Why benefits from controlled release fertilisers can be lower than expected on some soils

CONTROLLED RELEASE FERTILISERS (CRFs) have received increased interest by the Australian sugarcane industry as part of efforts to evaluate the use of enhanced efficiency fertilisers to reduce nitrogen (N) losses and improve N use efficiency. Experimental results and simulations, here and abroad, have shown that benefits from CRFs are dependent on soil and management conditions and are highly seasonally variable. Understanding the causes of this variability may better define where and when benefits can be expected from the use of CRFs. Here we use simulation analysis to quantify and explain the effects of soil type on agronomic and environmental benefits from CRF use for a case study in Tully, Queensland. The simulation results indicate that CRFs can reduce N loss via both denitrification and deep drainage (leaching). The reduced N losses do, however, not always translate into agronomic benefits, these being an increase in yield and/or a decrease in the optimal rate of N. Agronomic benefits are dependent on the inherent N responsiveness of the system and the seasonal yield potential. For example, on some soils the conditions that give rise to large N losses (e.g. prolonged waterlogging) can also limit crop growth and yield potential. As a consequence the agronomic benefits from CRF may not always be realized on these soils and even some of the environmental benefits may be transient.