Plants & GHGs

The NZAGRC’s former nitrous oxide and soil carbon work streams were combined into one programme this year. This ensures a strong overall framework, closer communication and full GHG analyses across the programme. The programme focusses on three key areas:

1. Identifying and prioritising plant traits for low GHG emissions;

2. Mitigation practices to maintain soil carbon and reduce nitrous oxide emissions at paddock scale; and

3. Defining the achievable soil carbon stabilisation capacity of New Zealand grassland soils.

Current progress and research stories

Changes in denitrification rate and N2O/N2 ratio with varying soil moisture conditions in New Zealand pasture soils

Jha, N., Saggar, S., Tillman, R., & Giltrap, D. (2012). Changes in denitrification rate and N2O/N2 ratio with varying soil moisture conditions in New Zealand pasture soils In: Advanced Nutrient Management: Gains from the Past - Goals for the Future. (Eds L.D. Currie and C L. Christensen). 

Abstract

Denitrification is the primary process of N2O production in temperate grassland soils and accounts for 60% of the total N2O emissions globally. There are various soil and environmental factors that regulate denitrification and affect denitrification rate (DR) and N2O/ N2 ratio. Among these, soil moisture is the most important. Generally, DR increases and N2O/N2 ratio decreases with increasing soil water content. However, the effect of changing soil moisture on DR and N2O/N2 ratio may vary with the type of soil, its nutrient status and the management practices followed on the farm. The interrelationships among the various factors affecting DR are not very well quantified.

Therefore, the current study was planned to investigate the effect of soil moisture on DR and N2O/N2 ratio in five different New Zealand pasture soils with varying physical and chemical characteristics such as soil texture, total porosity, pH, NO3- and NH4+ content, total nitrogen (TN), total carbon (TC), microbial biomass carbon (MBC) and denitrification enzyme activity (DEA). The experiment involved incubation of surface (0-10cm) and subsurface (10-20cm) soil samples at field capacity (FC) and complete saturation at constant temperature (25oC). DR and N2O/N2 ratio were estimated using an acetylene inhibition (AI) technique.

Denitrification rates were higher in soils incubated at saturation than in soils incubated at FC. Similarly, the N2O/N2 ratio decreased in soils when incubated at saturation as compared to FC. The extent of these increases in DR and decreases in N2O/N2 ratio with increasing moisture content varied among the soils due to differences in NO3- and NH4+ content, MBC and DEA of the soils.

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