Nitrous oxide emissions and herbage accumulation in smooth bromegrass pastures with nitrogen fertilizer and ruminant urine application
Nutrient Cycling in Agroecosystems(2014)
摘要
Agricultural soils contribute significantly to nitrous oxide (N 2 O) emissions, but little data is available on N 2 O emissions from smooth bromegrass ( Bromus inermis Leyss.) pastures. This study evaluated soil N 2 O emissions and herbage accumulation from smooth bromegrass pasture in eastern Nebraska, USA. Nitrous oxide emissions were measured biweekly from March to October in 2011 and 2012 using vented static chambers on smooth bromegrass plots treated with a factorial combination of five urea nitrogen (N) fertilizer rates (0, 45, 90, 135, and 180 kg ha −1 ) and two ruminant urine treatments (distilled water and urine). Urine input strongly affected daily and cumulative N 2 O emissions, but responses to N fertilizer rate depended on growing season rainfall. In 2011, when rainfall was normal, cumulative N 2 O emissions increased exponentially with N fertilizer rate. In 2012, drought reduced daily and cumulative N 2 O emission responses to N fertilizer rate. Herbage accumulation ranged from 4.46 Mg ha −1 in unfertilized pasture with distilled water to 16.01 Mg ha −1 in pasture with 180 kg N ha −1 and urine in 2011. In 2012, plots treated with urine had 2.2 times more herbage accumulation than plots treated with distilled water but showed no response to N fertilizer rate. Total applied N lost as N 2 O ranged from 0–0.6 to 0.5–1.7 % across N fertilizer rates in distilled water and urine treatments, respectively, and thus, support the Intergovernmental Panel on Climate Change default direct emission factors of 1.0 % for N fertilizer additions and 2.0 % for urine excreted by cattle on pasture.
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关键词
Climate change, Greenhouse gases, Nitrogen cycling, Pasture management, Temperate pastures
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