The effect of soil texture and soil drainage on emissions of nitric oxide and nitrous oxide

Agricultural soils are important sources of the tropospheric ozone precursor NO and the greenhouse gas N2O. Emissions are controlled primarily by parameters that vary the soil mineral N supply, temperature and soil aeration. In this field experiment, the importance of soil physical properties on emissions of NO and N2O are identified. Fluxes were measured from 13 soils which belonged to 11 different soil series, ranging from poorly drained silty clay loams to freely drained sandy loams. All soils were under the same soil management regime and crop type (winter barley) and in the same maritime climate zone. Despite this, emissions of NO and N2O ranged over two orders of magnitude on all three measurement occasions, in spring before and after fertilizer application, and in autumn after harvest. NO emissions ranged from 0.3 to 215 mug NO-N m(-2) h(-1), with maximum emissions always from the most sandy, freely drained soil. Nitrous oxide emissions ranged from 0 to 193 mug N2O-N m(-2) h(-1). Seasonal shifts in soil aeration caused maximum N2O emissions to switch from freely drained sandy soils in spring to imperfectly drained soils with high clay contents in autumn. Although effects of soil type on emissions were not consistent, N2O emission was best related to a combination of bulk density and clay content and the NO/N2O ratio decreased logarithmically with increasing water filled pore space.