Use of Biostimulants Obtained from Okara in the Bioremediation of Soils Polluted by Imazamox

Abstract The objective of this study was to study under laboratory conditions the bioremediation effect of two biostimulants obtained from okara in a soil polluted by imazamox at a rate of 2.5 l ha-1 (manufacturer’s recommended rate). These biostimulants were obtained by enzymatic hydrolysis processes using one (subtilisine) and two (subtilisine and flavourzyme) enzymes. Their effects on soil enzymatic activities, the microbial community structure and the evolution of the herbicide in soil over a 90-day period. Both biostimulants stimulated the soil biochemical activity and microbial population. However, this stimulation was greater in the soil amended with the biostimulant with a higher percentage of low-molecular-weight proteins (<300 Da). Applying the biostimulants to the polluted soil decreased the inhibition of the biological properties. This decrease was also greater when the biostimulant had a higher content of low-molecular-weight proteins content. Consequently, the biostimulant obtained by hydrolytic processes using the subtilisin and flavourzyme enzymes would be of greater interest in the bioremediation process.