Biochemical effects of banding limit the benefits of nitrification inhibition and controlled-release technology in the fertosphere of high N-input systems

Abstract

Enhanced efficiency fertilisers (EEFs) may have an important role in improving nitrogen (N) use efficiency in agricultural systems. The performance of EEFs when applied by broadcasting and incorporation is well documented; however, little information is available for sub-surface banded N-fertiliser. This study aimed to determine the effectiveness of EEFs within the fertosphere in several soils. This was determined by: (i) establishing the key chemical effects and N-transformation activity within a urea band, and (ii) contrasting these findings with nitrification inhibitor (NI)-coated urea and a controlled-release polymer-coated urea (PCU). A 112-day incubation experiment was conducted with the EEFs band-applied in three contrasting soils with a history of sugarcane production. In standard urea and NI-urea treated soils, the pH within the fertosphere significantly increased to a maximum of ~pH 9.2–9.3. Alkaline conditions and high ammonium concentrations promoted elevated aqueous ammonia concentrations, resulting in complete nitrification inhibition. The PCU granules released ~40% of total urea content within 14 days, followed by subsequent release at significantly lower rates. The initial rapid urea release was attributed to damaged polymer coats, while close proximity of neighbouring granules within the band may have contributed to the subsequent slower release phase through reduced concentration gradients and restricted diffusion from granules. Variation between soils suggests that soil properties such as clay content and pH buffer capacity may influence urea hydrolysis, but not nitrification. These results suggest that both NI and controlled-release technology may not have the expected impacts on N transformations and availability when applied in a concentrated band.

Modelling nitrification inhibitor effects on N<sub>2</sub>O emissions after fall- and spring-applied slurry by reducing nitrifier NH<sub>4</sub><sup>+</sup> oxidation rate

“…3.1). The use of K iNH 4 was suggested by the findings of Janke et al (2019) that NI may not have the expected impacts on N transformations and availability when applied in a concentrated band with large NH + 4 concentrations (up to 12 kg N Mg −1 ), similar to those modelled immediately after slurry application in this study. The modelled NH + 4 concentrations declined rapidly after application through diffusion, adsorption and nitrification (Sect.…”

“…These greater emissions were attributed to less NH + 4 oxidation before freezeup in fall, resulting in more NH + 4 remaining to drive NH + These model findings were consistent with field results from Chantigny et al (2017) in Quebec and Kariyapperuma et al (2012) in Ontario, where greater spring N 2 O emissions were measured when fall slurry was applied in late November than in early November. These greater spring thaw N 2 O emissions were attributed by Kariyapperuma et al (2012) to greater mineral N concentrations during spring thaw caused by less nitrification before freeze-up during the previous fall, as modelled here. The greater N 2 O emissions modelled with later slurry application were also driven by more rapid DOC oxidation from more labile manure C remaining during spring thaw.…”

“…Large N 2 O emissions measured in late winter were attributed by Dungan et al (2017) to labile N not used by soil microorganisms during the previous fall and winter that was actively metabolized when the soils began to warm in early March. Interannual differences in spring thaw emission events after fall slurry applications were related by Kariyapperuma et al (2012) to those in total soil mineral N content in the upper 15 cm of the soil profile during spring thaw. The effects of NI on N 2 O emissions during spring thaw will therefore depend on the persistence with which NI reduce nitrification in cold soils during fall and winter and thereby alter mineral N concentrations during the following spring.…”

“…where X NH 4 and X NH 4 are specific NH + 4 oxidation rates with and without NI (g N g nitrifier C −1 h −1 ), [NH + 4 ] is the aqueous NH + 4 concentration (g N m −3 in dynamic equilibrium with [NH 3 ]), and K iNH 4 is an inhibition constant set at 7000 g N m −3 to reduce inhibition at very large [NH + 4 ] as suggested in Janke et al (2019). These rates were used to calculate nitrification rates [H11]:…”

The impact of banding urea and enhanced efficiency fertilizers on nitrogen transformations and the implications for nitrogen use efficiency in high-risk environments

“…This is a method employed to reduce disturbance in soils under minimum tillage management (Busari et al, 2015) and for optimising nutrient uptake by placing the fertilizer close to the root zone, thereby limiting opportunities for losses (Sanchez et al, 1990, Sandral et al, 2017. However, banding of Nfertilizer creates a vastly different biochemical environment to broadcast and / or incorporated applications (Bezdicek et al, 1971, Hauck and Stephenson, 1965, Janke et al, 2019, with these changes possibly influencing the efficacy of various EEFs technologies. Very little research has investigated how EEFs function under banded application, leaving a significant gap in understanding on how these fertilizer products will improve NUE for a substantial proportion of global agricultural production.…”