Abstract: Allelopathic effect of root exudates on pathogenic fungi of root rot in continuous cropping soybean was studied by sand culture, water culture, and indoor culture experiments. The results showed that allelopathic promotion of root exudates on the growth of Fusarium semitectum, Gliocladium roseum and Fusarium oxysporum, especially Fusarium semitectum reached significant level or especially significant level in continuous cropping soybean compared with the control. Allelopathic promotion of root exudates on the growth of Fusarium semitectum and Gliocladium roseum in continuous cropping soybean was distinctly larger than that in rotation soybean, and the difference reached significant level under their low concentration. Allelopathic promotion of high concentration of root exudates on the growth of Fusarium semitectum was smaller than that of low concentration of root exudates, and the difference reached significant level in continuous cropping soybean. Allelopathic inhibition of high concentration of phthalic acid and propanedioic acid (L 5 and B 5) on the growth of Fusarium semitectum, Gliocladium roseum and Fusarium oxysporum, especially Fusarium semitectum reached significant level or especially significant level compared with the control. However, allelopathic promotion of low concentration of phthalic acid and propanedioic acid on the growth of Fusarium semitectum, Gliocladium roseum and Fusarium oxysporum partly reached significant level.

Key words: Soybean, Continuous cropping, Root exudate, Root rot, Allelopathy, slow/controlled release urea, emission of N₂O., paddy field, continuous application, ammonia volatilization