Low levels of phosphorus limit the yield of pearl millet (Pennisetum glaucum) grown on acid sandy soils of the West African Sahel. The application of phosphorus and the recycling of millet residues produces large increases in the total dry matter and grain yields of millet but little is known about the effects of these amendments on the by-products of millet fields which include weeds and millet leaves at harvest. Phosphorus applied at 13 kg ha−1 as single superphosphate and millet residues applied at 500 or 2000 kg ha−1 as a mulch or as the ash from 2000 kg millet residues ha−1 that had been burned, increased dry matter yields of millet leaves and weeds leading to large increments in the total in vitro metabolizable energy harvested per unit area. These increases in dry matter production were only accompanied by minor decreases in the concentration of crude protein. The increased availability of millet by-products should be taken into account when evaluating the effects of phosphorus and crop residue application on the economy and sustainability of agro-pastoral farming systems in the West African Sahel.