Can zeolites be used in sugarcane cropping systems to help reduce nitrogen losses into the Australian Great Barrier Reef?

Aims: The aim of this study was to determine the effectiveness of natural (NatZeo) and acid-treated (AcidZeo) zeolites in increasing the nitrogen (N) recovery of sugarcane grown under conditions highly conducive for N losses. Methods: This glasshouse trial replicated the pedoclimatic conditions typical of the Australian sugarcane industry in the Wet Tropics to evaluate the capacity and economic feasibility of using NatZeo and AcidZeo to reduce leaching and increase plant and soil N recovery in a highly permeable sandy-loam soil. Nitrogen fertiliser was applied at two rates (84 and 120 kg N ha⁻¹) as ¹⁵N-enriched urea. Results: Compared with the unamended treatments, AcidZeo led to significantly higher average fertiliser N recoveries in both the soil (+24%) and plant (+54%), which resulted in significantly lower overall N losses (−22%). However, the significantly higher capacity of AcidZeo in retaining ions limited the availability of potassium and sulphur to the plants and led to a 4% yield reduction. The use of NatZeo led to lower abatements of N losses (−6%) but increased N recoveries in the plant (+22%). NatZeo did not result in as much cation immobilisation, which, combined with the increased plant/soil N recovery, resulted in the highest yield of the trial (+8% compared with the unamended treatments). The economic analysis indicated that only NatZeo could potentially increase farmer’s income when applied in 20 cm wide strips around the fertiliser band. Conclusions: This study highlights that zeolites have potential to improve the environmental sustainability and profitability of sugarcane cropping systems.