Abstract
Previous observations have shown that the concentration of root distribution in the upper layers of the Cerrado soils was not due to the existence of a low pH and high aluminum toxicity, as previously reported, but to the lack of phosphorus or calcium in the deep layers that remained unimproved.
To evaluate the effect of phosphorus and lime on the root distribution in the deep layers, experiments were carried out in fields of two typical Cerrado soils, Helvic Ferralsols and Rhodic Ferralsols. The soil layer was divided into two parts, 0-15 and 15-30 cm depth from the soil surface. Phosphorus and lime were applied, together or separately, to the deeper layers. Better penetration of tap-roots and distribution of roots in the deeper layers of the soils were observed in the plots where both phosphorus and lime had been applied in the deeper layers. A similar tendency was also observed in the plots with deep incorporation of phosphorusonly, in spite of the fact that the pH and percentage of aluminum saturation of the plots were 4.8 and 57, respectively, which correspond to a comparatively high level of acidity and aluminum toxicity. A slight improvement of the root distribution in the deep layers of the soils was observed in the plots subjected to deep incorporation of lime only.
On the basis of results obtained, it can be concluded that the concentration of soybean roots in the upper layers of cerrado soils is not due to high aluminum toxicity associated with the low pH of the soils, but that it can be ascribed to the difference in phosphorus and calcium contents between the upper and deeper layers of the soils since fertilizers are applied each year in the former whereas the latter remain unimproved. Such abnormal root distribution can be improved by deep incorporation of phosphorus and lime.
