Abstract

Water stress is associated with low availability of water or with osmotic effects arising from salinity. Besides affecting crop yields, salinity may also influence biochemical composition and nutrient concentration of forage crops. To determine the effect of salinity on biochemical composition and nutrient concentration of forage sorghum [Sorghum bicolor (L.) Moench], two varieties of sorghum, Speedfeed and KFS4 were grown under rain shelter at salinity levels of 0, 5, 10, 15 dS m^-1 and irrigated when the leaf water potential reached -1 (control), -1.5 and -2 MPa. The factorial treatment combinations were arranged in a randomized complete block design with three replications. Stem dry matter, leaf dry matter and eventual dry matter yields of ratoon forage sorghum decreased with increasing salinity and irrigation interval. The reduction in plant biomass under stress conditions was found to be associated with increase in water use efficiency (WUE). Since the saline applications continued until the second harvest (first ratoon crop) as soil salinity increased, dry matter yields were reduced dramatically. No viable plants were obtained in the second ratoon crop for KFS4 variety at 15 dS m^-1 salinity and -2 MPa irrigation frequency treatments. Based on all parameters evaluated in the first ratoon crop, there was no concrete evidence to suggest that Speedfeed was superior in performance, but in the second ratoon, forage yields suggest that this variety can be a good alternative in planning for forage production.

Key words: Salinity, irrigation frequency, ratoon crop, forage sorghum.