System of Rice Intensification
Rice is the staple food of 3 billion people, providing one-fifth of calories consumed worldwide. Its cultivation is responsible for at least 10 percent of agricultural greenhouse gas emissions and 9 to 19 percent of global methane emissions. That is because flooded rice paddies are ideal anaerobic environments for methane-producing microbes that feed on decomposing organic matter, a process known as methanogenesis.
The System of Rice Intensification (SRI), developed on Madagascar in the 1980s, is a holistic approach for sustainable rice cultivation. It calls for:
- Planting single seedlings with more space between them, rather than by the handful and bunched closely together.
- Watering intermittently and allowing for dry spells, rather than using continuous flooding.
- Tending plots with a rotating hoe, to address weeds and aerate soil, and applying compost.
These methods benefit soil and root systems, while lowering the inputs required for production and increasing crop yields. Now practiced by 4 million to 5 million farmers around the world, SRI yields are 50 to 100 percent higher than conventional rice production. Seed use drops by 80 to 90 percent and water inputs by 25 to 50 percent. Farm incomes can double, as methane emissions drop and soils sequester carbon.
System of Rice Intensification
Project Drawdown defines System of Rice Intensification (SRI) as: an agroecological rice production technique that uses minimal water during the initial stage (just a thin layer), and alternates wetting and drying during the later stage, to increase yield gain and reduce emissions. This practice replaces conventional paddy rice production on smallholdings.
SRI emerged in Madagascar in the 1980s and has become widespread among smallholders, particularly in Asia. SRI’s unique system leads to significant savings in water consumption and enables a more aerobic environment in the rice growth cycle, resulting in reduced methane emissions. Improvement in both organic and inorganic nutrients under SRI result in improved soil conditions, increasing nutrient availability and holding capacity of the soil. Thus, less external fertilizer is required, which in turn reduces the emissions associated with the inefficient use of nitrogen fertilizers.
System of Rice Intensification offers more than 40 percent yield gain, water conservation, lower labor requirements, cost savings, and a better operational environment. The increased yield from the same piece of land could also reduce land clearing for rice cultivation and associated emissions.
SRI has spread rapidly via grassroots, farmer-to-farmer networks. It is currently limited to smallholder rice areas, and adoption should be a high mitigation priority in those areas.
Total Land Area 
Total available land for System of Rice Intensification is 56 million hectares, the total area of smallholder rice production. Current adoption  is 3.5 million hectares (Uphoff, in press).
Adoption Scenarios 
Five custom adoption scenarios were developed based on the current adoption. Some scenarios include early adoption (i.e. 70 percent of allocated land by 2030).
Impacts of increased adoption of System of Rice Intensification from 2020-2050 were generated based on three growth scenarios, which were assessed in comparison to a Reference Scenario where the solution’s market share was fixed at the current levels.
- Plausible Scenario: The most conservative scenario results in SRI adoption on 36.9 million hectares by 2050.
- Drawdown Scenario: Given rice's status as a major contributor of methane emissions from the agriculture sector, the popularity of SRI among farmers, and promotion of SRI by the global scientific community, an aggressive adoption of 53.7 million hectares by 2050 was selected for this scenario.
- Optimum Scenario: Due to the limited area of smallholder rice and the significant potential for methane emission reduction, a 100 percent of allocated land adoption (i.e. 56 million hectares) was chosen for the Optimum Scenario.
Emissions, Sequestration, and Yield Model
Reduced emissions from methane are set at 3.3 tons of carbon dioxide-equivalent per hectare per year, based on 11 data points from 4 sources. Emissions reduction is set at 2.0 tons of carbon dioxide equivalent per hectare per year, based on 2 data points from 2 sources. Reduced emissions from nitrous oxide are calculated at 0.03 tons of carbon dioxide-equivalent per hectare per year, based on 2 data points from 2 sources. Sequestration rates are set at 0.4 tons of carbon per hectare per year, based on 2 data points from 2 sources.
Yield gains compared to business-as-usual annual cropping were set at 44.8 percent, based on meta-analysis of 39 data points from 8 sources.
First costs are US$0 per hectare, as SRI uses existing equipment and infrastructure.  For all agricultural solutions it is assumed that there is no conventional first cost, as agriculture is already in place on the land. Net profit per hectare is calculated at US$1,103.63 per year for the solution (based on meta-analysis of 15 data points from 5 sources), compared to US$30.47 per year for the conventional practice (based on 6 data points from 6 sources).
Drawdown’s Agro-Ecological Zone model allocates current and projected adoption of solutions to the planet’s forest, grassland, rainfed cropland, and irrigated cropland areas. Adoption of System of Rice Intensification was the highest priority for cropland due to yield increases.
Total adoption in the Plausible Scenario is 36.9 million hectares in 2050, representing 65.8 percent of the total suitable land. Of this, 33.4 million hectares are adopted from 2020-2050. The emissions impact of this scenario is 3.1 gigatons of carbon dioxide-equivalent reduced by 2050. Net cost is US$0. Net savings is US$677.8 billion. Yield gains result in an additional yield of 347.3 million metric tons of rice between 2015-2050.
Total adoption in the Drawdown Scenario is 53.7 million hectares in 2050, representing 95.8 percent of the total suitable land. Of this, 50.2 million hectares are adopted from 2020-2050. The impact of this scenario is 5.0 gigatons of carbon dioxide-equivalent by 2050.
Total adoption in the Optimum Scenario is 55.6 million hectares in 2050, representing 99.2 percent of the total suitable land. Of this, 52.1 million hectares are adopted from 2020-2050. The impact of this scenario is 5.9 gigatons of carbon dioxide-equivalent by 2050.
The Intergovernmental Panel on Climate Change (Smith, 2007) estimates emissions reductions of 0.2 gigatons of carbon dioxide-equivalent per year by 2030 through rice management. Drawdown's two rice solutions combined provide 0.16-0.26, a close match to the benchmark.
This study could be improved by obtaining additional data points on emissions reduction and carbon sequestration in SRI systems.
Rice is a staple crop of critical importance, particularly in Asia. Rice production is currently a major contributor of methane. Fortunately, low-methane rice production systems including the System of Rice Intensification are ready to be scaled up. Wide adoption of these practices can have a significant impact on climate change mitigation. SRI yield gains more than compensate for the minor yield losses under Drawdown's improved rice cultivation solution. Wherever smallholders produce rice, this solution should be closely considered for broad-scale adoption.
 To learn more about the Total Land Area for the Food Sector, click the Sector Summary: Food link below.
 Current adoption is defined as the amount of functional demand supplied by the solution in the base year of study. This study uses 2014 as the base year due to the availability of global adoption data for all Project Drawdown solutions evaluated.
 To learn more about Project Drawdown’s three growth scenarios, click the Scenarios link below. For information on Land Use Sector-specific scenarios, click the Sector Summary: Food link.
 All monetary values are presented in US2014$.
 For more on Project Drawdown’s Food Sector integration model, click the Sector Summary: Food link below.
Full models and technical reports coming in late 2017.