Studies on the Growth and Productivity of Maize for Whole-Plant Silage in the North-Marginal Area, Nemuro District in Hokkaido : II. Dry-matter accumulation habits and climatic factors.

Abstract

The object of this report is to clarify the dry-matter accumulation habits and to investigate the effects of climatic factors on the dry-matter production and yield of maize for whole-plant silage in the north-marginal area in Japan. Experiments were repeated in the same method except variety and planting date over 6 years (1976∼'81). Heigen-wase (early hybrid) was used over a 3-year period (1976∼'78), and Wase-homare(early hybrid) was used over a 4-year period (1978∼'81). Both varieties were planted on 4 or 3 different dates from mid-May in each year. The dry-matter weight in each organ was measured at 3-week intervals, from 6 weeks before silking date, and dry-matter yields were measured at harvesting date. The results obtained were as follows: 1. The dry weight of leaf blade showed little variation during the ear-filling period. The dry weight of stem (culm+leaf sheath+tassel) increased slowly during the first half of the ear-filling period and then showed increase or decrease during the latter half of the ear-filling period. The dry weight of ear )kernel+cov+husk) increased linearly, and showed extremely large differences among years. The dry weight of top was affected remarkably by the weight of ear, which resulted in large differences among years in the dry weight of top (Fig. 2 and Fig. 3). 2. Top dry weight growth rate (CGR) changed like a shape of unimodal curve with a peak value occurring at about silking in each year, and showed a rapid decrease during the ear-filling period. Net assimilation rate(NAR) showed a tendency to have a maximum value during the period of 3 weeks before silking. Leaf area index (LAI) reached a maximum at silking or 3 weeks after silking and then decreased gradually (Fig. 4). 3. CGR in each growth period indicated highly positive correlation with different growth parameters: with LAI during the period of 6∼3 weeks before silking, with NAR during the period of 3 weeks before silking (period II) and the first half of the ear-filling period (period III), and with both of NAR and LAI during the latter half of the ear-filling period (period IV), respectively (Table 1). 4. CGR in the period II positively correlated with temperature of daily mean, maximum and minimum, and sunshine hours, but negatively correlated with rainfall. CGR in the period III and IV indicated highly positive correlation with the three temperature factors described above, sunshine hours and solar radiation, and indicated the highest positive correlation with daily maximum temperature. But CGR in the period IV indicated negative correlation with daily mean wind speed (Table 2). 5. Stover DM yield indicated positive correlation with CGR in the period II. Ear DM yield indicated highly positive correlation with CGR in the period III and IV. Although total DM yield was affected by the ear ratio, total DM yield indicated the highest positive correlation with CGR in the period III and IV. Both of percentages of dry-matter in ear and whole-plant, and ear/total ratio indicated highly positive correlation with CGR in later growth period. CGR during the latter half of the ear-filling period showed the greatest influence on yield and quality of maize for whole-plant silage (Table 4). 6. From above results, it was concluded that increase of CGR during the latter half of the ear-filling period was essential for stable and high yield and quality of maize for whole-plant silage under severe conditions in the north-marginal area.