Parthenium hysterophorus L. is a widely distributed terrestrial weed. It has been shown to contain parthenin, a sesquiterpene lactone. Parthenin has been reported as a germination and radicle growth inhibitor in a variety of dicot and monocot plants and it enters the soil through the decomposing leaf litter. The methane potential of untreated and NaOH-treated Parthenium in anaerobic, laboratory-scale digesters has been reported in detail earlier. Anaerobic digestion of Parthenium biomass generates an effluent (liquid and sludge). The effluent from the NaOH-treated Parthenium fermenter had high concentrations of Na+ and Cl−. This study focuses on the utilisation of the effluents as manure and examines the impact of anaerobic digestion on the inhibition potential of Parthenium. Pearl millet (Pennisetum glaucum) seeds were used to bioassay the inhibition potential. It was found that the seed germination and radicle growth were inhibited at ≥10 g total solids (TS) l−1 and 15 g TS l−1 Parthenium dried solids (DP) treatment, respectively. There was no inhibition of plumule length in the DP treatment. The untreated Parthenium fermenter effluent (UPFE) significantly (P<0.05) increased germination. The radicle and plumule lengths were significantly (P<0.05) higher up to the 30 g TS l−1 UPFE treatment, relative to the control treatment, with de-ionised water. Data for the NaOH-treated Parthenium fermenter effluent (NPFE) showed inhibition of the germination only in the 30 g TS l−1 treatment. Above 15 g TS l−1, there was inhibition of radicle length and inhibition of plumule length occurred only at 30 g TS l−1. The inhibition in the NPFE treatment was related to the high concentration of chloride ion in the NPFE. The results of this study showed that DP is a potential germination and radicle growth inhibitor and anaerobic digestion of DP could have biodegraded the inhibitor as evidenced from the enhanced germination and seedling growth in the UPFE. This study also showed that anaerobic digestion of DP conserved the NPK content and both the effluents could be land applied as organic manure.
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