This research is aimed at evaluating the effects of the glycerin effluent from the biodiesel industry resulting from chemical processes involving the transesterification of triacylglicerides in bio-oils, a reaction catalyzed with potassium hydroxide. This glycerin material (hereinafter referred to as "K-glycerin") may be assumed to be a potential source of potassium to increase the yields of soybean crops and to promote corresponding alterations in some chemical and microbiological properties of the soil. Two field assays were conducted on two soils classified (i) Typical Hapludox (Perox suborder of the Oxisol order, according to the USDA Soil Taxonomy System. In this work, this site was identified simply as TH) and (ii) Typical Quartzipsamment (Aquents suborder of the Entisols order; TQ), in the state of Minas Gerais, Brazil. The used treatments were: (i) four doses (corresponding to 0, 40, 80 and 160 kg ha-1 K2O) on the TH soil and four doses (corresponding to 0, 60, 120 and 240 kg ha-1 K2O) on the TQ soil form, and (ii) two potassium sources (specifically, KCl and K2SO4) at a K2O equivalent doses of 80 kg ha-1 on the TH soil and 120 kg ha-1 on the TQ soil. The soybean yields resulting from the application of K-glycerin were found to be related to the availability of K in the soil and this source supplied in part the need of potassium by soybean crop. The K-glycerin does not cause any readily detectable harmful or environmental effect to these cropping sites; however, further detailed studies are needed to better evaluate the long-term use to understand the soil ions dynamics under the soybean crop.
Key words: Organic residue, yield, nutrition, soil, microbial biomass.
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