Agronomic assessment of a compost consisting of seaweed and fish waste as an organic fertilizer for organic potato crops

Fish waste, seaweed and pine bark were composted to obtain a stable product rich in organic matter and nutrients for use in organic agriculture. The compost was assessed as an organic fertilizer for potato crops. The influence of three different compost rates (viz., C1 = 32 t ha(-1), C2 = 43 t ha(-1) and C3 = 65 t ha(-1)) on potato production and the chemical composition of potato tuber, petiole and foliole was compared with that of a mineral fertilizer (M), a certified organic fertilizer consisting of dehydrated broiler litter (BL) and a control treatment involving no fertilizer (C). The compost exhibited a substantial fertilizing effect and even surpassed the mineral fertilizer in this respect. The C3 treatment increased total production by 53 and 30% relative to C and M, respectively, and was similar to BL in this respect; also, it considerably reduced non-commercial production (calibre < 35 mm according to Spanish regulation RD 31/2009) relative to C. Only the C3 treatment altered the chemical composition of the tubers (specifically, it increased the content in reducing sugars). Therefore, the compost is useful as a fertilizer for organic potato crops.