Abstract
This paper dealt with the increment of silage corn production in Hokkaido, the northernmost main island in Japan, with the high plant-density cultivation. Two hybrids, Caldera 535 (early maturity) and Pioneer 3715 (late maturity), were used as experimental materials. Both hybrids were grown at different thirteen plant-densities ranging from 2,850 plants/10 are up to 19,950 plants/10 are so as to investigate the effects of plant density on the yield and the characters related to the yield. The different plant densities were obtained by changing the inter-row width from 20cm to 140cm with increments of 10cm. While the inter-plant space within each row was constant (25cm). The amount of fertilizer supplied to a plant was constant, N, 3.16g ; P_2O_5, 6.85g ; K_2O, 3.16g (at 6,000 plants/10 are, for example, N supplied was 19kg/10 are). The results obtained were as follows ; 1) The aboveground (stover+ear) weight per plant in both hybrids reduced exponentially with plant density rising, substantially leveling off at the density over 15,000 plants/10 are. The reduction in the ear weight per plant with plant density rising was much more outstanding than that in the aboveground weight (Fig.2). The ear capacity, l×a×b (l, ear length ; a and b, long and short diameters corssing rectangularly at the largest part of ear) decreased with plant density rising, and the decreasing tendency was shown more markedly in Pioneer 3715 than in Caldera 535 (Fig.4). 2) The aboveground yield per unit ground area considerably increased with plant density rising in both hybrids. The ear yield per unit ground area also increased a little with plant density rising. The ear ratio (ear weight/aboveground weight) decreased with plant density rising (Fig.3). 3) The leaf area index (LAI) increased linearly with plant density rising (Fig.5). Since at high densities SLA (Specific Leaf Area, Leaf area per unit leaf weight) increased in both hybrids (Fig.7), high-density populations may have had a large leaf area for the leaf weight of the population. 4) The maximum LAIs at the plant density of 6,000 plants/10 are, which is a standard density of corn cultivation in Hokkaido, showed about 3.0 and 4.5 for Caldera 535 and Pioneer 3715, respectively. The light extenction coefficient (k) of corn populations were 0.55 and 0.45 for Caldera 535 and Pioneer 3715, respectively (Fig.6). The ratios of light interception by plants at the density of 6,000 plants/10 are were 80% and 87% for Caldera 535 (LAI=3.0, k=0.55) and for Pioneer 3715 (LAI=4.5, k=0.45), respectively (Fig.6). Considerably much light (20% and 13% to the incident light) was permitted to pass through without being received, as photosynthetic energy, by leaves. To raise the light utilization efficiency (up to 95% light interception) it was necessary that the plant density of both bybrids should be raised up to 10,000 plants/10 are. 5) Judging from the results obtained in the experiment, the standard plant-density (6,000 plants/10 are) recommended in Hokkaido may be regarded as a little too low. The higher production of silage corn should be expected by raising the plant density up to nearly 10,000 plants/10 are, especially in the central and south-western part of Hokkaido where the corn plant may have a comparably good growth.
