Rotation soybean-forage and the contribution of non- exchangeable k in plant nutrition in a cerrado soil
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Data
2019-09-17
Autores
Volf, Marcelo Raphael [UNESP]
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Universidade Estadual Paulista (Unesp)
Resumo
As frações solúveis e trocáveis do K, podem não ser as únicas disponíveis para as plantas, uma vez que a fração não trocável também pode ser utilizada. As plantas de cobertura são eficientes na reciclagem deste nutriente e podem absorver tanto as formas trocáveis como as não trocáveis do K. Portanto, o objetivo deste estudo é identificar a localização do K não-trocável nas frações argila e silte após exaustão causada por sucessivos cultivos de milho, soja ou braquiária ruziziensis (Urochloa ruziziensis), e verificar a eficiência em suprir a demanda de K a partir do K não trocável. O estudo envolveu dois experimentos: 1) Cultivo de soja, milho ou capim- braquiária em vasos por três ciclos sucessivos em solos com alta concentração de K não-trocável, com e sem adubação potássica. As plantas foram removidas dos vasos no momento do pico de acúmulo de K para determinar o K trocável e não-trocável nas plantas e a mineralogia do solo. 2) Um experimento de campo foi realizado envolvendo três sistemas de produção: cultivo de soja com o solo deixado em pousio na entresafra; soja com U. ruziziensis entre culturas; e rotação com U. ruziziensis, com plantio de soja após crescimento da forrageira por 30 meses. O comportamento do K não-trocável foi analisado medindo-se o balanço entre K no solo e nas plantas de cobertura e analisando-se a composição mineralógica do solo. Determinou-se a eficiência das plantas de cobertura, em sucessão ou rotação, sobre a transformação não trocável em K trocável e a capacidade dessas plantas em atuar como biofertilizante para a soja, proporcionando fornecimento de potássio. Para a determinação da mineralogia do solo foi feita a separação das frações areia, silte e argila. Por meio da difração de raios-X foram identificados, em cada fração, quais minerais estavam presentes. Os minerais contidos na argila foram quantificados com a associação das técnicas de difração de raios-X, análise semiquantitativa de acordo com a área de pico de cada mineral e análises térmicas, quantitativas por meio de perda de peso dos minerais devido à temperatura, utilizando caulinita nativa determinada por métodos térmicos como padrão interno. A partir disso, foi possível medir cada mineral contido na argila e a mudança destes devido aos tratamentos. A rotação de culturas é um sistema de produção que proporciona maior disponibilidade de potássio para plantas de soja, bem como melhora a eficiência no uso de fertilizantes K. As plantas Ruzigrass têm maior capacidade de absorver K não-trocável do que soja e milho, embora a soja também use este K, ambas as culturas promovem mudanças na quantidade de vermiculita. O uso de forragem e soja em solo tropical, sem aplicação de K, é um dos agentes de intemperismo dos minerais potássicos presentes neste solo. Sistema e a exaustão de K devido a sucessivas culturas interferem na capacidade tampão de K deste solo a qual é coordenado pela adsorção de K na fração trocável e liberação pela fração não-trocável.
