Residual Effects of Sawdust and Poultry Manure Biochars on Soil Chemical Properties and Vegetative Growth of Maize in Degraded Soils of Southwestern Nigeria

Soil fertility decline remains a major limitation to maize productivity in sub-Saharan Africa, where restricted access to fertilizers constrains efforts to close yield gaps. Sustainable soil management strategies that enhance residual nutrient availability are therefore critical for maintaining crop performance under low-input conditions. This study assessed the residual effects of sawdust biochar (SB) and poultry manure biochar (PB), applied singly and in combination at 0.5%, 1%, and 1.5% (w/w) in a preceding experiment, on soil chemical properties and maize growth under screenhouse conditions. The experiment comprised 40 pots arranged in a completely randomized design with 10 treatments replicated four times, and was conducted for eight weeks in the Department of Agronomy, University of Ibadan. The results showed that the residual effect of biochar treatments significantly enhanced maize growth, assessed via standardized vegetative growth indices and dry matter accumulation. Poultry manure biochar (PB) at 1.5% produced the highest growth index and dry matter yield, corresponding to increases of 32% and 156% relative to the control. Similarly, at harvest, soil nutrient contents (p < 0.05) remained significantly higher under PB and SB treatments, although total nitrogen remained the major limiting factor. These findings indicate that residual biochar can sustain soil fertility and improve maize growth, but require complementary N inputs for maximum benefits. For smallholder farmers managing highly degraded soils in Nigeria, integrating biochar with modest fertilizer use offers a pathway to restore soil fertility and support crop productivity under low-input conditions.