Analysis of the mechanism of low-yielding of rice crop caused by late transplanting : (IV) On the yielding responses of seeding sown at different densities in nursery and transplanted lately to paddy field

摘要

1.In the previous experiment, it was shown that the late transplanting of rice results in a remarkable decrease of yields, particularly when the seeds are sown densely in the nursery, and thinner seeding seems to be able to raise seedlings to produce higher yield, even when they are transplanted later than usual. 2. With the aim to analyze the low yields caused by late transplanting, wa have compared the growth and yield of rice plarnts sown at four different densities in the nursery ; i. e. 541cc, 180cc, 45cc and 18cc of seeds were sown respectively per 3.3m2. Seedlings thus obtained were transplanted under the same density ; 90 hills per 3.3m2 (24.2cm×15.2cm) of paddy field. 3. Yields of the plants transplanted 30 days later when compared with the control are as follows : (i) Plot sown at the density of 541cc per 3.3m2 gives only three quarters of the yield of the control culture. (ii) Sparsely sown plot (180cc, 54cc and 18cc plot) showed nearly the same or even larger yields than that of the control. 4. The high yields obtained in the sparsely sown plots may be explained as follows : (i) As the seedlings had good enough space to grow in the nursery, they could produce many healthy tillers on the lower nodes by the time of transplanting (July 5).(ii) Consequently the larger number of tillers and ears were obtained from lower nodes.(iii) As tillers from the lower node start early in growth, and their heading take place also early, In such a case even the tillers produced from upper nodes on late transplanting, ded not so much delay in heading (iv) The reduction in grain weight, grain numbers per ear, and fertility were compensated by the increased number of stems. 5. The low yield of the 541cc plot may be explained as follows : (i) Many of the main stems died prematurely. (ii) Tillers have appeared from the upper nodes. (iii) As tillering delayed, heading also became late, fertility, decreased and reduced weight of grains resulted. (iv) Although the number of stems or ears were equal to that of usual culture it, could not overcome the seriously decreased weight of each ears, in this case.