Eficiência agronômica de fosfatos de rocha, utilizados isoladamente ou associados ao superfosfato triplo, para a cultura da soja / Agronomic effectiveness of phosphate rocks, by itself or associated with the triple superphosphate, for soybean

AUTOR(ES)
DATA DE PUBLICAÇÃO

2008

RESUMO

due to a low natural availability of P in cultivated soils. To obtain good economically yield is necessary P fertilizer application. Nearly all phosphorus fertilization is carried out using acidulated phosphate, which have high water solubility and when applied in the soil may increase the P availability at times of low demand by the crop. To associate the use of acidulated phosphate (e.g. Triple Superphosphate - TSP) and phosphate rock (PR), since they are sources of different solubility, can be an alternative to adequately manage fertilizers aiming to reduce the losses of P applied to crops. Two field experiments were carried out, one in Maranhão State (Balsas) and another in the State of São Paulo (Palmital), both aiming to evaluate the agronomic effectiveness of P sources for soybean regarding the method of application and the P source solubility. In both experiments the P sources were applied by itself or in mixtures combining both P fertilizers. The mixed application of the sources was carried out basically in two forms: i: applying the sources separately, but in the same treatment, like broadcasted-PR application and banded-TSP, and ii: applying the mixtures obtained through different proportions of TSP and PR. Like this, the relative agronomic effectiveness (RAE) of P sources was evaluated concerning the localization of the fertilizer and in different conditions of water P solubility. RAE of sources with lower solubility was generally higher when they were applied broadcasted and incorporated into the soil. For example, the RAE of broadcasted-PR was 77% (average of the three harvests), while, the banded-PR resulted in 44% of RAE. The use of PR broadcasted and TSP banded showed to be a feasible agronomic alternative, once besides the high yield results in the first harvest, it made possible a good residual effect for two years, with the residual effect of the PR leading to up to 40% of the final yield values when low rates of P (TSP) was used. When the association of the sources was carried out by granulated mixed components, it was observed that the water solubility necessary to obtain similar soybean yield as TSP was of approximately 60%. The association of the P sources, with the objective to obtain lower levels of solubility, seems to be a feasible alternative to manage phosphorus fertilizers.

ASSUNTO(S)

latossolos aptidão agrícola soja. fosfatos mixture of p sources application method. oxisols soil fertility fertilizantes fosfatados fertilidade do solo p sources solubility glycine max

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