Effects of nitrogen and phosphorus fertilizers on growth, yield, and yield components of sorghum (Sorghum bicolor (L) Moench)

Abstract

Greenhouse and Held experiments were conducted during the 2009 and 2010 growing seasons at Botswana College of Agriculture to evaluate the effect of different levels of nitrogen (N) and phosphorus (P) fertilizers on growth, yield and yield components of sorghum. Experimental treatments for both greenhouse and field experiment consisted of factorial combinations of four rates of nitrogen (N) and four rates of phosphorus (P) making a total of 16 treatments replicated three times. The N rates in the greenhouse study were 0, 100, 200 and 400 kg N / ha whereas in the field experiment the rates were decreased to 0, 50, 100, 150 kg N / ha. Similarly the P rates for the greenhouse, study . were 0, 50, 100 and 150 kg P / ha whereas in the field the rates were decreased to 0,. 12.5, 25 and 37.5 Kg P / ha. Application rates’of 100, 200 and 400 kg N ha’ - , in ’the greenhouse significantly affected plant height, biomass, nitrogen content and protein content as compared to 0 kg N ha-1 whilst application rates of 50, 100 and 150 kg P ha’1 affected plant height, number of leaves, biomass and phosphorus content of sorghum significantly. Interaction of nitrogen and phosphorus gave significant ‘ results in plant height and biomass. From the greenhouse experiment it as was concluded that application of N and P fertilizer increase yields of sorghum. This suggest that farmers can apply fertilizer when growing sorghum.. If this research is repeated, researchers should allow sorghum to produce grain so as to find out if the yield .will be significantly different between the control, N and P application rates. In the filed experiment, N had no significant effect on grain yield, biomass, weight of 1000 seed, root weight, number of tillers per plant and flag leaf area. However, increasing N from 0 to 50 kg / ha increased grain yield, head weight and tissue N content were significantly affected by application of N. Field experiment did not produce significant results in most parameters measured. However it is recommended that the rate of 50 kg N ha-1 be recommended to farmers in their field since it increased grain yields. This research needs to be carried out in different areas of Botswana because the soil in Sebele is different from the soil in other areas of Botswana.In the field, same results were obtained with the effect of phosphorus. There were no significant effect on grain yield, biomass, weight of 1000 seed, number of tillers per plant, seed protein content, leaf nitrogen and phosphorus content. However, root weight and leaf area were significantly affected by application of P. Grain yield increased when P was increased to 25 kg/ ha therefore it is recommended that farmers should use 25 kg/ha-in their fields.