Sufficient fertility is important for crop yield but supplying a balanced amount of each nutrient with compost is challenging and nutrient imbalances can benefit weeds more than crops. This work's goal was to partition out effects of nitrogen (N), phosphorus (P), and potassium (K) from composted poultry manure on growth of corn, lettuce, kale, and common weeds Powell amaranth, common lambsquarters, giant foxtail, and velvetleaf. Plants were grown in the field in soil amended with compost or organic single-nutrient N, P, and K amendments. P amendment as bone char did not mimic P supply from compost. Weeds responded more strongly than corn to compost. Velvetleaf response to compost appeared driven by N. Responses of other weeds and lettuce to compost were not due to N or K, and may have been driven by P or another nutrient. These results support fertility management based on soil testing and anticipated crop needs.