Crescimento e acúmulo de fósforo pela soja cultivada em sucessão a diferentes gramíneas forrageiras adubadas com super fosfato triplo e fosfato reativo de arad

Abstract

RESUMOConduziu-se este trablho, com o objetivo de avaliar o efeito do cultivo prévio de diferentes gramíneas forrageiras, adubadas com superfosfato triplo (SFT) e fosfato reativo de arad (FRA), sobre o crescimento, produção e acúmulo de P pela soja. Foram realizados dois experimentos, um em Cambissolo Háplico tb distrófico típico e o outro em Latossolo Vermelho distrófico típico textura muito argilosa. Para os dois experimentos, o delineamento experimental foi o inteiramente casualizado em esquema fatorial 4 x 2 + 2, sendo o cultivo prévio de quatro gramíneas forrageiras (Brachiaria decumbens Stapf -braquiária, Brachiaria brizantha Hochst Stapf -braquiarão, milheto e sorgo forrageiro) adubadas com duas fontes de P (FRA e SFT) e dois tratamentos adicionais que é o cultivo da soja sem o cultivo prévio de plantas de cobertura e adubadas com SFT e FRA. As plantas foram colhidas após completar o ciclo de desenvolvimento. Foram determinadas a produtividade de grãos (PG) e de massa seca da parte aérea (MSPA) e o acúmulo de fósforo na parte aérea e nos grãos da soja, as forrageiras imobilizaram o P do SFT, reduzindo o efeito residual para a soja e o feijoeiro. Quando as gramíneas forrageiras foram adubadas com o FRA, houve um aumento do efeito residual, com aumento da produtividade da soja em sucessão às plantas de cobertura, com exceção para o cultivo em sucessão ao braquiarão. Termos para indexação: Efeito residual, adubação fosfatada, Glycine max e Phaseolus vulgaris. ABSTRACTThe objective of this study was to evaluate the effect of the previous cultivation of different forage grasses fertilized with triple superphosphate (TSP) and reactive Arad phosphate (RAP) on growth, yield, and accumulation of P by soybean. Two experiments were carried out ; one in Haplic Cambisol typical tb distrophic, medium texture and the other in Red Latosol typical distrophic very clayey texture. For both experiments, the experimental design was a completely randomized one in a 4 x 2 + 2 factorial scheme; the previous crop being of four forage grasses utilized as cover plants in no-tillage system (Brachiaria decumbens Stapf -braquiária, Brachiaria brizantha Hochst Stapf -braquiarão, millet and forage sorghum) fertilized with two sources of P (RAP and TSP) and two additional treatments, which are the cultivation of soybean and bean plant without the previous growing of cover plants, and also fertilized with TSP and RAP. The plants were harvested after they had completed the development cycle. Grain and shoot dry matter yield and P accumulation in the shoot and in the grains of soybean were determined. The forage plants immobilized the P of TSP, reducing the residual effect for soybean. When forage grasses are fertilized with RAP, there is increased residual effect with increasing yield of soybean in succession to the cover plants, with exception for the growing in succession to Brachiaria brizanta.

Ruzigrass affecting soil-phosphorus availability

“…Moreover, some of the undissolved RRP might add to the extracted Ca-P, as evidenced by higher Ca-P in the 0-5 cm soil depth of plots. Similar results were obtained by Rodrigues et al (2009), which observed increases in Ca-P after RRP application. The effect of ruzigrass in reducing Ca-P, in soluble phosphate plots, is likely related to the utilization of this P fraction by the cover crop.…”

Brachiaria as a Cover Crop to Improve Phosphorus Use Efficiency in a No-till Oxisol

“…These data demonstrate that soluble P released by the soluble source was taken up and stored in ruzi grass tissues, and it was not released and mineralized in time to meet the next crop demand, ensuring a better response to the soluble source in the absence of the cover crop. Rodrigues et al (2009) also found that forages such as pearl millet, brachiarias, and sorghum immobilized P from TSP, decreasing its residual effect for soybeans; when grasses were fertilized with NRP, there was an increase in the residual effect, with better P use efficiency by the soybean crop grown following these cover crops.…”

Phosphorus bioavailability in soybean grown after pasture under different fertility regimes

“…Therefore, high levels of available P in soil did not result in a higher P accumulation in the plants when the crop had been directly fertilized with P. This shows that the P applied to the pasture preceding the soybean and available to the plant is used more efficiently than P fertilizer applied at soybean sowing. Rossi et al (1999) evaluated the residual effect of four P levels and four phosphorus sources applied to two pastures (Centrosema pubescens and Brachiaria decumbens) preceding rice cultivation: they also noted the residual effect of P coming from triple superphosphate applied to pasture. Considering the role of the root system of grasses in the solubilization of P by the exudation of organic acids (CORRÊA et al, 2004), Urochloa decumbens may have played a key role in the absorption efficiency of residual P and its subsequent release by mineralization of P held in DM (organic P).…”

“…Another strategy is to apply all or part of the annual crop's fertilization to the preceding crop, which is usually a green manure in non-tilled pasture or crop-livestock systems . Francisco et al (2007) and Rodrigues et al (2009) reported that early P fertilization of wiregrass [Eleusine coracana (L.) Gaertn. ], produced more plant biomass and an accumulation of P which did not affect soybean grain yield.…”