Crop production different management factors can affect radiation (RUE) and water (WUE) use efficiency of all crops. Sowing date highly impact the final crop yield and would affect both RUE and WUE. In order to clarify the effect o sowing date on RUE and WUE of castor bean, an experiment was carried out in experimental field of Ferdowsi University of Mashhad in 2009 using three replication of complete block design. Treatment was three different sowing dates. Our results showed that by delaying the sowing date, both grain and biological yield decreased. Highest grain yield was obtained at first sowing date as 151 g m-2 which was 25 and 66 g m-2 higher that other two sowing dates. All sowing dates showed a linear relationship between incident radiation and dry biomass production. Though later sowing dates faced the crop with shorter growth duration and thus lower water consumption but WUE also decreased as sowing date delayed. There was a linear relationship between WUE and RUE.

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