Assessment of the Environmental Impact of Yeast Waste Application to Soil: An Integrated Approach

Abstract

The yeast production industry (e.g. distillery, brewing, baking industries) has been growing globally over the last years generating a large amount of sub-products rich in organic matter that could be used as soil improvers or organic fertilizers. A set of laboratory experiments were performed to investigate the impact of yeast waste application to an acidic sandy soil on potential nutrient leaching and gaseous emissions. Experimental treatments were: surface application of yeast (CMSs) and decanted-yeast (CMSds), surface application of yeast (CMSm) and decanted-yeast (CMSdm) followed by incorporation in the 0–5 cm soil layer, surface application of ammonium nitrate (AN) and unfertilized soil (CTR). A leaching experiment (73-day period) with six irrigation events every 2 weeks was performed (6 treatments × 4 replicates) to assess N and P losses. Two parallel incubations (6 treatments × 3 replicates) were simultaneously performed to measure GHG emissions (CO2, N2O, CH4) and to assess the N mineralization in each treatment. Results showed that yeast application increased initial NH4+ concentration in leachates and soil relative to unfertilized soil and NO3− concentrations increased afterwards. Furthermore, yeast waste led to a significantly increase of N2O and CO2 in the first days of incubation. Gaseous emissions in AN treatment were very similar to unfertilized soil even if a small increase of N2O was also observed. CH4 emissions were insignificant in all treatments during the whole experiment. It is still to refer that the global warming potential of yeast and AN treatments were 6× and 2× times higher than control, respectively. Our results obtained in an acidic sandy soil allow concluding that yeast waste can be applied to soil as organic fertilizer since it provide not only nitrogen and potassium to plants but also contribute to increase soil organic matter content. Nevertheless, the potential nitrate leaching and increase of GHG emissions induced by yeast application to soil have to be carefully monitored to avoid environmental problems. Similar studies using different soil types as well as field experiments are still needed to confirm our conclusions.