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- Title
Trace gas flux and the influence of short-term soil water and temperature dynamics in Australian sheep grazed pastures of differing productivity.
- Authors
Livesley, S. J.; Kiese, R.; Graham, J.; Weston, C. J.; Butterbach-Bahl, K.; Arndt, S. K.
- Abstract
Temperate pastures are often managed with P fertilizers and N2-fixing legumes to maintain and increase pasture productivity which may lead to greater nitrous oxide (N2O) emissions and reduced methane (CH4) uptake. However, the diel and inter-daily variation in N2O and CH4 flux in pastures is poorly understood, especially in relation to key environmental drivers. We investigated the effect of pasture productivity, rainfall, and changing soil moisture and temperature upon short-term soil N2O and CH4 flux dynamics during spring in sheep grazed pasture systems in southeastern Australia. N2O and CH4 flux was measured continuously in a High P (23 kg P ha−1 yr−1) and No P pasture treatment and in a sheep camp area in a Low P (4 kg P ha−1 yr−1) pasture for a four week period in spring 2005 using an automated trace gas system. Although pasture productivity was three-fold greater in the High P than No P treatment, mean CH4 uptake was similar (−6.3 ± SE 0.3 to −8.6 ± 0.4 μg C m−2 hr−1) as were mean N2O emissions (6.5 to 7.9 ± 0.8 μg N m−2 hr−1), although N2O flux in the No P pasture did not respond to changing soil water conditions. N2O emissions were greatest in the Low P sheep camp (12.4 μg ± 1.1 N m−2 hr−1) where there were also net CH4 emissions of 5.2 ± 0.5 μg C m−2 hr−1. There were significant, but weak, relationships between soil water and N2O emissions, but not between soil water and CH4 flux. The diel temperature cycle strongly influenced CH4 and N2O emissions, but this was often masked by the confounding covariate effects of changing soil water content. There were no consistently significant differences in soil mineral N or gross N transformation rates, however, measurements of substrate induced respiration (SIR) indicated that soil microbial processes in the highly productive pasture are more N limited than P limited after >20 years of P fertilizer addition. Increased productivity, through P fertilizer and legume management, did not significantly increase N2O emissions, or reduce CH4 uptake, during this 4 week measurement period, but the lack of an N2O response to rainfall in the No P pasture suggests this may be evident over a longer measurement period. This study also suggests that small compacted and nutrient enriched areas of grazed pastures may contribute greatly to the overall N2O and CH4 trace gas balance.
- Subjects
AGRICULTURE; INDUSTRIAL productivity measurement; SOIL moisture; INDUSTRIAL management; INDUSTRIAL productivity; AIR pollution; EMISSIONS (Air pollution); FORAGE plants; GRAZING; WOOL; SOIL fertility
- Publication
Plant & Soil, 2008, Vol 309, Issue 1/2, p89
- ISSN
0032-079X
- Publication type
Article
- DOI
10.1007/s11104-008-9647-8