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In a no-till system (NTS) on naturally acidic soils, surface liming is essential to neutralize soil acidity and increases crop productivity. As a result, the soil organic matter (SOM) pools of the soil surface layers may change, reflecting increased C inputs by crop residues. The objective of this study was to quantify changes in SOM pools and the rate of C sequestration that occur in response to surface liming in a long-term NTS experiment. The experiment was conducted in an Oxisol in southern Brazil. The treatments consisted of the application of 0 or 6 Mg ha~^ of dolomitic lime on the soil surface in 1993 and a reapplication of 0 or 3 Mg ha~^ of dolomitic lime in 2000 to plots with or without the previous lime application. Liming caused total organic C (TOC) accumulation, especially in the 0-to 2.5-cm layer. The amount of TOC stored in the 20-cm layer was 49.9, 52.9, 52.7, and 57.5 Mg ha"^ in the control, 6 + 0, 0 + 3, and 6 + 3 Mg ha"^ treatments, respectively. The levels of particulate organic C (POC) and mineral-associated organic C (MAOC) in the SOM were also enhanced by liming. The increase in POC was directly related (R^ = 0.99, P = 0.002) to the accumulation of C from crop residues, which was greater in the plots receiving lime treatment. There were positive correlations between TOC and C extractable with hot water, total polysaccharides, and labile polysaccharides. The correlation analysis also demonstrated that TOC was more tightly correlated with POC than with MAOC, indicating a greater influence of the labile fraction on the increase in TOC with surface liming.

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Resumo -O objetivo deste trabalho foi avaliar a resposta de genótipos de milho (Zea mays L.), cultivado em sistema de plantio direto, a diferentes quantidades de palha de aveia-preta (Avena strigosa Schreb.) e doses de nitrogênio. O experimento foi conduzido em um Latossolo Vermelho eutrófi co, em delineamento experimental de blocos ao acaso em parcelas subsubdivididas, com três repetições. As parcelas principais foram representadas pelas quantidades de palha na superfície do solo (sem palha, 5,16 e 10,32 Mg ha -1 ). As subparcelas foram representadas por três genótipos de milho e as subsubparcelas constituíram-se das doses 0, 60, 120, 180 e 240 kg ha -1 de nitrogênio. O aumento da dose de nitrogênio reduziu a requeima das folhas e promoveu o suprimento adequado de nitrogênio das plantas de milho em todos os tratamentos com palha de aveia-preta. Os genótipos de milho diferenciaram-se quanto à produtividade de grãos, ao aproveitamento do nitrogênio mineralizado da palha e ao comprimento do sistema radicular, quando submetidos a diferentes quantidades de palha de aveia-preta e de nitrogênio.Termos para indexação: Zea mays, defi ciência nutricional, plantio direto, produção de grãos, sistema radicular. Corn genotype performance under black oat crop residues and nitrogen fertilizationAbstract -The objective of this work was to assess the performance of corn (Zea mays L.) genotypes as affected by inputs of black oat (Avena strigosa Schreb.) residues applied on the soil surface and nitrogen fertilization under no-tillage system in a Typical Haplustox. The experiment was carried out in a complete randomized block design, arranged in split-split plots with three replicates. The main plots consisted of the amount of crop residues on the soil surface (no crop residue, 5.16 and 10.32 Mg ha -1 ). The split plots were three corn genotypes, and the split-split plots were fi ve nitrogen rates: 0, 60, 120, 180, and 240 kg ha -1 . An increase in the nitrogen rates decreased nitrogen defi ciency and provided an adequate nitrogen supply for corn, under all the amounts of black oat residues. The corn genotypes grown with different amounts of black oat residues and nitrogen rates had different grain yield responses, use of mineralized nitrogen from crop residues, and root growth.

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