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
The search for plant species to reduce nitrous oxide emissions
Could plants be used to reduce nitrification rates in soils and hence reduce nitrate leaching and emissions of nitrous oxide? Results of screening experiments conducted by Dr Saman Bowatte and his team at AgResearch Grasslands campus in Palmerston North suggest that they could. Plus, the variability of nitrification activity detected presents an opportunity to explore alternatives to synthetic inhibitors such as DCD.
The screening experiment measured the potential nitrification rate in soil associated with 126 cultivars of 26 species representing three functional groups used in temperate managed grassland. The team found little difference between the average nitrification values for grasses, legumes and fodder crops, but there was a 71% difference between the lowest and highest nitrification values. Fortuitously, several cases were found where a low nitrification rate was coupled with an above average biomass, suggesting that some currently available cultivars may have lower N emissions - a possibility that is now being tested out in the field.
Over the past New Zealand winter, 18 plant species/cultivars carefully selected from the screening experiment have been quietly growing away in a paddock at Grasslands. The team sowed the experimental plot trial back in mid-April and have been busy weeding, fertilising and watering as required to ensure good growth ready for the next stage of the work. This will involve adding urine to each species/cultivar and then measuring the nitrous oxide emitted.
The hypothesis is that the results seen in the glasshouse experiments will be repeated in the field and that some species will have lower emissions than others. Ideally, the reduction will be of a sufficient magnitude to warrant further investigation and lead on to potential options for low N emitting plant species for use in NZ pastoral settings and beyond.
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