Impact of contrasting fertilizer technologies on N dynamics from subsurface bands of “pure” or blended fertilizer applications

Abstract

Enhanced efficiency fertilizer (EEF) technologies that employ product coatings to delay nitrogen (N) release or are chemically stabilized to inhibit key steps of N transformations in soil offer potential for improving N use efficiency (NUE) in agricultural systems. However, the dynamics of N release and transformation from single technologies may result in a spatial or temporal mismatch of N supply and demand during a growing season. This may be overcome by use of blends of different technologies, provided the reduction in the concentration of stabilizing products does not reduce effectiveness. Laboratory incubations quantified the N dynamics around bands of controlled-release fertilizer (CRF) and nitrification-inhibited (NI) urea and varying blends of these technologies and referenced this against conventional urea and biodegradable, plant-oil-coated urea (POCU) applied at the same rates in two contrasting soils over 60 d. Blends of NI urea (3,4-dimethylpyrazole phosphate, DMPP urea) and a CRF (polymer-coated urea, PCU) typically resulted in N concentrations and distribution that were intermediate to those of the constituent products in unblended applications. Changes in the proportions of each product were mirrored by urea nitrogen (urea-N) concentrations around the bands in both soils, while the proportions of DMPP urea in each blend were only related to the extent of nitrification inhibition in the Vertisol. A proportion of the POCU granules burst during the early stages of incubation, resulting in initially higher mineral N concentrations compared to PCU. However, both CRFs delayed N release and formation of nitrate nitrogen (NO3-N) relative to granular urea, and mineral N distribution was similar within each soil. Soil type had a significant impact on banded N dynamics. Where there was little effect of N-fertilizer treatment on NO3-N production in the Ferralsol, the higher impedance to solute transport in the Vertisol contributed to a significant inhibitory effect of NI urea on nitrification in both pure and blended DMPP urea treatments. Using NO3-N production as a benchmark for the risk of environmental loss, the efficacy of fertilizer treatments in this soil was of DMPP urea / PCU blends (higher ratio of PCU may offer small but insignificant benefit) > DMPP urea = PCU > urea. These findings highlight the importance of soil properties in determining the N dynamics from different banded EEF products. Insights into the efficacy of biodegradable alternatives to polymer coatings and the efficacy of blended EEF products can improve the reliability of N supply while reducing environmental impacts, therefore offering greater opportunities to sustainably improve fertilizer NUE in cropping systems.