Sorghum is the staple crops in the Saharan areas of West Africa. Like other crops, its production is highly dependent on the improved crop seed varieties and on water use efficiency (WUE) and nitrogen use efficiency (NUE). The objective of this study was to assess the effect of sorghum root growth and water and nitrogen use efficiency on grain yield and harvest index under rainfed and drip irrigation conditions. The study was conducted in the Central region of Burkina Faso in 2014. The improved seed variety Sariaso 14 was sown. 60 kg ha-1 of nitrogen was applied. A randomized split-split-plot design with four replications was used. The results showed that the two watering systems had significant effects on sorghum WUE, NUE, root growth, grain yield and harvest index. Root growth was found to be twice higher in the rainfed condition than in the irrigation one. On the other hand, WUE and NUE were higher by 92 and 26% respectively in the irrigated plot. Irrigation was found to improve grain yield and harvest index by 44% and 56% respectively. Irrigation is considered more beneficial for farmers given the erratic distribution of rainfall.