Abstract
We investigated features of growth and productivity in the hybrid corn, pioneer 3715, which was grown under the conditions with different combinations of plant densities, sowing times and fertilizing levels. That is, the experiment was carried out under the conditions with six plant-densities, 3,625, 5,320, 7,254, 8,866, 11,400 and 13,000 plants/10 are ; with two sowing-times, early sowing (on May 20) and late sowing (on June 20) ; and with two ways in fertilizing, namely, one is the way of fertilizing a constant amount to a plant (N, 3.4125g/plant supplied to the early sowing plots and N, 2.5594g/plant to the late sowing plots) and the other was the way of fertilizing a constant amount to an unit ground area (N, 18.0kg/10 are supplied to the early sowing plots and N, 13.6kg/10 are to the late sowing plots) (table 1). The results obtained were as follows ; 1) The aboveground yield and TDN yield had increasing tendencies with plant density rising. The highest yield was obtained under the combination of early sowing, high plant-density and heavy fertilizing (Fig.1 and Table 1). 2) Leaf Area Index riled with plant density rising (Fig.2). <LAI>^^^wholes (mean LAI over the whole growth period) obtained at the highest plant-density (13,300 plants/10 are) were 5.2 and 4.3 at the early and late sowing plots, respectively (Fig.2). The opt-<LAI>^^^whole, at which the Crop Growth Rate in the population shows the largest value, was calculated 5.78, which indicated that the aboveground yield may have increased yet even at higher plant-densities than at the highest plant-density (13,300 plants/10 are) examined in this experiment (Fig.4 and 2). 3) The <LAI>^^^mat. (mean LAI in the maturing stage) at the highest plant-density (13,300 plants/10 are) reached about 9.0 (Fig.2). The opt-LAImat. may have been calculated 6.269, which corresponded to the LAI shown at the plant density of about 8,500 plants/10 are (Fig.4 and 2). The ear yields at the early sowing plots also took the largest value around this density (Fig.1 and Table 1). 4) The aboveground yield at the late sowing plots was 35%-lower than those at the early sowing plots (Fig.1 and Table 1). The <LAI>^^^mat. at the late sowing plots reached as high value as shown at the early sowing plots, while the maturing period at the late sowing plots was considerably shortened (Fig.2 and Table 1). The yield reduction at the late sowing plots was caused by the maturing-period shortening, not by the LAI reduction. 5) The aboveground yields at the final growth-stage, as the plant density rised, increased almost in parallel with the aboveground weight at the flag leaf emergence time (regarded as the final stage of vegetative growth) (Fig.1). This phenomenon demonstrates that the aboveground weight at the flag leaf emergence time is an important determinant to the final yield and the final yield may be increased by rasing the amount of accumulation during the vegetative stage.
