Effects of rice husk and rice husk biochar on root rot disease of ginseng (Panax ginseng) and on soil organisms

This study investigated the effects of rice husk and rice husk biochar on root rot (caused by Cylindrocarpon destructans and Fusarium solani) of ginseng (Panax ginseng) and on soil organisms. The effects were compared between paddy-converted and upland soils characterised by high and low nutrient content, respectively. The prevalence of root rot disease in the upland soil decreased in plots treated with rice husk at 5.2 Mg ha−1 compared to the untreated control. Small differences in soil chemical properties between different treatments suggested the role of biotic factors in the suppression of the disease. In both soils, the lowest hyphal growth of Fusarium solani was observed in soil collected from plots treated with rice husk at 5.2 Mg ha−1. The results suggested that the low incidence of root rot disease was due to the suppressive effect of soil on pathogenic fungi in the treated upland soil. Principal component analysis of phospholipid fatty acid results suggested that changes in microbial community structure contributed to soil suppressiveness in the paddy-converted soil. The highest density of fungivorous nematodes was observed with rice husk at 5.2 Mg ha−1 in the paddy-converted soil, and Aphelenchus sp. collected from the plots were successfully cultured on F. solani and C. destructans. This observation showed that the fungivorous nematodes have potential to suppress pathogenic fungi by feeding on them. It was shown that rice husk can be used in control of root rot disease while promoting the growth of beneficial organisms suppressing pathogenic fungi and that the effect may differ by soil type.