Lateral roots are essential to young cotton [Gossypium hirsutum (L.)] plants for acquisition of water and nutrients. Lateral root development in the surface soil could be critical for survival of young cotton plants in semi-arid environmental conditions. On the Texas High Plains, where evaporative demand is fairly high, the more root surface area a seedling has, the greater its water absorbing capability and the less chance for growth-reducing tissue water stress to occur. Herbicides, such as trifluralin, 2,6-dinitro-N, N-dipropyl 4(Trifluoromethyl) benzen- amine and pendimethalin, N- (1-ethylpropyl)-3,4-dimethyl-2, 6 dinitrobezeneamine are commonly used to control the weeds in cotton fields. The objectives of this research were to compare the effects of pendimethalin and trifluralin on depth to first lateral root, phosphorus concentration, and lint yield of cotton under different environmental conditions. Four rates of each herbicide were used, and treatments were replicated four times. Application of trifluralin increased depth to first lateral in some treatments relative to pendimethalin. In no instances within the conditions of this study was there a significant effect of herbicide source at any rate on phosphorus concentration or final lint yield. Lateral roots are essential to young cotton [Gossypium hirsutum (L.)] plants for acquisition of water and nutrients. Lateral root development in the surface soil could be critical for survival of young cotton plants in semi-arid environmental conditions. On the Texas High Plains, where evaporative demand is fairly high, the more root surface area a seedling has, the greater its water absorbing capability and the less chance for growth-reducing tissue water stress to occur. Herbicides, such as trifluralin, 2,6-dinitro-N, N-dipropyl 4(Trifluoromethyl) benzen- amine and pendimethalin, N- (1-ethylpropyl)-3,4-dimethyl-2, 6 dinitrobezeneamine are commonly used to control the weeds in cotton fields. The objectives of this research were to compare the effects of pendimethalin and trifluralin on depth to first lateral root, phosphorus concentration, and lint yield of cotton under different environmental conditions. Four rates of each herbicide were used, and treatments were replicated four times. Application of trifluralin increased depth to first lateral in some treatments relative to pendimethalin. In no instances within the conditions of this study was there a significant effect of herbicide source at any rate on phosphorus concentration or final lint yield.