Effects of wood biochar and potassium fertilizer on soil properties, growth and yield of sweet potato ( Ipomea batata )

Studies on integrating biochar with potassium (K) fertilizer is not common. Hence, experiments were conducted in 2020 and 2021 to evaluate the sole and combined applications of biochar and K fertilizer on soil properties and performance of sweet potato. It was hypothesized that the effects of combined applications of biochar and K fertilizer on the growth, and yield of sweet potato will be more than their individual applications. The study each year consisted of a 3 × 3 factorial experiment with three levels (0, 10, and 20 t ha −1 ) of wood biochar and three levels (0, 70, and 120 kg ha −1 ) of K fertilizer (potassium chloride). The 9 treatment combinations have three replications and follow a randomized complete block design. Results revealed that biochar alone or in combination with K fertilizer improved soil physical and chemical properties, growth, and yield of sweet potato relative to the control and K fertilizer alone. The interaction of biochar and K (biochar × K fertilizer) fertilizer was significant for growth and yield parameters. The addition of K fertilizer to biochar improved the performance of sweet potato compared with sole applications of K fertilizer or biochar. 20 t ha −1 biochar +70 kg ha −1 K fertilizer and 20 t ha −1 biochar +120 kg ha −1 K fertilizer increased growth and yield relative to 10 t ha −1 biochar +70 kg ha −1 K fertilizer and 10 t ha −1 biochar +120 ha −1 kg K fertilizer. Since 20 t ha −1 biochar +120 kg ha −1 K fertilizer and 20 t ha −1 biochar +70 kg ha −1 K fertilizer were statistically similar, for this experiment, 20 t ha −1 biochar +70 kg ha −1 K fertilizer would be recommended for sweet potato production. Therefore, the addition of 70 kg K fertilizer with biochar has reduced the cost of increasing the rate to 120 kg ha −1 which would have been economical in view of the high price and lack of K fertilizer in Nigeria and other sub-Saharan African countries.