Evaluation of phytotoxicity of composts produced from spent mushroom substrate using seed germination bioassay of Raphunus sativus L.

Abstract

present study, a seed germination test was conducted to evaluate the possible phytotoxic effect of SMS compost. Aqueous extracts from compost produced by SMS, amending different N sources (green leaves and urea) with and without an inoculum as 25%, 50%, and 100% were tested against seed germination of radish (Raphanus sativus L). According to the results, the lowest Germination index (GI%) was observed in 100% compost aqueous extractions while the highest GI% was observed in 25% compost aqueous extracts. GI% of inoculated compost has positive significant correlations with both relative seed germination (RSG%) and relative root growth (RRG%) [r=0.600, p=0.05 and r=0.965, p=0.01, respectively]. The regression of GI% and EC values in inoculated (r2=0.7064) and non-inoculated (r2=0.6009) extracts showed negative linear relationship. Moreover, the EC was significantly correlated with all extractable tested ions except Cu2+ and Ni2+ in inoculated treatments. pH values in all aqueous extracts recorded in the range of 6.27 to 8.08. Extractable elements Cu2+ (r=0.645, p=0.01) and Zn2+ (r=0.577, p=0.05) had positive correlation with pH. The water extractable NH4+ concentration was significantly higher (p<0.05) in the inoculated SMS compost amended with urea and it was significantly lower (p<0.05) in non-inoculated SMS compost amended with Tithonia and inoculated SMS compost without amendments. Further, the inoculated SMS compost extracts showed higher performance in GI% and RRG% than non-inoculated SMS. Therefore, SMS can be recycled as compost integrating nitrogenous materials and inoculum to use safely as a soil amendment on seed germination.