DEGRADATION OF PHENOLICS IN DIGERA MURICATA: PHYTOTOXIC EFFECTS OF ROOT AND SHOOT LEACHATE PLUS N FERTILIZATION ON THE GROWTH OF MILLET

Abstract

Digera muricata was found to be highly allelopathic in nature. Phenolic compounds (quercetin, sinapic and ferluic acid), alkaloids (cystine and berbine) and a terpenoid (limonene) was detected from root and shoots of D. muricata. Decaying plant material of D. muricata inhibit not only the germination and growth of neighbouring species but it is also self inhibitory. When plant matures and dies down, the leachates having greater concentrations of phenols enter the soil. At this time the leachate is highly concentrated but with the passage of time it undergoes degradation and level of phenolic declines. Thus allowing the germination of other plants. Therefore, the present study was designed to reveal the degradation process of phenolic compounds in the soil Moreover, adverse effects of phenolic compounds on the growth of bullrish millet, the most susceptible crop plant.was also studied. For this purpose different levels of nitrogen fertilization (0 mM, 1 mM and 5 mM) were added to the soils having different dilutions of decaying root and shoot leachate of D. muricata (fullstrength, 1/2 strengthand 1/4 strength). Addition of nitrogen to the soil showed significant decline of phenolic compounds with time, because nitrogen might increase the microbial activites in the soil, which lowered the phenolic levels, thus ameliorating growth rates. Concentration of phenolic compounds were greater in the soil having full-strength root/shoot leachate with 5 mM N fertilization, followed by by 1 and 0 mM N fertilization. Growth of millet was significantly higher in the controls having no plant leachate followed by 1/4 and 1/2 strength root/shoot leachate. Dry weights were considerably lower in full-strength plant leachate. Whereas, 5 mM N fertilization showed maximum growth followed by 1 and 0 mM N fertilization. Relatively root leachate was found to be more toxic than shoot leachate.