Injurious effect of root excretion in densely planted seedlings of fruit trees

Abstract

1. The present study was intended to confirm the existence of the toxic substance excreted from the roots of peaches by conducting the spacing experiment with peach and Japanese persimmon seedlings. Seedlings were regularly planted over the plots in regular square arrangement at five different grades of density (6.25-400plants/m2). 20-32 plants were sampled from each plot, and the results of growth measurement were discussed mainly based on total dry matter (yield) per unit area.2. In the case of Japanese persimmons, the yield per unit area (y) increased with the density of existing plants (ρ), approaching an almost constant level toward highest range of density. The result well fitted the reciprocal equation of density effect, 1/y=A+(B/ρ), proposed by SHINOZAKI and KIRA (1956), regardless of the differences in experimental period, amount of fertilizer and soil texture, although the asymptotic yield (1/A) at higher densities differed according to different treatments (Fig. 1).3. The yield-density relations in peaches were quite the same with those in Japanese persimmons when the experimental period was 112 days after the sowing, or when peach seedlings were planted in sand. However, when the experiment with peaches was continued for 163 days or more in clay loam, the yield was the highest at intermediate range of density (initial density 25-44plants/ m2) and decreased distinctly at very high density (100-400plants/m2) (Fig. 3, 4 and 5). In the latter case, the reciprocal equation failed to fit in with the experimental results.4. It may be concluded that in certain kinds of fruit trees under very high density, the growth is inhibited, not only by the deficiency of light, nutrients, etc, but also by the accumulation of toxic substance excreted from their roots. The reduction in growth seems more intense in the species as peaches which produce abundant toxin. The intensity seems to be also influenced by such factors as soil texture.