Recently, radiation technology is widely used to induce changes in plant characteristics for developing new products. So, a field experiment was carried out on alluvial clay soil at the Experimental Farm, Faculty of Agriculture, Menoufia University, Shebin El-Kom, Egypt (30.52oN and 30.99oE) during the two successive growing winter seasons, i.e. 2012/2013 and 2013/2014 on caraway plants (Carum carvi L.) to evaluate both individual and combined effects of different doses of gamma rays (0, 20, 40 and 80 Gy) and different levels of phosphorus (P) fertilizer ( 0, 50, 75, 100 and 125% of the recommended dose which are 0, 100, 150, 200 and 250 kg ordinary super phosphate/fed, respectively, P2O5=15.5 % ) on growth and yield components. The layout of this experiment was a split-plot design with the main plots that arranged in a randomized complete blocks design with three replicates.
The results revealed that irradiation by gamma rays individual and/or combined with (P) fertilizer caused significant increases in vegetative growth characters, i.e. plant height (cm), number of main branches/plant and fresh weight of whole plant (g) along with yield and oil yield parameters, i.e. number of umbels/plant, dry weight of umbels/plant (g), fruit yield (g/plant and kg/fed), volatile oil % and oil yield (cc/plant and l/fed) as well as chemical composition, i.e.photosynthetic pigments, N, P, K, crude protein and total carbohydrate contents (%) in plants. The maximum increase in the most cases of (vegetative growth characters, yield parameters and oil production) was noticed by using gamma rays at (40 Gy) combined with (P) fertilizer at (200 kg/fed).There was a gradual increase in total carbohydrate content (%) as a result of using different levels of (P) fertilizer and reached its maxima by using the interaction of gamma rays at (40 Gy) combined with (P) fertilizer at (250 kg/fed). Finally, the interaction treatments of gamma rays at the low dose (20 Gy) + each of (P) fertilization at rates of (150 or 200 kg/fed) produced the maximum content of chlorophyll a in the first and second seasons, respectively. Moreover, it could be mentioned that the highest value of chlorophyll b was happened by exposing seeds tothe moderate dose of gamma rays (40 Gy) and combined by each of (P) fertilization at (150 or 200 kg/fed) through the first and second seasons, respectively.