The effectiveness of surface application of lime to soils under a no‐till (NT) system, particularly with regard to subsoil acidity, is uncertain, and long‐term data is needed to determine optimum surface liming rates in this cropping system. A field experiment was performed in the period from 1993 through 2003 in Paraná State, Brazil, on a loamy, kaolinitic, thermic Typic Hapludox to evaluate the extent of the downward movement of surface‐applied lime in a NT system, and the effect on grain yields under crop rotation. The treatments consisted of dolomitic limestone at the rates of 0, 2, 4, and 6 t ha−1, calculated to raise the base saturation in the topsoil (0–20 cm) to 50, 70, and 90%. Surface‐applied lime under NT was effective in alleviating soil acidity below the point of placement, and increased the cumulative grain yield of the crops. The effects of surface liming on all three acidity‐related variables (pH, Al, and basic cations) were significant at 0‐ to 5‐ and 5‐ to 10‐cm depths from 1 yr onward, and also at the 10‐ to 20‐cm depth from 2.5 yr onward, remaining consistent for a period of up to 10 yr after liming. The maximum economic yield was obtained at 4 t ha−1 of limestone, showing that the lime rate estimated by the soil base saturation method at 70% in the 0‐ to 20‐cm depth was appropriate for surface liming recommendation in a NT system.

RESUMOOs resíduos de plantas de cobertura podem mobilizar cátions no solo e beneficiar a ação da calagem superficial, por meio da liberação de ácidos orgânicos de baixo peso molecular da fração solúvel dos resíduos. Entretanto, faltam estudos no campo que comprovem tais efeitos em sistema plantio direto. Para avaliar as alterações químicas do solo e a resposta do milho e da soja com a aplicação de doses de calcário dolomítico na superfície (0,0, 2,5, 5,0 e 7,5 t ha -1 ), na ausência e na presença de cobertura de aveia preta, foi realizado um experimento em um Latossolo Vermelho distrófico textura argilo-arenosa, há cinco anos no sistema plantio direto, em Ponta Grossa (PR) .

No abstract

Aluminum toxicity is one of the major soil factors limiting root growth in acidic soils. Because of the increase in organic matter content in the upper few centimeters of soils under no‐till systems (NTS), most Al in soil solution may be complexed to dissolved organic C (DOC), thus decreasing its bioavailability. The aim of this study was to evaluate the effects of surface liming on Al speciation in soil solution in Brazilian sites under NTS. Field experiments were performed in two regions with contrasting climates and levels of soil acidity: Rondonopolis, Mato Grosso State, on a Rhodic Haplustox, and Ponta Grossa, Paraná State, on a Typic Hapludox. The treatments consisted of a control and three lime rates, surface applied to raise the base saturation to 50, 70, and 90%. Soil solution was obtained at soil water equilibrium (1:1 w/w soil/water ratio). The effects of surface liming on soil chemical attributes and on the composition of the soil solution were dependent on weather conditions, time under NTS, and soil weathering. Most Al in soil solution was complexed to DOC, representing about 70 to 80% of the total Al at pH <5.0, and about 30 to 40% at pH >5.0. Under pH 5.5, the results were closely correlated with the solubility line for amorphous Al. Organic complexes may control Al3+ release into soil solution at pH <5.5. Results suggest that in areas under NTS for a long period of time, Al toxicity might decrease due to its complexation to high‐molecular‐weight organic compounds.

matéria orgânica foi estudada após extração com CuCl 2 0,5 mol L-1 , e por queima da MO por mufla, peróxido de hidrogênio e hipoclorito de sódio. A maior parte do Al na solução dos solos sob SPD estava ligada aos ânions orgânicos (Al-COD), sendo esta forma não tóxica às plantas. Nos valores de pH menores que 5,0 o Al-COD representou cerca de 70 a 80% do Al total na solução, e cerca de 30 a 40% nos valores de pH superiores a 5,0. Cerca de 75 a 80% do Al-COD estava ligado aos ânions de alta massa molecular na solução do solo. No Latossolo Vermelho distrófico (LVd) de Rondonópolis/MT, em que o pH e o teor de alumínio eram baixos, 96% do Al estava complexado com a MO, enquanto no LVd de Ponta Grossa/PR esse valor foi de 75%. O LVd de Rondonópolis/MT, em que o teor de Al extraído por CuCl 2 (complexado pela MO) foi maior, apresentou o maior grau de humificação dos três locais, seguido do Nitossolo Vermelho distroférrico (NVdf) de Botucatu/SP e do LVd de Ponta Grossa/PR. Não houve resposta da soja e do arroz à calagem, nos três locais, nos dois anos agrícolas