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A 2-year field trial was conducted to study the effects of seed treatment (500 ppm) or foliar application of 1000 ppm thiourea (at 25 and 40 days after sowing) or a combination of these, on growth, yield, net photosynthesis and nitrogen metabolism of clusterbean (Cyamopsis tetragonoloba (L.) Taub.) grown for two consecutive years (1999 and 2000) under rainfed conditions of the Indian arid zone. Thiourea application either as pre-sowing seed treatment or as foliar spray significantly increased plant height, leaf area, dry matter production and seed yield as compared to the untreated control plants during both the years. However, maximum favourable effects were obtained with combined application of seed treatment and foliar spray. The beneficial effects of thiourea were attributed to its role in significantly increasing the net photosynthetic rates and the concentrations of total chlorophyll and starch in the leaves. Thiourea also reflected a positive role in enhancing nitrogen metabolism as it significantly increased nitrate reductase activity and concentration of soluble protein in the treated plants. It has been concluded that seed treatment with thiourea followed by foliar spray could significantly improve growth, yield and water use efficiency of rainfed clusterbean under arid conditions due to enhanced photosynthesis and more efficient nitrogen metabolism.