Frequently asked questions Frequently asked questions
What information can I find on this website?
You can find information on yield potential, water-limited yield potential, actual yield, yield gaps, and water productivity for major food crops at different spatial scales (location, climate zone, and country). See the Glossary for the definitions of these indicators and the GYGA protocol page for details about the approach used for their calculation.Read the disclaimer >>
Yield gap assessments in the Global Yield Gap Atlas require detailed information about cropping systems, soil properties, long-term weather data, and output from crop simulation models. The Atlas strives to utilize the best available data and most appropriate models following the protocols outlined in the GYGA Methods page. The quality of the best available data vary, however, depending on country and location within country. Therefore, neither the University of Nebraska-Lincoln, Wageningen University, or any of the collaborators on the GYGA project accept any liability for errors or incorrect results in the datasets, the estimates of yield gap or any of the parameters used to estimate yield gaps. Users are referred to the detailed descriptions of methods used and sources of underpinning data as provided as background information underpinning the yield gap assessments for each location included in the Atlas.
What is new here?
Our approach has a strong agronomic foundation. It gives preference to best available sources of weather, soil, and management data, well-validated crop simulation models to estimate potential yield and water productivity, and expert opinion to provide scientifically robust, transparent, and reproducible yield gap assessments. Results are upscaled from location to climate zone and country following a novel bottom-up approach.
How can the information provided in the Atlas be used for?
The Atlas can help determine the untapped crop production potential and identify the most promising regions for investment in agricultural development and technology. The Atlas can also be used to monitor progress towards closing yield gaps and quantitatively estimate impact of R & D investments on yield gap closure over time, and assess the degree to which food self-sufficiency can be achieved through sustainable crop intensification. The Atlas also provides a strong foundation for explaining and mitigating yields gaps and for spatial studies that deal with a wide range of issues such as impact of climate change, land use, environmental footprint of agriculture, and for in-season crop forecasting.
How are yields and water productivity reported in the Atlas?
Yield potential, water-limited yield potential, and actual yield are reported based on the economic yield per harvested area at standard moisture content. Crop water productivity is reported as kilograms of economic yield per unit of crop water availability. See Glossary for a more detailed description.
How are potential and water-limited yields estimated?
These variables are estimated for a given location using crop growth simulation models and local weather, crop management and soil data as input for these models. These location-specific estimates are upscaled following a novel bottom-up approach. See Glossary for definitions of potential and water-limited yield and GYGA protocol page for more details.
How is crop water productivity estimated?
Potential crop water productivity is estimated as the ratio of water-limited yield potential to crop water availability while actual crop water productivity is calculated as the ratio of actual yield to crop water availability. In both cases, crop water availability is estimated from the simulated crop evapotranspiration, which accounts for the stored soil moisture in the rootable soil depth at sowing, rainfall during the growing season, soil moisture left in the rootable soil depth after harvesting and other unavoidable field-level water loses through deep percolation and surface runoff. Crop water productivity is only estimated for rainfed crops. See Glossary for definitions of crop water productivity and GYGA protocol page for more details.
What is a crop growth simulation model?
A crop simulation model is a computer-based program that simulates crop development, growth and yields on a daily basis using daily weather data and soil and management information. In most cases, crop simulation models do not account for the effect of biotic stresses (weeds, pathogens, and insect pests) and nutrient limitations on yield, and estimates of yield potential and water-limited yield assume no yield loss from these constraints.
Why are simulated yields and water productivity always higher than actual yields and water productivity?
The ideal conditions that allow full expression of crop yield potential and most efficient use of water resources rarely occur in producer fields. That is why, even in intensive high-yield cropping systems, actual yields do not reach yield potential. See the Glossary for definitions of potential and water-limited yield potential.
Which countries and crops are covered by the Atlas?
We focus on countries that produce major staple food crops. Please see this link for an overview of the countries and crops currently covered in the Atlas.
What is the approach used in the Atlas to extrapolate results across spatial levels?
The Atlas follows a novel bottom-up scaling approach, in which simulations are performed for a number of sites, strategically selected based on their location within the crop harvested area and major climatic zones of a country, and simulated yields and water productivity are subsequently upscaled from locations to climate zone and country. See the GYGA protocol page for more details.
How can I contribute to the Atlas?
We always welcome new partners. Please contact us by email as indicated below.
How do I cite the Atlas?
The Atlas can be cited as follows: Global Yield Gap and Water Productivity Atlas. Available URL: www.yieldgap.org (accessed on: month, day, year)