Emissions of nitrous oxide from runoff-irrigated and rainfed soils in semiarid north-west Kenya

Nitrous oxide is an important greenhouse gas and contributes to stratospheric ozone destruction, but still little is known about emissions of this trace gas from soils in semiarid environments and how emissions are affected by irrigation. Therefore, nitrous oxide emissions from a runoff-irrigated and rainfed endosodi-calcaric Fluvisol in the semiarid northwest of Kenya were measured using the closed chamber method. Corresponding soil moisture and nitrate contents were determined. Nitrous oxide emissions were highly correlated with soil moisture (r = 0.73, p < 0.001). The wetting of dry soil by precipitation or irrigation resulted in high emission rates of up to 0.3 g N2O-N ha(-1) h(-1). Due to excess soil moisture these rates were lower on the runoff-irrigated plots than on the rainfed ones, but decreased at an lower rate with time. Cumulative emissions for a 1-month period were similar for both treatments (55-65 g N2O-N ha(-1)). The methods applied did not allow a distinction between different sources of N2O, but considering low C and N contents of the soil and high emission rates at times of low soil nitrate content, nitrification seems to be the dominating process for the emissions observed. (C) 1999 Elsevier Science B.V. All rights reserved.