We assessed the effectiveness use of the new NKSMg fertilizer on the germination of rapeseed (Brassica napus L. var. napus). The fertilizer was produced on the basis of protein hydrolysate from processing of poultry feathers. The whole process is based on the digestion of feather waste by acidic hydrolysis, adjusting pH of the reaction medium, and then enriched in select nutrients. The method allows the production of liquid fertilizers that can be used in soil and foliar applications. Pot experiments have shown that the use of NKSMg fertilizer based on protein hydrolysate of keratin had a significant effect on the increase of plant biomass. The contents of nitrogen, phosphorus, potassium, and magnesium in plants increased by 76.2, 5.20, 37.3, and 29.6%, respectively, compared to unfertilized plants. The use of fertilizer also significantly modified the contents of manganese and zinc in tested plants. Technology of production of fertilizers based on protein hydrolysate is currently implemented by Intermag Co., Polish leader in the manufacture of fertilizers, growth stimulators, and other preparations designed for professional agriculture and horticulture.