Arbuscular mycorrhizal (AM) fungi improve the uptake of phosphate from soil through symbiotic associations with plant roots. The introduction of winter crops has been shown to increase the nutrient uptake and yield of subsequent crops and may result from increased AM fungal density in the soil. However, there is little information regarding the effects of different winter crops on AM fungal communities in roots of various winter crops. The present study is an evaluation of the impact of various winter crops on AM fungal community structure in winter crop roots. A two-year field experiment was conducted at Nihon University in Kanagawa, Japan. Replicated plots of winter sown wheat, spring sown wheat, and canola were established in 2007, and plots of wheat, red clover, and canola were established in 2008. After the winter crop, soybean was sown in all plots. The AM fungal community structure in winter crop roots was characterized on the basis of the large subunit ribosomal DNA (LSU rDNA). Glomus was dominant in roots of winter- and spring-sown wheat; however, Scutellospora, and Gigaspora were only found in roots of spring-sown wheat. In 2008, Glomus was again dominant in wheat and red clover; however, Acaulospora, Scutellospora, and Gigaspora were found only in red clover. Thus, the selection of a winter crop has the potential to change the community structure of AM fungal communities and may have implications for the productivity of the subsequent crop.

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Soil microbial biomass and microbial respiratory activity were investigated in organic matter, such as leaves and stems of crotalaria, cattle manure compost and bark compost. The type of organic matter strongly influenced the soil microbial characteristics. While the microbial biomass increased with the application of organic matter, the degree of increase differed according to the variety of organic matter. The microbial biomass increased in the plots in the following order: leaves of crotalaria > stems of crotalaria > cattle manure compost, but it did not increase with the application of bark compost. It reached 1700 mg C kg^<-1> dry-soil in the plot containing leaves of crotalaria one day after application. Microbial respiratory activity increased with the application of crotalaria leaves and stems but not with that of cattle manure compost and bark compost. The respiratory activity decreased gradually in each plot to a similar level to that of the no-organic-matter-added plot after 15 days. Organic matter used in this study was classified into three types: one that increases only the biomass, one that increases both the biomass and respiratory activity, and one that increases neither.

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The Kanagawa Agricultural Technology Center has been testing the effect of a compost consisting of okara and coffee residue (OC) on Japanese radish cultivation since 1996. It is known that damage by the root-lesion nematode to Japanese radish was less severe in OC-soil than in a soil amended with cow manure compost (CM). In this study, the effects of amendment with OC-compost on soil communities of nematodes and microbes were investigated and compared with those of amendment with CM and chemical fertilizer (CF) in 2006 and 2007. There were no significant differences in total carbon among the three soils, but the soil microbial biomass was significantly higher (ca. 2.5 times) in OC- and CM-soils than in CF-soil. Glucose decomposing activity was the highest in OC-soil, followed by CM-soil and then CF-soil. There was no significant difference in the density of the root-lesion nematode, but that of free-living nematodes was significantly higher in OC- and CM-soils than in CF-soil. The community structures of nematodes and fungi in the soils and of bacteria on the Japanese radish surface, as analyzed by PCR-DGGE, were different among the three soils in both years, while the soil bacterial community was not different. Unique bands were detected in OC- and CM-soils in most of the DGGE profiles, suggesting enrichment of specific microbes and nematodes by the organic matter application. Collectively, amendment with OC- and CM-compost increased the soil microbial activity and biomass and affected the soil microbial and nematode community structures. OC-compost increased the soil microbial activity more than CM-compost did.

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[in Japanese]

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[in Japanese]

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[in Japanese]

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[in Japanese]

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[in Japanese]

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