In the semiarid regions, water and salinity stresses are increasingly becoming primary limiting environmental conditions which restrict successful establishment of crops. Sorghum is tolerant of low input levels and essentially for areas that receive too little rainfall for most other grains (Table 7). Increased demand for limited fresh water supplies, increasing use of marginal farmland, and global climatic trends, all suggest that dry land crops such as sorghum will be of growing importance to feed the world’s expanding
populations. Generally lower water demands for sorghum than maize, versus their equal ethanol yields, suggests that sorghum will be of growing importance in meeting grain-based biofuels needs. In many tropical and temperate countries where sugarcane cannot be grown, a growing interest is being focused on the potential of sweet sorghum to produce bio­ethanol feed stocks (Avant, 2008) specially that salinity and drought tolerance are major features of sweet sorghum with low water requirements for high yields. One of the main reactions to drought stress is closing of stomata. The C4 plant such as sweet sorghum, in opposite to the C3, are able to utilize very low concentration of carbon dioxide which enables them to assimilate CO2 even during considerable stomatal closure (El Bassaru, 1998). This might be one of the probable reasons for the difference in resistance to stress between both plant groups. Photosynthesis is a complex process; therefore, it is possible that a number of elements in the C3 and the C4 may differ in resistance to drought.

Sweet sorghum

About 4 months.______________

One season in temperate and two or three seasons in tropical area.

All types of drained soil.

12000 m3/h__________________

Little fertilizer required; less pest and disease complex;

easy management.____________

54 — 69 tons._________________

7 — 12%.____________________

6 — 8 tons/ha.________________

3000 L/ha.

Very simple; both manual and through mechanical harvested.

Table 7. Comparison of Sugarcane, Sugar Beet, and Sweet Sorghum in Iran (Almodares & Hadi, 2009).