Soil tillage enhanced CO2 and N2O emissions from loamy sand soil under spring barley

Soil tillage intensity can be expected to affect the greenhouse gas balance of arable cropping systems through effects on soil physics and biology affecting soil carbon storage and nitrous oxide (N2O) emissions. The effects of conventional tillage (CT) with ploughing to 20 cm, reduced tillage (RT) with harrowing to 8-10 cm and direct drilling (DD) on CO2 and N2O emissions from a loamy sand soil (8.1% clay, 3.5% organic matter) under spring barley undersown with ryegrass were measured by static chambers over a period of H 3 days in spring and summer 2004 in a tillage experiment established in 2002 at Foulum, Denmark. There was a high temporal and spatial variation in both CO2 and N2O emissions, which made the comparisons of treatment effects on emissions on single dates difficult. However, this variation was reduced when the measurements were corrected for diurnal variation in the emissions and when emissions were cumulated over a longer period. Both CO2 and N2O emissions decreased in the order CT > RT > DD. Compared with CT (40 kg C day(-1)) the cumulated CO2 emissions during the 91 days after tillage were 21 and 25% lower for the RT and the DD treatments, respectively. The cumulated N2O emission from CT over the entire observation period (0.89 kg N ha(-1) or 7.9 g N day(-1)) was about twice that of DD. The N2O emissions were significantly higher for CT compared with DD and RT, even before tillage and the difference increased after tillage, but decreased after fertilisation. Spring barley dry matter grain yields were reduced by 14% for RT and 27% for DD compared to CT. Measurements of soil mineral nitrogen (N) at sowing showed no difference between the treatments, and could thus not explain the differences in N2O emissions and crop N uptake. It is likely that tillage affected CO2 emissions, N2O emissions and crop growth through different processes, where effects of soil compactness on root penetration and soil aeration and diffusivity on one side and soil organic matter turnover on the other side probably played key roles. (c) 2007 Elsevier B.V. All rights reserved.