Morphological responses of forage sorghums to salinity and irrigation frequency

Abstract

Water stress occurs when the demand for water exceeds the available amount during a certain period or when 
poor quality water restricts its use. In particular, water stress is associated with low availability of water, as well 
as osmotic effects associated with salinity. The response of forage sorghum [Sorghum bicolor (L.) Moench] 
varieties to salinity and irrigation frequency were studied from December 2007 to December 2009. Two forage 
sorghum varieties (Speedfeed and KFS4) were grown under salinity levels of 0, 5, 10 and 15 dS m-1 and irrigated 
when the leaf water potential reached -1.0 (control), -1.5 and -2.0 MPa. Irrigation frequency and salinity were 
found to affect the morphology and growth of the forage sorghum. Maximum number of leaves was produced in 
non-saline soil (13.5 leaves plant-1) with normal irrigation (12.4 leaves plant-1). Low soil water and high salinity 
reduced the number of leaves as well as the number of tillers produced. Leaf area of plants were also reduced in 
response to salinity and decreasing soil water availability, while the suppressive effect was magnified under the 
combined effect of the two factors. Significant differences in stem diameter were found between the frequently 
and the least frequently watered plants, and stem diameter decreased with increasing salinity. Leaf firing 
increased with increasing salinity reaching 59.9% in the extreme salinity treatment of 15 dS m-1, and it increased 
with increasing water stress reaching 48.6% in the extreme water stress treatment of -2 MPa. Under stress 
condition, the KFS4 variety had a better performance in terms of morphological and growth parameters 
compared to Speedfeed variety. The threshold concentration was found to vary with variety. However, in control 
treatment, Speedfeed variety had greater leaf area, plant heights, number of leaf and number of tiller.