Rice Yield Gaps
According to a yield gap assessment of rice granaries in Asia, the exploitable or attainable yield gap is substantial, ranging from 1 to 3.6 tons/ha.
Actual rice yields and potential yield gaps in CORIGAP partner countries.
In Southeast Asia alone, closing this rice yield gap would increase total annual production of milled rice by an estimated 55 million tons, providing additional food for some 500 million people.
The Closing Rice Yield Gaps in Asia with Reduced Environmental Footprint (CORIGAP) Project aims to improve food security and alleviate poverty by reducing rice yield gaps in six major irrigated rice granaries in Asia.
What is a yield gap?
The difference between the potential yield and actual yield obtained by farmers
What is actual yield?
The average yield achieved by farmers in a given region under dominant management practices (sowing date, cultivar maturity, and plant density) and soil properties, ideally over at least a 3-year period
What is potential yield?
The yield of the crop grown with unrestricted water and nutrients, and without stress from other living organisms
An example to demonstrate yield gaps (in green) in CORIGAP sites as calculated by the difference between the average actual farmers' yield and the best farmers' yield (top 10%).
Farmer yield estimates came from farmer surveys of the wet season of 2013 (China, Thailand, Myanmar, Vietnam), dry season of 2013 (Sri Lanka), and wet season of 2009 (Indonesia).
Exploitable/attainable yield gap
An exploitable/attainable yield gap is the difference between actual yield and 80% of modeled potential yield (although, this level depends on price ratios).
• Best farmers’ yields have been shown to be near this exploitable yield level.
Potential yields estimated by crop growth simulation models are not considered to be economically viable because:
• The response of yields to more production inputs decrease as maximum yields are approached.
- Yields above 80% have lower nutrient-use efficiencies.
- Yields at 70–80% are associated with the highest profits.
• It is impossible for a large population of farmers to achieve perfection in crop and soil management.
Different production levels as determined by growth-defining, -limiting, and -reducing factors. Modified from Van Ittersum et al (2013).
Identifying local yield gaps
Currently, there are inconsistent values reported on rice yield gap data in Asia, with some values being extremely different to others. Some value are outdated, and some are extrapolated across regions/cropping systems.
Also, because of the limitations in these methods of calculation, a rigorous review of the available data, along with validation through researcher-led participatory field trials, is required to properly identify the exploitable yield gap that can be targeted in specific rice granaries in partner countries.
It is thus important that up-to-date data is collected over several seasons, with the following factors to be considered:
• cropping system, e.g. rainfed/ irrigated,
• variety (modern/traditional; high/low yielding);
• season and planting date;
• soil type
CORIGAP’s focus is on rice granaries, and there is a need to collect data over several seasons for these regions. Data will be collected through national statistics, household surveys, farmer diaries, and researcher-led field trials. Aside from the factors mentioned previously, data on whether a specific technology was adopted is also needed. Such data collection has already begun in China, Myanmar, and Vietnam.
Measuring potential yield
Potential yield can be measured using
1. Crop growth simulation models (e.g., ORYZA2000)
Using these models requires site-specific data and rigorous validation, and is still to be refined for Southeast Asia.
2. Experiment yields
Using experiment yields to measure potential yield requires well-managed field studies in which yield-limiting and yield-reducing factors are eliminated.
3. Best farmers’ yields—upper 10 percentile per season + year
The challenge in using best farmers’ yields to measure potential yield is that it is difficult to know if all abiotic and biotic stresses were avoided.