Kee-Choon Park

Short-term effects of organic waste amendments on soil biota: responses of soil food web under eggplant cultivation

The aim of this study was to investigate the effects of reusable organic wastes on soil organisms, with a focus on changes in the soil food web. Bone meal, de-oiled cake, and oyster shell were applied at 5 t ha–1, and the abundance and biomass of soil organisms were measured at 4, 8, and 13 weeks after treatment in soil under eggplant cultivation. The abundance of microflora and fauna was higher in the soils treated with bone meal or de-oiled cake than in untreated soils, suggesting that soil organisms are affected by the quality of applied organic wastes. Increases in the abundance of bacterivorous nematodes were observed under treatment with bone meal or de-oiled cake, but there was little change in the abundance of predatory nematodes. A positive response of microarthropods in the Collembola and Oribatida was apparent, and these organisms are involved as secondary consumers in the soil food web, but the predaceous Gamasida were relatively unaffected. The abundance of protozoa, microbivorous nematodes, Collembola, and Oribatida was correlated with the abundance of bacteria and fungi, indicating that both bacteria- and fungi-based food webs formed. The abundance of the secondary consumers was not significantly correlated with that of the predators. The study suggested that, in the short-term, organic waste alters the primary and secondary consumers but its effect may not extend to predators.

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

Abstract 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.

Effects of Vermicompost Application on the Growth and Ginsenoside Content of Panax ginseng in a Reclaimed Field

The objective of this study was to evaluate the effects of the application of vermicomposts on the growth parameters and ginsenoside content of ginseng roots. Food waste vermicompost (FW), cow manure vermicompost (CM), and paper sludge vermicompost (PS) were applied at 10 and 40 t ㏊ -1 , respectively. One-year-old seedlings were transplanted and 4-year-old roots were harvested. Soil nitrate and phosphate concentrations were increased in the plots applied with FW and CM at 40 t ㏊ -1 . Soil pH and exchangeable Caconcentrations were higher at FW 40 t ㏊ -1 than at CM 40 t ㏊ -1 . Root yield increased when treated with FW 40t ㏊ -1 in comparison to the yield for the control. The incidences of root rot disease and ginsenoside content were not significantly affected by the treatments. The results suggested that application of vermicompost might not show a relationship between root biomass and ginsenoside content. It further showed that proper use of vermicompost can promote root yield without a reduction in root quality or an increase in the incidence of root rot disease in reclaimed fields.

Effect of Continuous use of Inorganic Fertilizer on the Soil Organisms and Food Chain

BACKGROUND: This study aimed to evaluate the combined effects of three components (NPK) of chemical fertilizers with basal application of compost on soil organisms.METHODS AND RESULTS: The soil was treated with five treatments continuously for 15 years: control, PK, NK, NP and NPK. The application of N increased plant growth or biomass, and enhanced organic matter content in the soils. Levels of microbial phospholipid fatty acids (PLFAs) in the soils did not show marked differences among the soils treated with different treatments. However, the principal component analysis showed the changes in the structure of the microbial community in the soil, depending on treatments added. Nitrogen application caused a decrease of pH and an increase of EC in the soils, and these environmental stresses appeared to offset the promoting effect of increased organic matter content on microbial abundance. The abundance of bacterivorous nematodes was the highest in the soils after treating NPK; however, the abundance of fungivorous nematodes was unaffected. There was no significant correlation between the abundances of microbial groups and their feeders. Organic matter content was significantly correlated with the abundance of nematodes in the soils.CONCLUSION: Our results showed that chemical fertilizers affect the soil food chains through both biotic and abiotic factors, and a trophic cascade in the soils may not occur in response to long-term fertilization.

Effects of the Applications of Chitin and Chitosan on Soil Organisms

Effects of chitin and chitosan treatments on soil microorganisms and the mesofauna were investigated in a microcosm and a fumigated field experiment. Responses of microorganisms were determined using microbial phospholipid fatty acid (PLFA) analysis, whereas responses of the mesofauna were measured in terms of the abundances of nematodes and microarthropods. Soil nitrate concentration increased on the application of chitin. Overall, chitin promoted bacterial and fungal abundance, leading to an increase in abundance of free-living soil nematodes that feed on decomposers. The ratio of saturated to unsaturated fatty acids was highest in the chitin-treated soil. Chitosan had a minimal effect on the abundance of microorganisms; however, it reduced the abundance of collembolans in the microcosm experiment. These results indicate that the application of chitin has beneficial effects on the supply of nutrients and promotion of the abundance of soil organisms.