Abstract
Five field crops, sugar beet (Beta vulgaris L.), potato (Solanum tuberosum L.), spring wheat (Triticum aestivum L.), soybean (Glycine max Merr.), and adzuki bean (Phaseolus angularis L.) were planted continuously or rotationally for 16 years in northern Japan by using almost the same cultivation method during the 16 years. In 10 continuous cropping plots, organic matter was applied to 8 plots throughout the 16 years, and soil fumigation was conducted in 3 plots in the last 6 years. Soil was fumigated with 1,3-dichloropropene (D-D) or trichloronitromethane (chloropicrin). We investigated the yield of each crop from 11 to 16 years. The yield decrease by continuous cropping was significant in sugar beet, soybean cultivar susceptible to soybean cyst nematode and adzuki bean. Available nitrogen in soil was increased by organic matter application. The yield of sugar beet was increased by organic matter application, probably through the increase in available nitrogen in soil. However, even when available nitrogen concentration in soil was almost the same, the yield of sugar beet in continuous cropping was lower than that in rotation cropping. This suggested that sugar beet could not sufficiently utilize available nitrogen in soil in continuous cropping. In continuous cropping of sugar beet and adzuki bean, soil fumigation increased the yield independent of the concentration of available nitrogen in soil. Therefore, it was suggested that this effect of soil fumigation was caused by soil sterilization.
