ABSTRACT Corn intercropped with Urochloa brizantha (Syn, Brachiaria brizantha) has been indicated as a suitable alternative management practice for rational land use in crop-livestock production systems in the Cerrado region of Brazil. An experiment was carried out in Maracaju, MS, Brazil to evaluate the effect of sequences of soybean/second-crop corn systems intercropped with Urochloa brizantha and the effects of forms of nitrogen on soil chemical and physical properties. A randomized block experimental design was used with four replications; treatments were in a 2 × 4 factorial arrangement with two systems of crop management: second-crop corn intercropped with Urochloa brizantha, and monoculture of second crop corn; and four forms of topdressing N: urea, urea + ammonium sulfate, ammonium sulfate, and no N supply. The following chemical properties were evaluated: soil organic matter and exchangeable K contents, cation exchange capacity, base saturation, and K saturation; as well as the physical properties: soil bulk density and aggregate stability. Crop residue cover and agronomic traits of soybean were also assessed. Intercropping induced significant differences in crop residue cover, plant height, soybean yield, stand, 100-seed weight, soil organic matter, exchangeable K, and K saturation in the exchange complex. There was no significant effect of the crop sequences on soil bulk density and mean weight and geometric mean diameter of water-stable aggregates. No significant effect of forms of N was observed on any chemical or physical properties, or on those related to soybean development.

A competitividade econômica da soja brasileira no mercado mundial se deve, em grande parte, aos benefícios da fixação biológica do nitrogênio na cultura. O trabalho foi conduzido a campo, sob sistema plantio direto, em condição de sequeiro, no Município de Maracaju-MS, com o objetivo de avaliar a nodulação, o crescimento, nutrição mineral e produtividade de grãos da soja submetida a diferentes doses de gesso agrícola e molibdênio. Foi utilizado o delineamento experimental de blocos ao acaso, com cinco repetições e esquema de parcelas subdivididas, sendo as parcelas representadas por quatro doses de gesso agrícola (0, 1.000, 2.000 e 3.000 kg ha-1) e as subparcelas, por quatro doses de molibdênio (0, 20, 40 e 60 g ha-1). Não houve efeito da interação gesso x Mo sobre a produtividade da soja. O gesso agrícola não influencia no teor foliar de N e na produtividade. O Mo proporciona incrementos na produtividade e no teor de proteínas dos grãos.

The economic competitiveness of Brazilian soybeans on the world market occurs, in large part, due to the benefits of biological nitrogen fixation in this crop. The field experiment was carried out in Maracaju, Mato Grosso do Sul State, Brazil, under no-tillage system, in rainfed condition. The aim was to evaluate nodulation, growth, mineral nutrition and grain yield of soybeans under different doses of gypsum and molybdenum. The experimental design used was a randomized block with five replicates and arranged in a split-plot squeme, with the plot represented by four doses of gypsum (0, 1.000, 2.000 and 3.000 kg ha-1) and the subplots by four doses of molybdenum (0, 20, 40 and 60 g ha-1). There were no interaction effects of Mo x gypsum for grain yield. Gypsum has no influence in the N leaf content and grain yield. Mo increases grain yield and protein levels in the grain.