The influence of variability in the growth of plant root systems on plant productivity under field conditions has been difficult to evaluate. A field experiment was devised using different row spacings (101, 152 and 203 cm) to screen cotton (Gossypium hirsutum L.) germplasm for potential root growth based on the ability of an entry to explore additional soil volume for water. The basic hypothesis was that yield increases as the available soil volume increases provided a genotype has the potential to produce the root system necessary to take advantage of the additional water resources. The results show that root growth potential expressed as yield per cm row spacing (slope of the regression analyses) was significant for the entries indicating that variation exists for the rate of root growth in the germplasm. This approach offers the possibility for successfully screening germplasm for potential productivity based on diverse rooting characteristics.