Influence of Enriched Cassava Peel Biochar and Other Soil Amendments on Growth, Yield and Proximate Composition of Sweet Potato

Sweet potato (Ipomoea batatas L.) is a vital food security crop in Nigeria and sub Saharan Africa, yet its productivity is constrained by acidic soils and declining fertility due to continuous cultivation without fertilizer inputs. Biochar has emerged as a sustainable amendment for improving soil fertility, but its slow nutrient release limits effectiveness unless combined with other inputs. This study evaluated the effects of enriched cassava peel biochar, applied alone and in combination with lime, compost, and NPK fertilizer, on the growth, yield, nutrient use efficiency, and proximate composition of sweet potato under acidic Alfisol conditions in Ibadan, Nigeria. Ten treatments were arranged in a randomized complete block design with three replicates. Growth parameters were not significantly affected (p > 0.05), but yield responses differed significantly (p < 0.05). The integrated treatment of lime + compost + biochar (T9) produced the highest tuber yield (10 t/ha), while lime + biochar (T8) yielded the greatest number of storage roots per hectare. Nutrient use efficiency indices (NUE, PUE, KUE) were markedly improved under integrated treatments, particularly T9, confirming synergistic effects of soil pH correction, organic matter enrichment, and nutrient retention. Proximate composition of tubers remained largely stable across treatments. Profitability Index analysis revealed that integrated treatments provided higher returns, with T9 achieving a profitability index of 3.51 compared to 1.63 for sole NPK (T5). These findings highlight the potential of enriched biochar, when combined with lime and compost, to sustainably improve sweet potato yield, nutrient efficiency, and farmer profitability under acidic soil conditions.