The aim of the study was to describe the distribution of pea root mass in the soil, over a three-year period, under varying weather conditions and at different levels of phosphorus application, by means of evaluating and comparing parameters of a mathematical model characterising cumulative root mass distribution. A two-factor experiment was conducted in Prusy, near Krakow: the first factor was the level of phosphorus application (0-70-140 kg P2O5 ha−1) and the second was the cultivars (six cultivars were tested). Experimental data produced using the model indicated that the root distribution was strongly differentiated by water availability in the years of the study. This appeared in some cases to be a more important factor than phosphorus application rates. The estimated soil depth at which 50% of the root mass was accumulated differed significantly for the dry and the wet year. In the wet year, only very high phosphorus application rates contributed to an increase in root mass distribution. The estimation of root mass distribution from the presented data can be used to improve phosphorus application depending on the amount of precipitation.