EGU2020-1763, updated on 12 Jun 2020
https://doi.org/10.5194/egusphere-egu2020-1763
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Effects of the nitrification inhibitor nitrapyrin on urea-based fertilizers in a Mediterranean calcareous soil: N dynamics and microbial functional genes.

Georgios Giannopoulos1, Lars Elsgaard2, Georgios Zanakis3, Rima B. Franklin4, Bonnie L. Brown5, and Nikolaos Barbayannis1
Georgios Giannopoulos et al.
  • 1Aristotle University of Thessaloniki, School of Agriculture, Thessaloniki, Greece (george.z.giannopoulos@gmail.com)
  • 2Department of Agroecology, Aarhus University, Tjele, Denmark (lars.elsgaard@agro.au.dk)
  • 3Pioneer Hi-Bred Hellas SA, Thessaloniki, Greece (george.zanakis@pioneer.com)
  • 4Department of Biology, Virginia Commonwealth University, Richmond, Virgninia, USA (rbfranklin@vcu.edu)
  • 5Department of Biological Sciences, University of the New Hampshire, Durham, New Hampshire, USA (bonnie.brown@unh.edu)

Nitrogen (N) fertilization is an essential agronomic practice, which increases crop yields and improves soil fertility. Globally, more than 110 x 109 kg of chemical N fertilizers are applied each year with urea-N being one of the most affordable options. Upon urea hydrolysis, any portion not assimilated by crops is either volatilized as NH3 or microbially nitrified (i.e., NH4+ oxidized) to leachable NO3- and NO2-. Nitrification inhibitors (NI) are increasingly co-applied as a sustainable agricultural practice and block the process of nitrification, resulting in a temporal increase of NH4+ in the soils. Several studies have documented the effectiveness of NIs in retaining soil NH4+ and increasing crop yields, but less is known about the effects of NIs on the fate of urea–N and the overall impact of NIs on the soil microbial community.

In a 60 day soil mesocosm experiment, we investigated the effects of Nitrapyrin (NI; 2-chloro-6-(trichloromethyl)pyridine) co-applied with a selection of urea-based fertilizers: urea (U); U with urease inhibitors (U+UI); methylene-urea (MU); and zeolite-coated urea (ZU), on a typical Mediterranean soil under ambient summer conditions. We showed that NI applied with urea fertilizers resulted in a slower decay of extractable NH4+ with a concurrent increase in NH3 volatilization. Integrated measures of soil NH4+ were 1.5 to 3.3-fold greater when NI was applied. At the same time, there was a 10 to 60% reduction in integrated measures of NO3- and NO2- when NI was applied with the tested fertilizer types, except MU fertilizer where the integrated measures of NO3- and NO2- doubled. Upon urea hydrolysis, the released NH4+ was transformed to NO3- and NO2-, which subsequently decreased in concentration following a typical nitrification - denitrification pathway in the absence of plants. Soil N2O emissions from urea fertilizers were reduced by 40% with UI, 50% with NI, and 66% with NI + UI.

Interestingly, 15 days after the application of NI, there was a decrease in bacterial abundance (eub genes; qPCR) in all fertilized treatments. NI dramatically reduced the abundance of ammonia-oxidizing microbes (amoA genes) and there were fewer bacteria associated with denitrification genes (nirK, nirS, nosZ) when NI was applied. 

At the end of the experiment, there was no significant difference in total N among all fertilized soils. Total N was in excess when compared to the control, and it was a considerable N pool potentially immobilized in microbial biomass in the absence of crops.

In conclusion, the use of NI doubled NH4+ retention in the soil and decreased soil N2O emission by 50%, through negatively affecting ammonia oxidizing and denitrifying microbes and subsequently reducing soil available NO3- and NO2-. The application of NIs should be carefully planned and synchronized (timing) with crop growth to reduce subsequent N transformations and N loss to the environment.

Keywords: urea, zeolite, methylene-urea, nitrification inhibitor, nitrapyrin, calcareous soil, soil nitrogen

How to cite: Giannopoulos, G., Elsgaard, L., Zanakis, G., B. Franklin, R., L. Brown, B., and Barbayannis, N.: Effects of the nitrification inhibitor nitrapyrin on urea-based fertilizers in a Mediterranean calcareous soil: N dynamics and microbial functional genes., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1763, https://doi.org/10.5194/egusphere-egu2020-1763, 2019

Comments on the presentation

AC: Author Comment | CC: Community Comment | Report abuse

Presentation version 1 – uploaded on 03 May 2020 , no comments