Effect of transplanting time on dry matter remobilization, soluble carbohydrates and grain yield in rice (Oryza sativa L.) cultivars

To evaluate the effect of transplanting time on dry matter remobilization and grain yield of rice cultivars, a split plot arrangement in randomized complete block design was carried out with three replications in 2013 and 2014 at the College of Agriculture, University of Guilan, Rasht, Iran. The experiment consisted of six rice cultivars (Hashemi, Sangejo, Alikazemi, Dorfak, Khazar and Gouhar) and three transplanting times (05 May, 20 May and 05 June). Results showed that dry matter remobilization significantly increased from shoot to grains with delay in transplanting time. The highest dry matter remobilization was measured in Gouhar cultivar with 139.1 g.m-2 and the lowest in Hashemi, Sangejo and Alikazemi cultivars. Grain yield was positively associated with accumulated temperature and radiation. Highest accumulated temperature (1422.3 and 345.8 ˚C in whole growing and grain filling periods, respectively) were recorded in the first transplanting time. Results also showed that the Photothermal Quotient index as a ratio of radiation and temperature can be used in explantation of observed variation in grain yield of rice cultivars. Suitable transplanting time can be chosen using accumulated PTQ as different plant growth stages experienced favorable conditions of temperature and radiation (137.4 Mj.m-2.˚C for 3916.8 kg.ha-1 grain yield). In this study, transplanting on 05 May provided the favorable conditions of temperature and radiation during the vegetative and reproductive stages of rice cultivars and had positive impact on grain yield and its components.