『Abstract
Urine-treated soils make a significant contribution to gaseous
N losses to the atmosphere. Our goal was to investigate the influence
of clay type and content on ammonia (NH3)
and nitrous oxide (N2O) emissions from urine
under different wetting-drying soil conditions and to relate these
results to urine-N transformation processes in soil. Three types
of silt loam soils and synthetic sand-clay aggregates with three
different clay-dominated materials (kaolinite, montmorillonite
and vermiculite) were used in this laboratory study. Bulk soil,
4-4.75 mm and 9.5-11.2 mm aggregates were incubated with synthetic
urine at 50％ and 75％ saturation under aerobic conditions. Repeated
urine application affected the properties of the aggregates depending
on the type of clay present. Greater clay content increased aggregate
stability and reduced NH3 volatilization.
The variation in clay ammonium (NH4+)
fixation capacities was reflected in NH3
volatilization as well as in the onset of N2O
emissions, occurring first kaolinite-dominated and last from vermiculite-dominated
soils. Nitrous oxide production was greater in aggregates than
in bulk soil, a difference that consistently increased with repeated
urine applications for kaolinitic and vermiculitic treatments.
A dual-peak N2O emission pattern was found,
with the second maximum increasing with the number of urine applications.
Emission of 15N-labeled N2 was
found at 75％ saturation in kaolinite and vermiculite-dominated
samples. Anaerobic conditions were less pronounced with montmorillonite-dominated
samples because shrink-swell action caused aggregate breakage.
Keywords: Greenhouse gases; Emission; Nitrogen cycle; Soil aggregates;
Clay minerals』
1. Introduction
2. Materials and methods
2.1. Soil characteristics
2.2. Urine mixtures
2.3. Synthetic aggregate properties
2.4. Incubation procedure
2.5. Analysis
2.6. Statistical analysis
3. Results
3.1. NH3 volatilization
3.2. Aggregate stability (Percentage of water stable aggregates)
3.3. N2O and N2 emissions
4. Discussion
5. Conclusions
Acknowledgments
References