The high rice grain yields ensured by sprinkler irrigation have encouraged the use of higher fertilizer doses, mainly the nitrogen fertilizers. However, an improper management of nitrogen fertilization may result in plant lodging. Application of plant regulators may redirect assimilates to grain production while limiting the vegetative growth. This study aimed to: evaluate the influence of the growth regulator Ethyl-trinexapac on plant growth parameters and on 15N accumulation and distribution in the whole plant and plant components, and determine the contribution of nitrogen taken up in different developmental stages in panicle formation, yield components and rice yield. The experiment was carried out under controlled greenhouse conditions. The treatments consisted of application or not of a plant growth regulator (0 and 200 g active ingredient ha-1 of ethyl-trinexapac) at four plant development stages (1 - beginning to end of tillering; 2 - end of tillering and flower differentiation; 3 - flower differentiation to flowering; 4 - flowering until physiological maturation). The experimental design was arranged in random blocks, in a 2 x 4 factorial scheme, with three replications. The plants were placed in a group of 48 pots. In a group of 24 pots with nutrient solution containing 15NH4SO4, plants were collected and separated in parts in the beginning of each pre-established plant development stage and at the end of each stage. In a second group (24 pots), pre-labeled plants were left to grow in nutrient solution with 14NH4SO4 and harvested at the end of each cycle in order to access 15N redistribution.. The growth regulator reduced plant height and 15N accumulation in the panicle and promoted redistribution of the absorbed 15N, and increased accumulated 15N in root, stem+sheats and leaves. The contribution of absorbed 15N to panicle formation in each stage increased with the plant development, though in a lower proportion in the presence of the growth regulator. Ethyl-trinexapac influenced components and rice yield negatively.
dry matter accumulation; Oryza sativa L.; plant growth regulator; plant height
