Relationship between Some Growth Indexes and Tillering of Forage Sorghum under Irrigation Regimes and Polymer

Sorghum is among the most important forages used in arid and semi-arid regions of south-eastern Iran, but its growth and yield is often constrained by water deficit and poor productivity of sandy soil. Irrigation water is becoming scarcer and more costly. The addition of water-saving superabsorbent polymer (SAP) in soil can improve soil physical properties, crop growth and yield and reduced the irriga¬tion requirement of plants. This experiment was conducted on sorghum variety ‘Speedfeed' in Zahedan, Iran during 2012 and 2013 seasons. The experimental design was a split-plot with two factors including four irrigation regime (providing 55, 70, 85 and 100% from consumptive (ET crop) of sorghum) as main plots and four amounts of SAP (0, 40, 80 and 120 kg ha-1) as subplots in a completely randomized block design with three replications. Irrigation level and SAP had significant effects on leaf area index, crop growth rate, leaf area duration and number of tillers per plant. Water stress decreased leaf area index, leaf area duration, crop growth rate and tillers per plant. Our results have shown that the applied SAP had an important effect on forage sorghum and increased leaf area index, leaf area duration, crop growth rate and tillers per plant. The results indicated with an increase in the LAI, LAD and CGR the number of tillers per plant increases.