Effect of sowing date on grain quality of sorghum (Sorghum bicolor L. moench) in the Nile corridor agroecological zone of South Sudan

Sorghum (Sorghum bicolor (L.) Moench) is a staple food for a considerable number of people in Africa and Asia. However, poor grain quality is a major concern for the rural communities who depend mainly on sorghum grain for food. Protein, minerals and tannins are important indicators of grain quality. Their quantity is critical in choice of variety to grow for food. An experiment was carried out in a randomised complete block design by sowing 5 sorghum varieties on 18 th June, 29 th June and 10 th July 2015in Bor and Arek South Sudan. The objective of the study was to determine the effect of sowing date on protein, tannins, iron and zinc content in sorghum. Grain samples of five sorghum varieties sown on various dates were collected and analysed at Kenya Agricultural and Livestock Research Organization (KALRO) Njoro. Protein content was determined using method 44 from Association of American Cereal Chemists. Tannins were determined using the Improved Vanillin-Hydrochloric Acid Assay (IVHAA) while minerals; iron and zinc were determined using Atomic Absorption Spectrophotometry. Significant site by variety by sowing date interactions at P < 0.05 level of probability were obtained for protein, iron and zinc content of sorghum varieties but not for tannins. Highest protein content of 11.55 per cent was achieved when varieties were sown on 29 th June in Bor. Protein of 11.40 per cent was obtained when varieties were sown on 18 th June in Arek. At Bor, Beer, Dhet and Seredo varieties; 12.76, 11.0 and 10.64 per cent protein respectively were recorded. At Arek, Beer Seredo and Dhet attained 12.03, 10.92 and 10.60 per cent protein content respectively. Sorghum varieties sown on 18 th June had less tannins of 1.19 mgml -1 in Bor and 1.09 mgml -1 in Arek while varieties sown on 10 th July had highest tannins 1.49 mgml -1 in Bor and 1.40 mgml -1 in Arek. Amongst the varieties, Seredo and Agany contained high tannins while Beer and Dhet contained less tannins. Iron and zinc content in sorghum showed higher values for 29 th June sowing date both in Bor and Arek. The study showed that Beer and Dhet varieties have good quality grains that can be used to improve human nutrition, hence can be recommended to sorghum farmers in Bor and Arek region.