Rice Management Strategies

In this post I am going to go back to rice paddies and discuss possible mitigation strategies aiming to reduce future methane emissions from these fields.  This is briefly outlined in the IPPC Report.  

In a paper by Lindau (1994), fertilisers containing nitrogen were added to rice fields before they were flooded in Louisiana, USA.  Then, during the growing season methane fluxes were measured at regular intervals.  As a result, it was found that methane emissions reduced, where ammonium sulphate was added emissions reduced by 55% and where potassium nitrate was added they reduced by 59%.  However these results are very variable as discussed in an article by Banger et al (2012) who state that adding nitrogen fertilisers to rice paddies have complex impacts on methane emissions.  They found that out of 155 data pairs in rice soils, 98 of these had increased methane emissions.  The downside to this strategy is that it does have variable results and it can also lead to increases in nitrous oxide emissions.  

Cai et al (2000) undertook a study at 8 sites in China finding that methane emissions varied greatly between sites.  They found that in the non rice season, waterlogged and flooded fields continued to emit methane, but they did find that these emissions were lower at sites at mid and higher slope locations compared to those at the base of slopes.  This is thought to be as a result of better drainage.  A paper by Gou and Zhou (2007) links to this, they describe various rice management strategies, one being field drainage in the off-rice season.  By draining the fields the anaerobic environment is lost which reduces methane emissions.  They also suggest that intermittent irrigation of rice paddy fields can be effective in reducing emissions.  However, a downside is that draining and flooding the fields is a very water intensive process.  

In the paper by Gou and Zhou (2007) they also suggest that rice variety affects methane emissions and often hybrid varieties lead to lower methane emissions than common ones. They suggest this as a possible mitigation strategy to lower methane emissions.  They also discuss fertiliser management, where chemical fertilisers are replaced with organic.  it has been suggested that replacing chemical fertilisers with peat moss can reduce methane emissions.  

These strategies offer potential to reduce methane emissions from rice fields.  The demand for rice is growing with the population.  Draining is probably the most successful rice management strategy as it does not alter the crop yield and will consequently be the most appealing to farmers.  However the downside of this is that it does require vast amounts of water which may not be available in some regions and could also be very expensive.  Adding nitrogen fertilisers has been shown to be successful in some areas but it is variable on location and fertiliser type.  There is also the negative aspect that it can increase nitrous oxide emissions.  Similarly changing the rice variety maybe difficult to implement as some hybrid species may have difficulty germinating in some locations and they may not provide the same yields as common rice, which could be an economic cost to farmers.