DECOMPOSITION OF THE REMAINING STRAW DURING SOYBEAN GROWING IN THE MIDWESTERN PARANÁ, BRAZIL

Crop biomass plays an important role, especially in tropical and subtropical crops that adopt the no-tillage system, whose decomposition is related to material composition and environmental conditions. The objective of this work was to analyze the decomposition of straw remaining from autumn/winter crops in the development of soybean in succession in the Midwest region of Paraná. The experiment was conducted between 2019 and 2021 in a completely randomized design, with eight treatments (spontaneous, black oat, brachiaria, corn, wheat, oilseed radish, corn + brachiaria, and black oat + oilseed radish) and four replications. After autumn/winter cultivation, biomass samples were dried and placed in nylon bags, returning to the original plot during soybean sowing. The decomposition bags were collected in seven periods over 120 days, coinciding with the soybean cycle. The decomposition rate was analyzed by regression. The regression equations and the amount of biomass remaining from the autumn/winter seasons were determinate the half-file and the remaining mass on the soil surface at sowing and at 30, 60, 90, and 120 days after sowing. Biomass production and decomposition rate varied with the season, depending on environmental conditions. Wheat had the lowest decomposition rate with a half-life greater than 100 days. Intercropping crops reduce the decomposition rate.