Agricultural use of three (sugar-beet) vinasse composts:: effect on crops and chemical properties of a Cambisol soil in the Guadalquivir river valley (SW Spain)

Disposal of concentrated beet-vinasse, a high-density syrupy waste from the sugar industry, constituted an environmental problem. Vinasse can be recycled as a fertiliser due to its high organic matter, N, and K contents. However, the direct application of vinasse is constrained by its high salinity (EC 250-300 dS m(-1); Na 28 g kg(-1)) and high density (1.3 g cm(-3)). These problems can be overcome by co-composting the vinasse with other solid wastes. A study was conducted in the Guadalquivir river valley, SW Spain, in Coria del Rio, Seville. Three mixtures of a concentrated depotassified vinasse and solid wastes were co-composted in static windrows. The composts obtained were used in field experiments to study the effect of their application as deep fertiliser on three crops: corn (Zea mays L.); sugar-beet (Beta vulgaris L.) and sunflower (Helianthus annuus L.). The effect on chemical properties of a Xerochrept (Cambisol) soil after 2 years of compost application and after a further year of residual effect was also studied. A treatment with traditional inorganic fertiliser (applied as deep fertilisation) and an unamended soil (Control) were used for comparison purposes. Generally, the application of composts or inorganic fertiliser significantly increased crop yield when compared with the Control treatment. At the end of the experimental period, soil oxidizable-C, total humic extract-C and humic acids-C contents significantly increased in soils treated with composts when compared with Control and inorganic fertiliser treatments. Organic fertilisation also increased the Kjeldahl-N content of the soil. A slight increase of soil salinity was observed both in the composts and in the inorganic fertiliser treatments. Nevertheless, this increase did not cause sodium hazard to the soil. Go-composting of vinasse with agricultural residues serves two objectives: disposal of wastes and recycling of waste components. Furthermore, vinasse composts can be used as an alternative to mineral fertilisers. (C) 2001 Elsevier Science B.V. All rights reserved.