Exposure to moderately high levels of ionizing radiation (<20 Gy) has in some instances shown a hormetic effect in numerous vegetable-type crops. Past experiments performed in outdoor cultivars have shown a somewhat unpredictable increase in growth rate with a higher overall yield in a specified time when the seeds are exposed to ionizing radiation prior to germination. This experiment has attempted to eliminate potentially confounding variables in the growth of a legume utilizing an Environmental Protection Agency controlled green house. The experiment was a completely randomized block design with six blocks and seven treatment groups. Each treatment group of pinto beans (Phaseolus vulgaris L.) were exposed to ⁶⁰Co radiation, given doses of 5-20 Gy, planted and grown for 40 days. Due to the symbiotic relationship with rhizobium bacteria within a seed, the expected result was a lowered nitrogen fixation capacity as bacteria concentration was reduced due to sterilization by the high energy gamma, yielding a smaller plant mass. The predicted trend in reduction would be described by the linear no-threshold model. A statistically significant increase in overall plant mass occurred in the 5 Gy treatment group, with a subsequent linear trend in mass reduction at treatment levels of 7.5, 10, 12.5 and 15 Gy. The overall quality and plant mass decreased markedly at a treatment level of 20 Gy. Additional possible contributions to plant differences in growth within a green house were light intensity, temperature, CO₂ level and soil water retention. The complete randomized block design attempts to remove these as potentially confounding variables
