Effectiveness of Gravel Mulch and Organic Mulch in Reducing Soil Surface Evaporation and Improving Millet Yields in Yobe State, North East Nigeria

This study evaluates the effectiveness of gravel mulch and organic mulch in reducing soil surface evaporation and improving millet grain yields in the semi-arid farming zone of Yobe State, located in Nigeria's North East geopolitical zone. Water limitation is the foremost constraint on rainfed pearl millet production in Yobe State, and mulching represents a low-cost water conservation strategy available to resource-poor farmers, yet comparative data on gravel versus organic mulch performance under Sahelian conditions are absent for this zone. Using a field experiment with randomised complete block design, five mulch treatments (no mulch control, gravel mulch at 20 kg/m2, gravel mulch at 40 kg/m2, crop residue mulch at 4 tonnes/ha, and crop residue mulch at 6 tonnes/ha) were applied to millet plots over two consecutive wet seasons in Damaturu and Gujba local government areas. Soil evaporation was estimated by micro-lysimeter, soil moisture was monitored by TDR probe, and millet phenology and grain yield were recorded. Findings revealed that gravel mulch at 40 kg/m2 reduced daily soil evaporation by 62 percent compared to bare soil, exceeding the evaporation reduction of crop residue mulch (48%). However, crop residue mulch produced significantly higher millet yields (1.82 tonnes/ha) than gravel mulch (1.54 tonnes/ha) at comparable coverage levels, attributed to additional nutrient benefits from residue decomposition. The study recommends crop residue mulch retention as the priority water conservation practice for millet farmers in Yobe State, given its dual water conservation and nutrient contribution. Keywords: mulching, soil evaporation, millet, Yobe State, water conservation.