This dataset contains nitrogen data from nitrate, ammonium and nitrite, total nitrogen and carbon data, and elemental composition data from anaerobic digestate and biomass ash from UK bioenergy production. Anaerobic digestate was sampled 8 times from different industrial scale plants across the UK between January 2015 and January 2018 and biomass ash was sampled in January 2015 and June 2016. Anaerobic digestate was sourced from segregated food waste (mainly household waste), pig slurry, maize silage, vegetables waste, sweet corn waste, aerobically treated food waste, food manufacturer waste and other biodegradable sludge from within the UK. Biomass ash, both fly and bottom ash, from virgin and recycled wood was sourced from three sites within the UK and one from Spain. All laboratory analyses were undertaken at Lancaster University using standardised methods. The data were collected as part of the research grant, Developing a suite of novel land conditioners and plant fertilizers from the waste streams of biomass energy generation. The research was funded by NERC, award NE/L014122/1.