fosfatada em solos sob complexos litológicos.
– Phosphorus (P) is a non-renewable macronutrient, essential for the development and productive increase os crops. Therefore, its dynamics and interactions with iron oxides can be useful in the strategic definition of minimum areas of application of P. Soil sensing techniques as magnetic susceptibility (χ) allow the magnetite and maghemite. Therefore, χ can be a strategic attribute for mapping phosphorus adsorbed in soild with low and high iron oxide content. The objective of this work was to evaluate the spatial variability of magnetic minerals and the potential of χ in the recognition of minimal areas of P ads in soils under lithological contrast with wide mineralogical variation. In an area of 443 hectares cultivated with sugar cane in the State of São Paulo, 83 samples of soil with a depth of 0,00 – 0,20 m were collected. An analysis of magnetic susceptibility (χ) at low and high (χLf) frequency (χHf) was performed on all samples as soil. The chemical characterization of magnetic minerals was carried out by X-ray diffraction (XRD) and the chemical distinction of lithogenic magnetic minerals (magnetite-Mt) and pedogenesis (maghemite-Mh) citratebicarbonate-dithionite (CBD), then determined or adsorbed phosphorus. The analytical results were applied by descriptive analysis and the spatial pattern by application of geostatistical techniques. ΧLf differentiates environments from its parent material even under highly weathered solution conditions and lithological complexity. Positive linear regressions between P ads and clay (R2 = 0,78), Pads and χLf (R2 = 0,86) and Pads and Mh (R2 = 0,84) indicate the use of χLf as a component of pedotransfer functions for indirect quantification of P ads in the soil. The quantification of Mh and Mt by χLf is more sensitive than XRD. This technique indicated that Mh is the main mineral conditioning the soil magnetic signal. The spatial pattern of magnetic minerals indicates that Mh is inherited from the direct oxidation of Mt. The χLf of the soil is sensitive to thee spatial variability of P ads, and may assist in the identification of minimal areas of phosphate fertilization in soils under lithological complexes.
– Phosphorus (P) is a non-renewable macronutrient, essential for the development and productive increase os crops. Therefore, its dynamics and interactions with iron oxides can be useful in the strategic definition of minimum areas of application of P. Soil sensing techniques as magnetic susceptibility (χ) allow the magnetite and maghemite. Therefore, χ can be a strategic attribute for mapping phosphorus adsorbed in soild with low and high iron oxide content. The objective of this work was to evaluate the spatial variability of magnetic minerals and the potential of χ in the recognition of minimal areas of P ads in soils under lithological contrast with wide mineralogical variation. In an area of 443 hectares cultivated with sugar cane in the State of São Paulo, 83 samples of soil with a depth of 0,00 – 0,20 m were collected. An analysis of magnetic susceptibility (χ) at low and high (χLf) frequency (χHf) was performed on all samples as soil. The chemical characterization of magnetic minerals was carried out by X-ray diffraction (XRD) and the chemical distinction of lithogenic magnetic minerals (magnetite-Mt) and pedogenesis (maghemite-Mh) citratebicarbonate-dithionite (CBD), then determined or adsorbed phosphorus. The analytical results were applied by descriptive analysis and the spatial pattern by application of geostatistical techniques. ΧLf differentiates environments from its parent material even under highly weathered solution conditions and lithological complexity. Positive linear regressions between P ads and clay (R2 = 0,78), Pads and χLf (R2 = 0,86) and Pads and Mh (R2 = 0,84) indicate the use of χLf as a component of pedotransfer functions for indirect quantification of P ads in the soil. The quantification of Mh and Mt by χLf is more sensitive than XRD. This technique indicated that Mh is the main mineral conditioning the soil magnetic signal. The spatial pattern of magnetic minerals indicates that Mh is inherited from the direct oxidation of Mt. The χLf of the soil is sensitive to thee spatial variability of P ads, and may assist in the identification of minimal areas of phosphate fertilization in soils under lithological complexes.
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Palavras-chave
Óxido de ferro, magnetita, maghemita, adsorção de P, pedometria