林木稚苗の生育に及ぼす密度と施肥量の影響

Abstract

It is very important to increase the yield of forest land and to shorten the harvest time. Concerning with this problem, the following has been found. (a) The yield in unit area increases with the increase of density up to a certain limit. (b) Fertilizing has great influences on the productivity of forest land or nursery. We carried out some experiments in various combinations of density and amount of fertilizer. The kinds of trees experimented are SUGI (Cryptomeria japonica D. Don.), HINOKI (Chamaecyparis obtsusa S. et Z), KUROMATSU (Pinus Thunbergii), SLASH PINE (Pinus elliottii var. elliottii) and MOLLISSIMA ACACIA (Acacia decurrence var. mollissima Willd). The experimental plan and the results are shown in the tables, 1, 15, 18, 21, 25, and 3-14, 16-17, 19-20, 22-24, 26-28. The conclusion of these experiments is as follows. 1) It was recognized for all the kinds of trees experimented with that the competitiondensity law can be applied closely, namely, the volume or weight of an individual tree decreases with the increase of the density, and the total yeild of unit area increases with the increase of the density up to a certain limit. 2) The effects of the density are larger and more remarkable in comparatively lower density in non fertilized plots than in fully fertilized plots. 3) In a certain density the volume or weight of an individual seedling and the total yield per unit area increase with the increase of the amount of fertilizer. In fully fertilized plots, bigger seedlings can be expected, even at higher density, than in lower density in less fertilized plots. 4) The total yield per unit area would become maximum at a certain density. The limit density may be over 100 seedlings. per squar meter in the case of SUGI, HINOKI or KUROMATSU which are replanted as two-year-old. 5) By sufficient and complete application of fertilizer which contains a proper ratio of the three elements of fertilizer, we can expect better seedlings which have well developed roots, than in poor soil even at higher density. 6) The grade of density effects or the influences of fertilizing on the growth of seedlings differs according to the species of tree: for A. MOLLISSIMA, SLASH PINE and SUGI it is large, and for HINOKI or KUROMATSU seedlings is little. From these results, it may be concluded that there are some other factors than light, which cause the effect of competition. The factors, nutrient in the soil give some effects on the growth of seedlings at first, and the competition for light is secondary. Fertilizing moderates the competition for light.