Effects of NPK compound fertilizer and harvesting stages on growth and grain yield parameters of sweet sorghum [Sorghum bicolor (L.) Moench]
In Botswana, sweet sorghum is a popular snack crop which is grown with no fertilizer application. Also the time it is harvested is very early resulting in very low seed production of poor quality as most of it has not matured. The study was conducted in Francistown, Botswana during 2010-2011 in order to determine the NPK compound fertilizer requirement and harvesting stage which may improve growth and grain yield of sweet sorghum. Six NPK compound fertilizer 2:3:2 (22) levels were used: Control, 400, 800, 1200, 1600 and 2000 kg ha-1. There were two harvesting stages, soft dough (H1) and physiological maturity (H2). The experiment was a split-plot design with four replications. Fertilizer levels formed the main plots while the two harvesting stages formed sub-plots. Results indicated that different levels of fertilizer significantly (p< 0.01) increased growth (stalk diameter, panicle dry weight and total dry weight). Stalk height was also significantly (p< 0.05) increased, while 1000 grain weight was significantly (p< 0.05) increased by 18 to 23%. Fertilizer levels 800-2000kg ha-1 significantly (p<0.01) increased grain yield by 73 to 110% compared to the control. Grain yield at H2 stage was 83 % higher than H1 stage. The results seem to indicate that an NPK compound fertilizer level not exceeding 800 kg ha-1 (50:75:50 kg NPK ha-1) and harvesting at physiological maturity (H2) could be recommended.
Key words: sweet sorghum, NPK compound fertilizer, growth, harvest stage, grain yield, rain-fed production, Botswana
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