Studies on the Growth and Productivity of Maize for Whole-Plant Silage in the North-Marginal Area, Nemuro District in Hokkaido : IV. Effects of planting density on dry-matter accumulation habits and yield

[摘要] The objective of this study was to investigate the effects of planting density on the dry-matter (DM) production and yield of maize for whole-plant silage in the north-marginal area in Japan (where accumulated temperature from June to September is 1946°C). Experiments were conducted for 5 years from 1978 to 1982, based on the same design. Wase-homare (early hybrid) was grown at four planting densities from 40, 000 to 100, 000 plants/ha in 1978∼1980 and from 58, 000 to 103, 000 plants/ha in 1981 and 1982 (Table 1). DM weights in each organ and leaf area were measured at the 4th-, 7th-, 11th-leaf fully developed stages, silking stage, and, 3 and 6 weeks after silking. DM yields and percentage of barren plants were measured at harvesting date. The results obtained were as follows : I. As planting desity increased, top growth rates (TGR) during the vegetative growth period were increased. Contrarily, TGR during the ear-filling period were decreased rapidly, resulted in the minimum at the highest planting density of about 100, 000 plants/ha during the latter half of the ear-filling period (Fig. 1). It was due to rapid decrease of net assimilation rates (NAR) during the ear-filling period in high planting density causing increase of mutual shading and specific leaf area (SLA) (Table 2). 2. The optimum leaf area index (LAI), under which maximum TGR obtained, during the ear-filling period, was about 3.0 in all the years (Fig. 5). The planting density which gave the optimum LAI of about 3.0 during the ear-filling period was obtained at the planting density of 73, 000 plants/ha (Fig. 1). 3. The maximum ear growth rates (EGR) during the latter half of the ear-filling period were obtained at 60, 000∼80, 000 plants/ha, and EGR decreased at the higher planting density than the above. Furthermore, the declines of EGR at the higher planting density were promoted in the cold years of 1980 and 1981 (Fig.2). 4. The incidence of barren plant was obviously increased with increasing planting density (Table 2). It reached above 20% as NAR during the latter half of the ear-filling period decreased below 2.0g/m2/day (Fig. 4). 5. Although the highest ear DM yields were obtained at the medium planting density as 60, 000∼80, 000 plants/ha, stover DM yields and total DM yields increased with increasing planting density. Percentage of dry-matter in whole-plant did not differ significantly among planting densities in most years. Ear/Total ratio was decreased and maturity was delayed with increasing planting density (Table 3). 6. It was concluded that the optimum planting desity was about 70, 000∼75, 000 plants/ha for high yield and high quality of maize for whole-plant silage in the north-marginal area.

[学科分类] 农业科学（综合）