Urochloa ruziziensis Desiccation, Straw Quantity and Position on Nodulation and Production of Soybean ‘M-SOY 7908 RR’

This study aimed to evaluate the effects of the quantity and soil position of Urochloa ruziziensis straw desiccated with glyphosate for different periods of time on ‘M-SOY 7908 RR’ soybean nodulation, growth and production characteristics. Three experiments were conducted under semi-controlled conditions. In the first, three quantities of U. ruziziensis straw (2.5, 5.0 and 10 ton ha-1) previously desiccated with glyphosate were incorporated into the soil (10 cm deep) or deposited on the soil surface, and in the second experiment, the treatments consisted of three U. ruziziensis desiccation periods, 0, 7 and 12 days before soybean sowing, and one treatment without U. ruziziensis. In the third treatment, desiccation was performed at 0, 5 and 10 days before soybean sowing, and the desiccated plant shoots were removed or left in place before soybean sowing. For each of the experiments, a completely randomized experimental design was adopted, and the masses of the shoot and root dry matter, the degree of nodulation and soybean production were evaluated. The deposition of U. ruziziensis straw on the soil surface promoted the nodulation and growth of ‘M-SOY 7908 RR’ soybean plant shoots, while its incorporation into the soil, even at 2.5 ton ha-1, caused deleterious effects. Desiccation of U. ruziziensis from 0 to 7 days before sowing was also detrimental to the nodulation and growth of M-SOY 7908 RR soybean, reducing its productivity. RESUMO: Objetivou-se neste estudo avaliar o efeito da quantidade e do posicionamento de palha de U. ruziziensis, dessecada com glyphosate em diferentes épocas, sobre a nodulação, o desenvolvimento e as características produtivas da soja M-SOY 7908 RR. Para isso, foram conduzidos três experimentos sob condições semicontroladas. No primeiro, os tratamentos constituíram-se da incorporação (a 10 cm de profundidade) ou deposição na superfície do solo de três quantidades de palha de U. ruziziensis (2,5, 5,0 e 10 t ha-1), previamente dessecada com glyphosate. No segundo experimento, os tratamentos constaram de três épocas de dessecação de U. ruziziensis: 0, 7 e 12 dias antecedendo a semeadura da soja, e um tratamento sem U. ruziziensis. Para o terceiro, realizou-se a dessecação aos 0, 5 e 10 dias antecedendo a semeadura da soja, retirando-se ou não a parte aérea da planta dessecada, antes da semeadura da soja. Foram avaliadas a massa de matéria seca da parte aérea e raízes, a nodulação e a produção da soja. Em todos os ensaios, o delineam