Some plants can utilize the non-exchangeable fraction of K and thus are not limited to the soluble and exchangeable fractions. In particular, cover plants are very efficient in recycling K and can absorb both the exchangeable and non-exchangeable forms. In the present study, the location of non-exchangeable K in the clay and silt fractions of a tropical soil after depletion by successive cropping with maize, soybean or ruzigrass (Urochloa ruziziensis) was identified, and the efficiency of non-exchangeable K in supplying the demand of these plants in soils with high concentrations of non- exchangeable K was determined in soybean-grass crop systems with succession or rotation. The study involved two experiments. In the first experiment, soybean, maize or ruzigrass was cultivated in pots for three successive cycles in soils with a high concentration of non-exchangeable K with and without potassium fertilization. The plants were removed from the pots at the moment of peak accumulation of K to determine the exchangeable and non-exchangeable K in the plants and the soil mineralogy. Second, a field experiment involving three production systems was carried out: soybean cultivation with fallow soil between crops; soybean with U. ruziziensis in the off-season; and rotation of U. ruziziensis with soybean planting after growth of the grass for 30 months. The behavior of non-exchangeable K was analyzed by measuring the balance between K in the soil and in the cover plants and by analyzing the soil mineralogical composition. The efficiency of the cover plants, in succession or rotation, in transforming non-exchangeable to exchangeable K and the ability of these plants to act as a bio-fertilizer for soybean by providing potassium nourishment were determined. For mineralogical analyses, the soil was separated into the sand, silt and clay fractions, and the minerals present in each fraction were identified by X-ray diffraction. The minerals present in the clay fraction were quantified by employing a combination of X-ray diffraction techniques, semiquantitative analysis of the peak area of each mineral, and thermogravimetric analyses using native kaolinite an internal standard. These analyses revealed the effects of each treatment on the content of each mineral in the clay fraction. The results showed that crop rotation improves K availability for soybean plants and the efficiency of K fertilizer utilization. Ruzigrass has a greater ability to absorb non-exchangeable K than soybean and maize, but both ruzigrass and soybean promote changes in the amount of vermiculite. The cultivation of forage grasses and soybean in tropical soil without application of K represents a weathering agent for the minerals present in this soil. Moreover, this cropping system and K exhaustion due to successive cultivation reduce the buffer capacity of K in this soil, which is regulated by the adsorption of K in the exchangeable fraction and release by the non-exchangeable fraction.
Some plants can utilize the non-exchangeable fraction of K and thus are not limited to the soluble and exchangeable fractions. In particular, cover plants are very efficient in recycling K and can absorb both the exchangeable and non-exchangeable forms. In the present study, the location of non-exchangeable K in the clay and silt fractions of a tropical soil after depletion by successive cropping with maize, soybean or ruzigrass (Urochloa ruziziensis) was identified, and the efficiency of non-exchangeable K in supplying the demand of these plants in soils with high concentrations of non- exchangeable K was determined in soybean-grass crop systems with succession or rotation. The study involved two experiments. In the first experiment, soybean, maize or ruzigrass was cultivated in pots for three successive cycles in soils with a high concentration of non-exchangeable K with and without potassium fertilization. The plants were removed from the pots at the moment of peak accumulation of K to determine the exchangeable and non-exchangeable K in the plants and the soil mineralogy. Second, a field experiment involving three production systems was carried out: soybean cultivation with fallow soil between crops; soybean with U. ruziziensis in the off-season; and rotation of U. ruziziensis with soybean planting after growth of the grass for 30 months. The behavior of non-exchangeable K was analyzed by measuring the balance between K in the soil and in the cover plants and by analyzing the soil mineralogical composition. The efficiency of the cover plants, in succession or rotation, in transforming non-exchangeable to exchangeable K and the ability of these plants to act as a bio-fertilizer for soybean by providing potassium nourishment were determined. For mineralogical analyses, the soil was separated into the sand, silt and clay fractions, and the minerals present in each fraction were identified by X-ray diffraction. The minerals present in the clay fraction were quantified by employing a combination of X-ray diffraction techniques, semiquantitative analysis of the peak area of each mineral, and thermogravimetric analyses using native kaolinite an internal standard. These analyses revealed the effects of each treatment on the content of each mineral in the clay fraction. The results showed that crop rotation improves K availability for soybean plants and the efficiency of K fertilizer utilization. Ruzigrass has a greater ability to absorb non-exchangeable K than soybean and maize, but both ruzigrass and soybean promote changes in the amount of vermiculite. The cultivation of forage grasses and soybean in tropical soil without application of K represents a weathering agent for the minerals present in this soil. Moreover, this cropping system and K exhaustion due to successive cultivation reduce the buffer capacity of K in this soil, which is regulated by the adsorption of K in the exchangeable fraction and release by the non-exchangeable fraction.
Descrição
Palavras-chave
Non-exchangeable potassium, Exchangeable potassium, Weathering of potassium minerals in tropical soils, Potássio não trocável. potássio trocável, Intemperismo dos minerais potássicos em solos tropicais, Sistemas de produção soja-forrageira, Soybean-forage, Crop system, Potássio não trocável, Potássio trocável