Benefits of biochar, poultry manure and biochar-poultry manure for improvement of soil properties and sweet potato productivity in degraded tropical agricultural soils

Studies on the effects of biochar and poultry manure on soil properties and sweet potato productivity are scarce. Hence, field experiments were conducted during 2019 and 2020 cropping seasons at two sites to evaluate the effects of biochar (B), poultry manure (PM) and their combined application on soil physical and chemical properties, growth and tuber yield of sweet potato (Ipomoea batatas L.). Each year, the experiment consisted of 4 x 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 experiment was laid out in a randomized complete block design with three replications. The results showed that combined application of B and PM improved soil physical and chemical properties, growth and tuber yield of sweet potato better than sole application of B and PM. In both years, there were significant interactions of B and PM (B x PM) on soil properties and sweet potato variables that were measured, indicating the potential of B in improving nutrient use efficiency of PM amendment. It was found that the highest application rate of 30.0 t ha(-1) B and 10.0 t ha(-1) PM (B-30+PM10) gave the highest tuber 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) (B-30+PM10) significantly increased tuber yield of sweet potato by 108, 147, 196, 89, 124 and 220%, compared with sole B at 30.0 t ha(-1) (B-30+PM0), sole B at 20.0 t ha(-1)(B-20+PM0), sole B at 10.0 t ha(-1) (B-10+PM0), sole PM at 10.0 t ha(-1)(B-0+PM10), sole PM at 5.0 t ha(-1)(B-0+PM5) and no application of B or PM (control) (B-0+PM0), respectively. Lowest tuber yield was obtained for the control. The multiple regressions revealed that bulk density, porosity and moisture content and soil chemical properties (pH, OC, N, P, K, Ca and Mg) significantly influenced the tuber yield of sweet potato and therefore dictated the performance of sweet potato in Alfisols of southwest Nigeria. The highest application rate of 30.0 t ha(-1) B and 10.0 t ha(-1) PM were found best on most of the measured soil physical and chemical properties, growth and tuber yield of sweet potato. The results indicated that B in combination with PM have the potential to improve soil properties and sweet potato yield of severely degraded soils.