Fertilisation with muriate of potash (MOP) can significantly reduce emissions of methane from flooded soils planted with rice. Rice cultivation is responsible for 10% of GHG emissions from agriculture. In developing countries, the share of rice in GHG emissions from agriculture is even higher, e.g., it was 16% in 1994.
See 'Rice production technologies' for an overview of all climate change mitigation technologies related to rice cultivation.
Potassium applications to rice field soils prevent a drop in redox potential and reduce the contents of active reducing substances and Fe2+ contents. Potassium amendments also inhibit methanogenic bacteria and stimulate methanotrophic bacterial populations. In addition to producing higher rice biomass (both above and below ground) and grain yield, potassium amendments can effectively reduce CH4 emission from flooded soil, and this could be developed into an effective mitigation option especially in potassium deficient soils (Babu et al., 2006), see figure 1.
It is standard practice to fertilise with additional potassium fertiliser on potassium-deficient paddy soils, at least in more developed countries. In less developed countries, it is not as prevalent due to less awareness about usage, cost and availability of fertiliser inputs.
- Chemical fertilisers mitigate methane emissions more quickly compared to the slow processes of organic amendments.
- Chemical fertilisers also fulfill the nutrient requirements of crops, thus helping in sustaining productivity while mitigating methane emissions.
- Chemical fertilisers sometimes improve soil health if used with care to maintain nutrient balance in soil.
- The potassium fertiliser must be precisely applied in order to avoid negative effects on field fertility.
- Chemical fertilisers that are applied in excess to the normal ratio generally change the nutrient composition of the soil besides affecting their physical structure. This affects adversely both methane oxidation and methanogenesis.
In potassium deficient soils, applications of potassium fertiliser generally increase yields significantly; the value of the increase in yield exceeds the costs of the fertiliser treatments. Therefore, under these conditions, the reduction in methane emissions is an added benefit whose mitigation cost is effectively zero. In addition, K fertilisation can reduce methane emissions by half (figure 1).
Fertiliser costs can be an issue, as well as the need to provide education about their appropriate and precise use.
Babu, J.Y., Nayak, D.R., and Adhya, T.K. (2006): Potassium Application Reduces Methane Emission from a Flooded Field Planted to Rice. Biol. Fertil. Soils. (2006), 42:532-54.