Nitrous Oxide Emission From Alfalfa Stands And Relation Management Factors

Advancing knowledge concerning greenhouse gases has resulted in more diversified research. Where earlier investigations have focused typically on carbon dioxide and methane, current research tends to focus on Nitrous-oxide. The major research domains of Nitrous-oxide emissions are on farmland and rice paddies although Nitrous-oxide emissions from Chinese cultivated grasslands are still limited. With the implementation of the "returning cultivated land to forestry" project in Western China, the Nitrous-oxide emission potential of Alfalfa, a high grade leguminous forage grown extensively in this region, cannot be ignored.This investigation examined the potential of Alfalfa from the hilly loess ravine area and the loess plateau Han Yuan area to influence greenhouse gas emissions through the examination of nitrous-oxide emission characteristics such as nitrogen treatment, planting years and sowing ways. A comparative analysis with Kentucky bluegrass and sainfoin was undertaken and static boxes-gas chromatography was used to determine nitrous-oxide emissions flux of soil/vegetation system in each cutting period. An in-depth analysis of the change in index combined with grass soil total nitrogen, NO3" and NH4+, organic matter, soil pH, soil temperature and humidity was also conducted. This experiment initially proved the cultivation of Alfalfa will influence greenhouse gas emissions on the following aspects:1. With the increase of nitrogen, Alfalfa grassland nitrous-oxide emissions average flux increased gradually. It was found that the Emissions flux from small to large was:no nitrogen treatment (N-0) is0.02mg/(m2·h);nitrogen application rate50kg/ha (N-50) is0.37mg/(m2·h); nitrogen application rate100kg/ha (N-100) is0.50mg/(m2·h).The nitrous oxide emissions flux range under no nitrogen treatment was-0.33-0.45mg/(m2·h).The nitrous-oxide emissions flux range under N-50treatment was0.18-0.57mg/(m2·h).The nitrous-oxide emissions flux range under N-100treatment was0.21-0.94mg/(m2·h); nitrous-oxide emissions flux of Alfalfa in nitrogen treatment had a significant positive correlation with0-10cm soil total nitrogen and very significant positive correlation with ammonium nitrogen content.2. The nitrous-oxide emissions average flux of7years Alfalfa grassland was greater than2years Alfalfa grassland nitrous-oxide emissions average flux, it respectively for0.22mg/(m2·h) and0.06mg/(m2·h). The nitrous-oxide emissions flux range of7years Alfalfa was-0.09-1.02mg/(m2·h); the nitrous-oxide emissions flux range of2years Alfalfa was-0.08-0.31mg/(m2·h). Nitrous-oxide emissions flux of Alfalfa of different ages had significant negative correlation with0-10cm soil pH.3. Nitrous-oxide emissions flux of broadcast-sown alfalfa grassland was higher than that of strip-sown alfalfa, it respectively for0.05mg/(m2·h) and-0.05mg/(m2·h). The nitrous-oxide emissions flux range of broadcast-sown alfalfa grassland was-0.08-0.31mg/(m2·h); the nitrous-oxide emissions flux range of strip-sown alfalfa grassland was0.16-0.08mg/(m2·h). Alfalfa grassland nitrous-oxide emissions flux of different sowing ways had a significant positive correlation with0-10cm of soil organic matter content.4. Nitrous-oxide emissions flux of alfalfa was smallest, followed by sainfoin and then Kentucky bluegrass, with0.02,0.05,0.15mg/(m2·h) respectively. The nitrous-oxide emissions flux range of Kentucky bluegrass was-0.32-0.51mg/(m2·h); The nitrous-oxide emissions flux range of sainfoin was-0.50-0.45mg/(m2·h); the nitrous-oxide emissions flux range of alfalfa was-0.33-0.45mg/(m2·h). The nitrous-oxide emissions flux of these grasses had significant positive correlation with0-10cm of soil organic matter content.