Effects of anaerobic digestates application on chemical composition and in vitro digestibility of alfalfa (Medicago sativa L.)

The food industry produces high quantities of organic wastes which can be used in agriculture for soil fertilization in order to reduce the application of mineral and/or synthetic fertilizers. In a permanent rain-fed meadow of alfalfa (Medicago sativa L., cv. Garisenda), the following three P fertilizer treatments were compared during the years 2006 and 2007 in a completely randomized experimental design with three replications: amendment based on the wastewater treatment of wine derived process (WWW); amendment based on wastewater from frozen food processing (WFF), an organic-mineral fertilizer (OMIN). All the treatments allowed a distribution of 75 kg ha-1 of P2O5. Three cuttings occurred: at 108, 134 and 315 days after digestates application (DAA) in 2006, and at 100, 122, and 269 DAA in 2007. Cumulative dry matter yields were measured during each experimental year. Furthermore, chemical composition and in vitro dry matter (DMD) and true DM (IVTDMD), organic matter (OMD), crude protein (CPD) and neutral detergent fibre (NDFD) digestibilities were determined. No significant difference was found among the fertilizer treatments in alfalfa cumulative dry matter yield. The fertilizer treatments affected only the hemicellulose (HC) content of alfalfa forage. Among the treatments, the WWW showed a significantly higher content of HC than WFF and OMIN. However, all digestibility parameters were unaffected by the fertilizer treatments. The results indicated that the soil distribution of these anaerobic digestates could represent a valid alternative to landfill disposal or to other waste management strategies in the mid-term period, without decreasing alfalfa yield, forage chemical composition and digestibility.