Paddy Rice Growing in Upland Field : The adaptability to row spacing and sowing date

Abstract

Paddy rice and upland rice (four varieties, respectively) were grown in upland field during 1958 and '59, and subjected to the following treatments: row distance of 20 or 60 cm, combined with sowing dates of 8 May or 5 June. The results obtained were as follows: (1) In the case of early sowing, the grain yields of both crops obtained from the 20 cm spacing were greater than the yields from the 60 cm spacing, but the yield increase of paddy rice caused by row distance of 20 cm as opposed to 60 cm was about 20 per cent and was greater than those of upland rice (0∼10 percent). As a result the yields of paddy rice from the 20 cm row spacing were higher than those of upland rice except the variety Norin No. 1, though the former from the 60 cm row spacing were lower than the latter except the veriety Norin No. 12. The main reason for these greater yield increase of paddy rice was the conspicuous increase of the number of ears and the straw weight per unit area, in addition the decrease of the average weight per ear was not so remarkable as that of upland rice. (2) In the case of 20 cm row spacing, the grain yield decrease of paddy rice caused by late sowing was less than that of upland rice. Therefore the yields of paddy rice were much higher than those of upland rice in the case of late sowing. This was due to the facts that the average weight per ear and accordingly the weight ratio of grain to straw of paddy rice did not decrease so markedly as that of upland rice. (3) The difference of the ratio of leaf blade to sheath is considered as one of the main factors which brought about the difference of the adaptability to the close row spacing and late sowing of these two crops. Namely, the higher ratio of leaf blade to sheath of upland rice as compared to paddy rice reduced the amount of solar radiation, lowered the temperature and raised the humidity of the air between the row more markedly under the close row spacing condition, retarding the vegetative growth of crops. (4) Though the leaf blade of upland rice was larger than that of paddy rice under the usual row spacing condition, it decreased to about the same size as that of the latter under the close row spacing, but the ratio of blade to sheath remained as high as those under the wide row spacing, or rather raised by late sowing, resulting in the remarkable reduction of the weight of leaf sheath. Therefore the yield of upland rice sown late under the closer row spacing was lower than that of paddy rice because of the small amounts of carbohydrates stored by uhe time of heading and the low photosynthetic ability after heading under the low temperature in the maturing time.