Abstract
A range of enhanced efficiency fertilizers (EEFs) have been developed in response to widespread recognition of poor nitrogen (N) use efficiency (NUE) in agriculture; however, their effective utilization is not properly understood when applied in sub-surface bands. This study quantified soil chemical changes and the distribution of N species that arose from sub-surface banding of urea, a controlled release polymer-coated urea (PCU) and urea coated with either nitrification inhibitors (NIs) or a urease inhibitor (UI), over 71 days in a field trial. Banding NIs extended the duration of nitrification inhibition for up to 50 days longer than banded urea, although the duration of NI-conferred inhibition was dependant on the rate of NI-urea application. The UI preserved urea-N at a concentration which was 16-fold higher cf. standard urea over 7 days, but no urea-N was detected after 21 days. This suggests that the NUE benefits of UIs are transient when applied in sub-surface bands. Slow release of urea-N from banded PCU resulted in lower concentrations of N in the soil solution. This reduced N dispersal by ca. 50 mm cf. urea, resulting in a N-enriched zone which was considerably smaller. Relatively benign chemical conditions around PCU bands enabled rates of nitrification (NH4–N:NO3–N ratio of 46%) which were similar to urea. Collectively, these results demonstrate the relative efficacy and risks of the different EEF technologies, when applied in fertilizer bands. This knowledge supports the effective utilization of band-applied EEFs for improved NUE in agricultural systems.
Highlights
Nitrogen (N) is frequently one of the most limiting nutrients to agricultural production, so crop responses to fertilizer-N application are often recorded
nitrification inhibitors (NIs) inhibit the oxidisation of ammonia (NH3) to nitrite (NO2-); urease inhibitors (UI) function by restricting the conversion of urea to ammonium (NH4?); and polymercoated urea (PCU) slows the release of urea into the soil solution
These technologies aim to improve the synchrony of fertilizer-N availability with plant demand by minimizing the time when N is in a form, such as nitrate (NO3–N), which is susceptible to loss from agricultural systems
Summary
Nitrogen (N) is frequently one of the most limiting nutrients to agricultural production, so crop responses to fertilizer-N application are often recorded. Inappropriate fertilizer use can lead to a leakage of N from agricultural systems through leaching, overland flow and gaseous emission This N loss may disrupt the nutrient balance and dynamics of natural ecosystems, adversely impacting inhabitants and diminishing the ability of the ecosystem to provide services (Galloway et al 2003; Hatfield and Follett 2008). NIs inhibit the oxidisation of ammonia (NH3) to nitrite (NO2-); UIs function by restricting the conversion of urea to ammonium (NH4?); and PCU slows the release of urea into the soil solution These technologies aim to improve the synchrony of fertilizer-N availability with plant demand by minimizing the time when N is in a form, such as nitrate (NO3–N), which is susceptible to loss from agricultural systems
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