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Pot experiments were conducted at the PMAS, Arid Agriculture University, Rawalpindi, Pakistan during 2007 repeated during 2008 to study the effect of silicon and nanoirrigation (W(40)) on drought tolerance mechanism of sorghum. According to experimental design, the silicon fertilization was divided into two levels: control (no application of potassium silicate) Si(0) and application of silicon Si(200) (200 mlL(-1) of potassium silicate per kg of soil). Irrigation was divided into two levels: crop upper limit (40 mm) irrigation denoted as W(40) and without irrigation, crop lower limit as Wo. Each treatment was replicated three times with two sorghum cultivars: PARC SS-2 (drought tolerant) and Johar-1(drought susceptible). The results showed that increase in silicon leads to increase in leaf area index (LAI), specific leaf weight (SLW), chlorophyll content (SPAD), leaf dry weight (LDW), shoot dry weight (SDW), root dry weight (RDW), total dry weight (TDW) and remarkably decrease in leaf water potential and shoot to root ratio in sorghum cultivars compared to control treatment. When silicon concentration is applied with irrigation LAI, SPAD, LDW, SDW, RDW, TDW, net assimilation rate (NAR), relative growth rate (RGR), leaf area ratio (LAR) and water use efficiency (WUE) increased by 30, 31, 40, 30, 28, 30, 27, 35, 32, 30 and 36% respectively as compared to water deficient treatment. These results suggest that silicon application may be useful to improve the drought tolerance of sorghum through the enhancement of water uptake ability.