Effect of Combined Application of NPK Fertilizer and Poultry Manure on the Nutritional and Functional Properties of Aerial Yam (Dioscorea bulbifera)

Aims: To investigate the effects of combined application of NPK fertilizer and poultry manure on the nutrient composition and functional properties of flours from aerial yam (Dioscorea bulbifera).
Study Design: The experiment was a single factor trial in a randomized complete block design replicated three times.
Place and Duration of Study: National Root Crops Research Institute, Umudike Research farm in 2012 and 2013 cropping seasons.
Methodology: The treatment combinations consisted of four levels (150, 250, 350 and 450kg/ha) of NPK 15:15:15 fertilizer and four levels (1, 2, 3, 4t/ha) of poultry manure with a control (No fertilizer or manure application). After harvest the bulbils were analysed for starch yield, proximate composition (dry matter, crude protein, ash, crude fibre, crude fat), total carotenoid and mineral (phosphorus, calcium and magnesium) contents. The functional properties of the flour were also investigated.
Results: Starch content increased significantly from 8.52% in the control to 14.95% in 450:1 NPK and poultry manure, ash content increased from 3.73% in control to 6.58% in 350:1 and 450:1 NPK and poultry manure. Crude protein increased from 1.35% in control to 4.33% in 350:2NPK and poultry manure. However the dry matter content decreased from 31.06% in the control to 22.28% in 250:1 NPK and poultry manure. Gelatinization temperature increased from 74ºC in the control to 88.50ºC in 450:2 NPK and poultry manure. Bulk density was not significantly affected by NPK and poultry manure, however, swelling index reduced from 200.16 in the control to 80.50 in 350:4 NPK and poultry manure.
Conclusion: Combined application of NPK and poultry manure may increase some nutrients in Dioscorea bulbifera however some important functional properties of the flours were adversely affected which may have effect on its utilization.