1. The present study was to investigate the ecology of peach trees, especialy their early defoliation in the orchards of light sandy-loam soil of volcanic origin.
Young peach trees were planted in the pots, and owing to the kinds of soils and the amount of compost which was added to one pot, the experimental plots were named as follows ;
volcanic ash soil (V.A.S.), volcanic ash soil＋compost 0.5Kan (V.A.S.+ COM.0.5), volcanic ash soil＋compost 1.0 Kan (V.A.S.+ COM.1.0), paddy soil (P.S.), river sand (R.S.) and river sand + compost 0.5 Kan (R.S.+ COM.0.5).
2. From the viewpoints of new shoot length and increased weight of trees, V.A.S. was better than R.S., but worse than P.S. and both plots of volcanic ash soil added compost were compared quite well with P.S.
3. In each plot of volcanic ash soil, the older leaves began to be shed early in June and this early defoliation spread progressively towards the upper leaves, however its symptom could not be noticed in P.S. and R.S.
Degree of this defoliation was slightly lightened in proportional to the amount of added compost.
4. Results of the leaf analysis were as follows ;
the N content of V.A.S. was higher and Ca, Mg was exceedingly lower than that of P.S., especially Mg content (0,14% on dry matter) was noticeably low.
This Mg content was lower than that of R.S., of which content of each element was generally low.
5. Results of the soil analysis after growth season showed that contents of replacable Ca and Mg in V.A.S. were about one to twenty as compared with P.S. and the content of each element without Mg in V.A.S. was higher than that in R.S.
6. As the result of this study, it's suggested that early defoliation of peach trees in V.A.S. is caused by the deficiencies of Ca and Mg, especially that of Mg and can not be controlled by the compost added in the soils.