CHEMICAL PROPERTIES AND FERTILIZER VALUE OF TEN DIFFERENT ANAEROBIC DIGESTATES.

A pot experiment was conducted to assess the fertilizer value of ten digestates obtained from typical agricultural substrates (DA), and with the addition of waste from the agri-food industry (DW). The test plant was maize. The digestates obtained from typical agricultural substrates contained more N, P and Cu, and the digestates from co-fermentation of farm residue with organic industrial waste contained more K, Mg, Ca, Zn, Fe and Mn. The heavy metals present in the digestates did not exceed (except iron) their respective amounts found in unfermented pig slurry. The maize-growing experiment proved the positive effect of digestates on maize yields, which were more than three times as high in the DAfertilized combinations (mean 377.45 g f.m./pot) and more than twice as high in the DW-fertilized combinations (mean 223.25 g f.m./pot) as in the control combination (105.25 g f.m./pot). It is concluded that the tested digestates can be recommended for agricultural use, but their fertilizer value will depend mainly on their nitrogen content. When assessing the fertilizer value of digestates, the important issue is to focus on balancing the potassium dose introduced into the soil with the digestate rather than concentrating only on nitrogen or the monitoring of heavy metals content. [ABSTRACT FROM AUTHOR]