The use of construction and demolition waste (CDW) and peat moss as bedding in beef cattle feedlots may affect the amount of plant-available nitrogen (N) in manure. Such an effect, however, may differ between manure from cattle fed a regular grain diet (RM) and those fed dried distiller grains with solubles (DGM). We used five 40 d crop cycles in a greenhouse bioassay to determine the effects of RM and DGM manure containing CDW or peat moss on canola (Brassica napus L.) growth and N uptake in a Black Chernozem (loam, Typic Hapocryoll) and a Brown Chernozem (sandy clay loam, Aridic Haploboroll) with or without the addition of a nitrification inhibitor (nitrapyrin) in each cycle to minimize nitrate (NO₃) leaching. Our results showed that the presence of CDW in DGM and RM manure depressed (P < 0.05) cumulative dry matter yield (CDMY) and N uptake in canola relative to manure without CDW, whereas the presence of peat increased (P < 0.05) CDMY and N uptake. Results suggest that it may be necessary to supplement CDW-amended DGM and RM manure with synthetic N fertilizer to supply adequate available N for plant uptake because the addition of CDW decreases organic N mineralization.