Urea treatment decouples intrinsic pH control over N2O emissions in soils. (December 2021)

• Record Type: Journal Article
• Authors: Samad, Md Sainur; Ganasamurthy, Syaliny; Highton, Matthew P.; Bakken, Lars R.; Clough, Timothy J.; de Klein, Cecile A.M.; Richards, Karl G.; Lanigan, Gary J.; Morales, Sergio E.
• Is Part Of: Soil biology and biochemistry. Volume 163(2021)
• Publication Date: 2021-12
• Subjects: Denitrification -- C mineralization -- pH -- Grassland -- Nitrous oxide -- Urine patch; Soil biochemistry -- Periodicals; Soil biology -- Periodicals; Sols -- Biochimie -- Périodiques; Sols -- Biologie -- Périodiques; Sols -- Microbiologie -- Périodiques; Bodembiologie; Biochemie; 631.46
• DOI: 10.1016/j.soilbio.2021.108461
• Languages: English
• ISSNs: 0038-0717

Abstract

Abstract: Soil N2 O emission potential is commonly investigated under idealized denitrifying conditions (e.g. nitrate-N supplied and anaerobic soil), with pH commonly identified as a major determinant of N2 O emission potential. However, under urine patch conditions in grazed pastures soils a more complex series of abiotic and biotic factors may influence emissions due to the complex N transformations that occur following urea hydrolysis. These transformations may decouple native and/or expected controls of N2 O emissions encountered under classic denitrifying conditions. Here, we tracked O2, CO2, NO, N2 O and N2 emissions from urine amended soils (i.e. simulating a urine patch) to determine putative controls of N2 O emissions within 13 different pasture soils from northern (Ireland) and southern hemispheres (New Zealand). Incubations were performed under aerobic conditions±artificial urine (13.3 mg N vial −1 ) equivalent to field ruminant urine deposition rates of 1000 kg N ha −1 . Results revealed that pH was not an important regulator of the emission ratio (N2 O/(NO + N2 O + N2 )) in urine amended soils. Within urine affected soils, a new set of variables emerged as regulators of N2 O emissions, likely due to the unique environment created within this system. We show that urine results in decoupling of the initial soil pH control of the emission ratio allowing other regulators such as nitrite to dominate. In addition, we observed that the emission ratio of N2 O increased linearly with the rate of N- gas loss (NO + N2 O + N2 μmol N h −1 ), O2 consumption was positively associated with ammonia oxidising bacteria (AOB) and that the production of NO and N2 O were also enhanced under urine conditions. Highlights: Kinetic profiles reveal urine amended soils as significant sources of NO and N2 O. No relationship between soil pH and emission ratio of N2 O following urine addition. Ammonia oxidising bacterial (AOB) abundance positively correlated with oxic respiration. NO2 − was correlated with N2 O emission ratio.