Ecological Studies on Establishment and Development of Zoysia japonica STEUD. - Dactylis glomerata L. Association after Clearing of Deciduous Broad-leaved Forest : III. Effect of fertilization on changes in shoot densities and weights of Z.japonica and D.glomerata oversown as mixture

The association of Z. japonica and D.glomerata is useful as a low-input and stable pasture for beef cattle grazing in the mountaneous area of Japan. The methods of establishment and management of association were studied from an ecological view point. Seeds of Z. japonica and D. glomerata were oversown without tillage after clearing of deciduous broad-leaved forest in Sep., 1980. The three different amounts of chemical fertilizers were applied to the treatment plots were grazed by beef cattle for 5 years. The effect of fertilization on changes in shoot densities and weights of Z. japonica and D. glomerata under the grazing condition were examined in this report. 1) Shoot density of D.glomerata was approximately 500 shoots/m^2 during 5 years after start of grazing in the non fertilized plot, although it was the lowest among all plots. 2) Shoot density of Z. japonica in the non fertilized plot was 284 shoots/m^2 in the first year after start of grazing. It increased year by year and surpassed that of D. glomerata after the third year. The density of Z. japonica in the low fertilized plot increased slightly year by year (12-64 shoots/m^2), but was relatively low level until the last year. However, seedlings of Z. japonica disappeared in the second year in the high fertilized plot. 3) Standing crop in the non fertilized plot was very few (38.7g DM/m^2) in the first year. However, it increased at 110.2g DM/m^2 in the second year due to active regrowth of D. glomerata. From the fourth year regrowth of D. glomerata reduced, and Z. japonica expanded as an alternative. Therefore, standing crop in the non fertilized plot increased continuously as a whole and reached at 273.3g DM/m^2 in the fifth year, the amount of which was similar to that in the low fertilized plot. 4) The amount of available forage for grazing cattle in the non fertilized plot was estimated to be a quarter of in the high fertilized plot, although there was an exception of low amount in the first year. 5) Vertical distribution of underground parts in the non fertilized plot indicated that D. glomerata which dominated in the first year would be gradeually replaced by Z.japonica. 6) From these results no fertilization was indispensable for the establishing Z. japonica-D. glomerata association after clearing of deciduous broad-leaved forest. However, once the stand was established, small amount of fertilization (about 20-30 kgN/ha/year) should be applied to keep vegetational equilibrium between both species.