Residual effect of beet top and manure compost on soybeans [Glycine max] cropped following sugar beets [Beta vulgaris]

Sugar beets were confirmed to have an unfavorable effect on the growth and yield of subsequent soybeans in drytype volcanic ash soil in Tokachi District, Hokkaido. The effect was clearer on growth of stems and leaves than on yield, but no symptom of zinc deficiency was observed. Beet top, incorporated into the soil soon after the harvest of sugar beets or potatoes, enhanced soybean growth and yield the following year. Manure compost, applied before planting sugar beets or potatoes, also promoted soybean growth and yield. There was no statistical interaction between precropping treatment and beet top or manure compost application. No influence of the first year treatments was found on corn after soybeans on the third year. The deteriorating effect of sugar beets on subsequent soybeans is speculated to be caused by some allelopathic substance(s).