Root weight and number of nodules/seedling of Black locust (Robinia pseudoacacia L.) were differently affected by Nitrogen fertilization. Root weight was minimum in N stressed medium while number of nodules were a little less than maximum. Root weight increased significantly with 100 ppm of nitrogen while there was slight increase in nodulation. Frequent application of N resulted in increase in root weight while a reduction in the number of nodules was recorded. Phosphorus fertilization increased root weight but there was no effect on the number of nodules with phosphorus alone.