抄録
Starch produced and accumulated in the straw particularly in leaf sheath and culm by the heading time is translocated into the growing dars after heading. Thus at 20∼25 days after heading starch content in the straw decreases to almost trace. In the following period starch accumulates again in the straw vainly. It is caused by the excessive production of starch by photosynthesis beyond the sufficient amount of starch required to grain development. In the control plots, amount of starch accumulated in the straw by the heading time and that accumulated again at the later stage of ripening vary with the different condition of nitrogen supply, indicating the balance between the number of spikelets and the quantity of starch produced, ie, the balance between the number of vessels and the quantity of substance to be delivered into them. Thus, in the plot B, starch production is less in relative proportion to the greatest number of spikelets formed due to high nitrogen level, and consequently the reaccumulation of starch is the least. On the contrary in plot C, being supplied with nitrogen top-dressing at the heading time, starch production is excessive in proportion to the number of spikelets and starch is stored in the straw vainly, because nitrogen supplied at the heading time has no effect in increasing the number of spikelets but is very effective in promoting photosynthetic production during the period after heading (fig. 2 and 3). The balance mentioned above determines the seed-setting percentage as well as the weight of grains (fig. 4). In the shaded plot, starch contained in the straw before heading is exhausted more rapidly than that of control plots and no further accumulation takes place. Translocation of carbohydrates from the straw to the ears is recognized not inhibited by the shading treatment. The seed-setting rate and weight of grains in the shaded plots are lower than these of the control plots. The difference in the seed-setting rate and weight of grains is caused mainly by the difference in these characters of spikelets located on the secondary rachis-branches, ie, the spikelets on the secondary rachis-branches, excluding spikelets at the top of the branches, are very changeable in these characters and are very influential in determining these characters as a whole ear (fig. 5). Content of nitrogen, phosphorus and potassium in the plant as well as the total amount per hill of these nutrients are determined with the control plot and the shaded plot in plot A. It is shown that the shading treatment inhibits remarkably not only the absorption of phosphorus but also the teanslocation of this element from the straw to the ears, whereas there is no such a change with nitrogen and potassium (fig. 7 and 8).
