Studies on the lodging of rice plant (4)

Abstract

This study was undertaken to analyze the effect of rain, especially rain water deposition on rice lodging. Paddy rice, Norin No. 29 cultured in pots was used for the experiment. At different stages of ripening in 1962 and 1963, the plants were exposed for a day to a drizzle of artificial rain from spray nozzles connected with a water tap. Several factors of the plants related to lodging were measured before and after the treatment and the following results were obtaind. 1) In general, weight of the aerial part of the plants increased about 30 to 60 per cent (2.6 to 4.3 gr.) by rain treatment. The increment in weight varied with condition of wetting and ripening stage. In the plant under calm conditions and with a maximum amount of rain water deposited on their body, the increment was about 20 per cent higher than that of the plant on which the rain was shaken off as under the windy conditions. The increment was also about 10 per cent higher in the plant at full ripening stage than that in the plant at dough stage. 2) The remarkable increase in weight was recognized in leaf blade and culm with leaf sheath, but was not so in a head part. Difference between the maximum and the minimum weight due to wetting was largest in the leaf blade and smallest in the culm with leaf sheath. 3) Height of the center of gravity of the plants was lowered by 2 to 5 per cent of the standard plants, so it is thought that the lowering of the center of the gravity gives little effect on the lodging. 4) Bending momemt caused by the weight of the plant had been calculated from the data of bulk weight and height of center of gravity. The moment increased from a little more than 20 to 50 per cent and the moment of the plants with maximum rain water deposition were about 20 per cent higher than that in the plants with minimum rain water deposition by waving. 5) When the plant was exposed to rain, breaking strength of the culm with leaf sheath in the 4th and 3rd internodes showed an increasing tendency. It is thought that a relation exists between the increase of expansion pressure in the cells of the culm and leaf sheath due to decreasing transpiration resulting from the plant being under an almost saturated atmosphere and wetting the plant surface. However, a significant difference in the strength was not recognized as affected by probable increase in the friction resistance between culm and leaf sheath. From the above results, the increment of bending moment based on the plant weight is the most important factor increasing the lodging of rice plants by rain. The moment has a closer connection with increasing weight of a plant body than the changing height of the center of gravity of the plant. © 1966, The Society of Agricultural Meteorology of Japan. All rights reserved.