Utilization of anaerobically digested dairy slurry combined with other wastes following application to agricultural land

An anaerobic digestion method must be a powerful and useful technique to transform dairy manure into an energy source; however, the practical use of digested dairy slurry as a soil resource remains unclear. We studied on the combination of digested dairy slurry with recycled dry chemical extinguishing agents, which had been disposed of as an industrial waste but were rich in nitrogen and phosphate. We also tried to combine the digested dairy slurry with animal bone ash (hydroxyapatite), which was rich in phosphate and calcium. The supplementation of the fertilizer efficiency of dairy cattle slurry by the dissolution of the ground dry chemical agents was found to be quite effective, as it sustained yields that nearly equal or even exceeded those with the application of chemical fertilizers in the grassland. The combination of digested slurry and hydroxyapatite also led to higher yields of dent corn than the application of chemical fertilizers. The results suggested that not only the direct effects of macronutritional constituents in the digested dairy slurry as fertilizers but also the effects of other constituents as fertilizers and soil conditioners should be taken into consideration.