Reduction in Saturated and Unsaturated Hydraulic Conductivities of an Andisol by Vinasse Application

Abstract

With the increase in the production of bioethanol, it has become urgent to establish a sustainable system for recycling vinasse that includes its application to land. The purpose of this study was to determine the impact of vinasse application on the hydraulic properties of the soil. An incubation experiment was conducted to investigate the biological effects. Temporal changes in both saturated and unsaturated hydraulic conductivities [Ks and K(ψ), respectively] after applying vinasse were measured by the falling‐head method and the steady‐state flux control method, respectively. After vinasse application, the number of bacteria increased by one order of magnitude, whereas the number of fungi increased by two orders of magnitude compared with a test with deionized water. A remarkable reduction in Ks was observed within the fourth day after vinasse was applied instead of deionized water. The reduction in Ks was due to both biological and physical clogging. We attempted to determine what factors contributed to these effects on the Ks reduction and found that 73 to 92% of the Ks reduction was caused by physical clogging due to suspended solids. The temporal reduction in K(ψ) was within one order of magnitude; however, the values of K(ψ) dropped by two orders of magnitude for the same matric potential (ψ) value at the end of each column experiment. Moreover, 91% of the increase in the total amount of organic matter came from vinasse. From the experimental results, we concluded that the reductions in both Ks and K(ψ) occurred during vinasse application and the main reason for the reductions was the physical clogging due to suspended solids.