抄録
This paper discusses the use of nematode community indices for evaluating the health of agroecosystems and the effects of farming practices such as tillage and cover crop management on nematode community structure. Nematodes can be used as bioindicators of soil health because they are ubiquitous and have diverse feeding behaviors and life-history strategies, ranging from colonizers to persisters. By combining the assessment of nematode feeding groups with colonizer-persister (c-p) scaling of functional guilds, nematode faunal analysis has become a more powerful tool, allowing this phylum to be used as a bioindicator of soil health and food web condition. In a 9-year study conducted on the Kanto Plain of Japan, tillage disturbance showed a significant negative correlation with the structure index (SI) that is an indicator of food web state affected by stress or disturbance. Although cover cropping and nitrogen fertilization did not affect pathogenic nematode densities during the experimental period, cover cropping did significantly reduce the proportion of pathogenic nematodes in the total nematode abundance, and nitrogen fertilization increased the degree of rice yield reduction with greater pathogenic nematode density. Our findings suggest that no-tillage (NT) and crop rotation will be effective for controlling pathogenic nematode densities, because NT reduced their numbers and increased soil ecological diversity. Over the experimental period, SI increased not only in NT plots but also in those treated with a moldboard plow or rotary cultivator. These results suggest that increases in soil carbon foster a more diverse nematode community structure. Long-term nematode community changes will be an important focus of future research, and this information will be helpful for developing more sustainable agriculture in Japan.
