Nitrogen release from air-dried biosolids for fertiliser use

Mineral-N production by air-dried biosolids was measured in an Australian tenosol type soil with two moisture conditions over 70 days, using a controlled laboratory incubation procedure. The biosolids were from both air-drying pans and stockpiles. Inorganic-N components (NH(4)-N, NO(3)-N and NO(2)-N) were present in all biosolids, with higher concentrations in samples from air-drying pans compared with stockpiles of 1 yr age. Nevertheless, significant production of NO(3)-N occurred in moist soil amended with all air-dried biosolids. In contrast, saturated soil amended with air-dried biosolids generally showed a net loss of inorganic-N compounds during incubation, presumably owing to denitrification. In the saturated soil, only biosolids from air-drying pans provided NO(3)-N production from existing NH(4)-N. The results indicated that biosolids from air-drying pans provided the most robust production of NO(3)-N, compared with aged material from the stockpiles, owing to the reduced N content and increased stability of the organic fraction in stored biosolids. However, the rates of N-mineralization in the tenosol soil were substantially lower than reported for more fertile soil types and most of the organic-N content of the biosolids remained undegraded by day 70. The biosolids thus may substantially remain to provide improved properties of soil, such as structure and water-holding capacity. The results suggest that anaerobically digested biosolids from air-drying pans are potentially highly consistent products that could be effective replacements for inorganic-N fertilizer in agricultural production.