Re-use of sewage biosolids on canelands

This paper describes the results of field experiments which investigated the re-use of sewage biosolids on sugar cane on a Red Earth and a Yellow Podzolic soil in the Bundaberg area. Crop performance from applications of Nitram were compared with those from biosolid application rates adjusted to be equivalent to the local industry standard of 160 kg N/ha, assuming a 100%,50% or 25% availability of biosolids N. The maximum biosolids rate was 48 dry tonnes/ha. Nitrogen uptake responses occurred for both Nitram and biosolids. However, there were often no yield response to N, particularly in the first year of application due to high background soil N. At one site, yield responses were due to causes other than N nutrition. No depression in CCS was found at the highest application rates of biosolids (760 kg N/ha) and Nitram (240 kg N/ha). Estimates of the relative availability of biosolids N show they were similar in both the year of application and the year following application, with 384 and 325 kg N/ha biosolids N respectively required to achieve the same plant N uptake as that obtained from Nitram at 160 kg N/ha. Lysimeter measurements indicated the amount of nitrate N leaching was small, at least for bioso]id application rates up to 30 dry tonnes/ha. High application rates up to 48 dry tonnes/ha on the strongly acidic Yellow Podzolic soil however, showed significant increases in plant Cd, Cu and Zn concentrations. Results from these field trials provide useful indicators of the potential value of biosolius on canelands as well as highlighting some concerns which must be considered to ensure their use is environmentally acceptable.