MOSTAFA HOSSEINPOUR1*, SEYED HOSSEIN MAHMOODI NEZHAD DEZFULLY2 , ALIREZA PAKNEZHAD2, 1-Sugerbeet Research Department, Safi-Abad Agricultural research center, AREO, Dezful, Iran. 2- Soil and Water Research Department, Safi-Abad Agricultural research center, AREO, Dezful, Iran. 09163469321 & 09163442780. *Corresponding author Email: harm558@yahoo.com Received: 8 August 2015 Accepted: November 2015 ABSTRACT The present study investigates the radiation-use efficiency (RUE) of the autumn-sown sugar beet under variable irrigation regimes and nitrogen rates management in two independent experiments during 2009-2010 and 2010-2011at Safi-Abad Agricultural Research Center (SARC) in Dezful. The irrigation experiment includes five irrigation water levels as a ratio of plant water requirements (25%, 50%, 75%, 100% and 125%). The nitrogen experiment included five nitrogen levels (0, 60, 120, 180 and 240 KgNha-1). Both experiments were carried out using randomized complete blocks design with four replications. In both experiments intercepted radiation, leaf area index (LAI), and total dry matter were measured in two-week intervals during the growth season. Results showed no significant differences in radiation-use efficiency (RUE) under different irrigation regimes and nitrogen rates. Increased amount of water and nitrogen increased LAI. There was a 3rd degree polynomial function between the RUE and days after emergence (DAE) and between LAI and DAE. In both experiments, the peak of RUE and LAI occurred at approximately 110 and 173 DAE, respectively. Manuscript profile