A three-year assessment of controlled-release and nitrification-inhibiting fertilisers in the Burdekin

Abstract

The application of controlled-release and nitrification-inhibiting fertilisers may help to reduce nitrogen (N) losses from crop-root zones and enable greater plant uptake under some conditions. There have been limited research findings to date on the ability of these fertilisers to maintain production and profitability of sugarcane in field trials at N application rates lower than industry recommendations. This topic is examined drawing upon three years of harvest data (2015–2017) from 12 field trials conducted in the Burdekin. Nine of these sites tested the conventional N rate (220 kg/ha) and rates 40 kgN/ha lower than this conventional rate, for a variety of N forms. These forms were urea, a nitrification-inhibiting fertiliser and a controlled-release, polymer-coated fertiliser (CRF). The other three sites compared each product form at the conventional rate and at a rate 60 kgN/ha lower. Four sites were established on each of the three key soil types (sand, loam or clay). Fertilisers were applied at different times over the season to determine if these factors influence fertiliser efficacy. Sugarcane cultivars also varied among the trial sites. Data were analysed using restricted maximum likelihood (REML) to enable the testing of fixed effects and the allowance for random effects. Results from sites that tested N rates 40 kg/ha lower than conventional rates indicated that soil type, timing of fertiliser application and cultivar influenced the efficacy of the CRF. The CRF treatment with 50% of the N as a poly-coated urea obtained significantly higher cane yield on sandy soil, but no significant differences were identified on loam or clay soils. For fertiliser application timing, the CRF50% treatment achieved significantly higher cane yields than all other treatments, and significantly higher sugar yields than both urea treatments, when applied late in the season. Cultivar also potentially influenced fertiliser efficacy. For Q253(l), both CRF treatments (25% and 50% blends) obtained significantly higher cane and sugar yields than urea applied at a conventional N rate, but only on loam soil. This was not the case for Q183(l) on loam soil. Findings from the economic analysis indicate that the profitability of each fertiliser type varied depending on cultivar and soil type. For Q183(l) for example, CRF50% obtained significantly higher profitability than DMPP on sand, while the opposite was found on clay. The three sites testing N rates 60 kg/ha lower than conventional rate showed that the treatment effects varied depending on the cultivar and soil combinations. Annual rainfalls during the trials were below average, which may have reduced the potential efficacy of these fertilisers relative to conventional urea. © 2019 Australian Society of Sugar Cane Technologists. All rights reserved.