Effects of Biochar, Poultry Manure and Their Combined Application on Leaf Nutrient Concentrations, Root Storage Minerals, Growth and Yield of Sweet Potato (Ipomoea Batatas L.)

Research information on the effects of biochar and poultry manure on the growth, yield and concentrations of nutrients in edible portions of sweet potato is rare, as essential nutrient concentrations in crops can affect human health. Hence, field experiments were carried out for two growing seasons (2019 and 2020) at two degraded sites using a randomized complete block design in a factorial layout with three replications to evaluate the effects of biochar (B), poultry manure (PM) and their combined application on leaf nutrient concentrations, root storage minerals, growth and yield of sweet potato. Each year, the experiment consisted of 4 × 3 factorial combinations of biochar (0, 10.0, 20.0 and 30.0 t ha-1) and poultry manure (0, 5.0 and 10.0 t ha-1). The results showed that the sole application of B and PM and their combined application, improved sweet potato leaf nutrient concentrations, root storage minerals, growth and yield of sweet potato. In both years, there were significant interactions of B and PM (B × PM) on leaf nutrient concentrations, root storage minerals, growth and yield of sweet potato that were determined, indicating the potential of B in enhancing PM use efficiency and improving better use of the nutrients in the PM. It was found that the highest application rate of 30.0 t ha-1 B and 10.0 t ha-1 PM (B30 +PM 10) gave the highest leaf nutrient concentrations, root storage minerals, growth and yield of sweet potato at both sites. Averaged over two years, the highest application rate of B at 30.0 t ha -1 and PM at 10.0 t ha-1 (B30 +PM 10) significantly increased tuber yield of sweet potato by 108, 147, 196, 89, 124 and 220%, compared with B alone at 30.0 t ha-1 (B30 +PM 10), B alone at 20.0 t ha-1 (B 20 +PM 0 ), B alone at 10.0 t ha-1 (B10 +PM0), PM alone at 10.0 t ha-1 (B30 +PM10), PM alone at 5.0 t ha-1 (B0 +PM5) and no application of B or PM (control) (B 0 +PM 0 ), respectively. Lowest leaf nutrient concentrations, root storage minerals, growth and yield was obtained for the control. The study indicated that B in combination with PM have the potential to improve sweet potato growth and yield, leaf nutrient concentrations and root storage minerals of sweet for human health in severely degraded soils. The results of this work should be verified for different soil types, crops and agroecological zones. Future research should focus on long-term field studies to fully understand the behaviour of biochar under natural circumstances. The use of variable rates of biochar, poultry manure and their combine application on should also be considered.