Harnessing microbial 'slow-release' to improve fertiliser profitability and sustainability

ADVANCES IN NITROGEN (N) fertiliser use efficiency include subsurface application and the use of enhanced efficiency fertiliser (EEF) formulations to reduce losses associated with gaseous emissions and leaching. However, results from field trials do not always show the yield increase required to cover the added cost incurred with the purchase of EEFs. Traditionally, building the soil organic N pool was the main strategy to reduce leaching losses and to better match N supply with crop demand. Nitrogen in the organic form is less prone to leaching and volatilisation, and the frequency of dry/wet cycles with the onset of summer storms stimulates N mineralisation when the crop demand for N is greatest. Results from a leaching trial using a liquid urea mono-ammonium phosphate (MAP) fertiliser indicate the inclusion of molasses in the formulation immobilised some of the N fertiliser within 10 days of application, adding to the slow-release organic N pool in the soil. Mass balance results indicate per unit of N fertiliser applied, the N supply in soil removed from leaching columns 17 weeks after liquid fertiliser application was significantly greater than the N supply in soil removed from columns fertilised with the granular product. The inclusion of molasses in the liquid fertiliser formulation provides growers with an alternative EEF, harnessing the organic slow-release capacity of soil microbes.