Uso de resíduos vegetais em solos ácidos sob sistema de plantio direto

AUTOR(ES)
DATA DE PUBLICAÇÃO

2007

RESUMO

The Brazilian soils are characterized by low natural fertility, where the main chemical limitations are high acidity and low basic exchangeable cation saturation that can affect the majority of cash crop productions. Liming is the principal practice to reduce soil acidity and to increase basic cations in these soils with high pH-dependent cation exchangeable capacity (CEC). Under no tillage system, liming is applied on the soil surface without mechanical incorporation in the soil profile, which chemical effects have been limited to the local of application. The correction of subsoil acidity depends on the time, the lime rates and the metal organic complexes formed by organic anions released from organic residues with Ca and Mg, increasing their mobility?s in the soil profile and the neutralization of free toxic Al3+. The objective of this study was to evaluate the effects of winter cover crops on the superficial lime reaction and the chemical changes in the soil profile. Laboratory and field experiments were conducted in the headquarters of the Instituto Agronômico do Paraná, IAPAR, at Londrina, Brazil. Under laboratory conditions, soil columns were filled up with samples of a dystropheric red latosol (Oxisol) with and without superficial lime application. Then, plant extract of soybean, corn, wheat, black oats and radish were applied on the soil surface. Under field condition, micro-plots with a dystrophic red latosol were superficially limed and cultivated with the following winter cover crops: wheat, radish-black outs rotations and mixtures of radish+black outs. An addition treatment was included with bare soil. In the summer time, all treatments were conducted with soybean-corn rotation. Laboratory experiments showed that plant extracts associated with superficial lime application increased pH, Ca, Mg, K and basic cation saturation from the superficial to the sub superficial soil profile. Lime without plant extract showed effects in the upper superficial soil layer only. Without lime treatment, plant extract showed chemical effects down to the sub soil surface. Radish was the best plant extract for changing soil chemical properties under both liming and no liming treatments. Under field conditions, the results showed that all soil winter cover crops improved soil chemical characteristics from the superficial to 40 cm depth soil layers. The mixture radish+black outs showed the most pronounced effects on pH, potential acidity and basic cation saturation. However, these effects decreased after 24 months of superficial lime application. The winter cover crops also improved the soybean and corn grain yields in the summer. The best results were observed for wheat and radish+black outs mixture treatments. Water soluble organic molecules present in the plant extracts were suggested to be responsible, in part, for the chemical changes in the soil profile in both experiments. The soil plant covers showed to be beneficial for speeding up lime reactions in acid soils and improving soil chemical characteristics by releasing soluble organic compounds.

ASSUNTO(S)

liming of soils. cobertura morta. soil mulching calagem dos solos cultivos de cobertura solos - acidez

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