Abstract This work aimed to study different seeding rates in soybean, at management zones determined by the mapping of the soil apparent electrical conductivity (ECa) and its relationships with plant phenology and grain yield (GY). The experiment consisted of a completely randomized design, with six replications. The plant population ranged between 311,000, 360,000, and 422,000 plants ha-1, and the fixed population (360,000 plants ha-1). The management zone with the least yield potential, received the highest seed population. The management zone with the highest plant vigor potential, received the lowest seed population. The variables plant height, Normalized Difference Vegetation Index (NDVI) at 50, 66, and 92 days after emergence (DAE), one hundred-grain weight, and GY were analyzed. ECa maps can be used to decide the seed population of the soybean. The decision strategy of increasing 20% of the seed soybean population on the smaller ECa map zones, and decreasing 20% seed population on higher ECa zones was effective and resulted in similar GY, even with the negative pressure of the high resistance of penetration (RP) values in some zones. GY map variability was influenced by ECa 0-0.2 m, by NDVI at 92 DAE and by RP 0.4-0.6 m soil layer.

Está sendo desenvolvida uma nova tecnologia, chamada Agricultura de Precisão e, com ela, vêm surgindo novos equipamentos, capazes de realizar a aplicação localizada de defensivos. Muitos desses equipamentos necessitam de um mapeamento prévio do alvo de interesse para sua utilização. O propósito deste trabalho foi a avaliação de uma metodologia prática para o mapeamento de plantas daninhas pelo contorno das reboleiras com um quadriciclo. Foram realizados dois mapeamentos em um mesmo campo agrícola, com quinze dias de intervalo. A metodologia aplicada para o mapeamento de plantas daninhas mostrou-se eficiente nas condições avaliadas. Foi possível a obtenção dos mapas de plantas daninhas com três níveis de infestação. Verificou-se a necessidade de um planejamento para a realização do mapeamento, levando-se em consideração a posterior aplicação localizada de defensivos.

Several items of equipment able to realize site specific chemical application have been developed. Equipment for site specific chemical application needs a prescription map of the target area. The purpose of this work was to evaluate a practical method for weed mapping by driving over the patch contour with an All Terrain Vehicle (ATV). Two weed maps were created for the same agricultural field. The proposed method for weed mapping was considered efficient for the evaluated conditions. The weed maps obtained showed three infestations levels. An important conclusion obtained was that timing to perform the weed mapping is a very important factor to be considered for site specific chemical application.