- Yield gaps result from shortfalls in the crop growth environment that are not resolved by current agricultural management practices.
The need to double global food production by 2050 is widely accepted by most food policy analysts, as is the concept of doing it mostly through ‘sustainable intensification’ on current cropland. A recent analysis from the University of Minnesota and McGill University in Montreal, Closing Yield Gaps Through Nutrient and Water Management published in Nature, applies current agricultural technology and management techniques to ‘underperforming landscapes’ to increase yields, while also decreasing the environmental impacts of agricultural systems.
The analysis has an environmental bent because the lead author, Nathaniel D. Mueller, is with the Institute on the Environment at the University of Minnesota. He has a fellowship from the College of Food, Agricultural and Natural Resources Sciences. His co-authors at the University of Minnesota are also from the Institute on the Environment. The McGill University co-author is in the Department of Geography and Global Environmental and Climate Change Center.
The researchers analyzed 17 major crops that make up 76 percent of harvested global cropland. They found that increasing yields to 100 percent of attainable yields would increase production by 45-70 percent for most crops analyzed, with corn production increasing by 64 percent, wheat 71 percent and rice 47 percent. Attainable yields were “determined by identifying high-yielding areas within zones of similar climate.” Environmental impacts could be reduced by eliminating nutrient overuse and still increase by 30 percent the production of corn, wheat and rice. Eastern Europe and Sub-Saharan Africa have great opportunities even if yields were only increased to 50 percent of attainable yields. East and South Asia also have intensification opportunities based on the amount of land and variability of yields.
Yield gaps result from shortfalls in the crop growth environment that are not resolved by current agricultural management practices. The authors focused specifically on irrigation and fertilizer and found that these two factors plus climate account for 60-80 percent of the global-yield variability for most crops. Crop-specific irrigation data were used, as were crop specific-fertilizer application rates for nitrogen, phosphate and potash. Irrigation areas are heavily concentrated in East Asia, South Asia and parts of the U.S., and high fertilizer application rates were found in developed countries and a few rapidly developing ones. Eastern Europe was shown to be nutrient deficit for wheat, and Eastern Europe and West Africa were nutrient deficient for corn.
A combination of water and nutrient limitations were found in East Africa and Western India for corn, the U.S. Great Plains and Mediterranean Basin for wheat, and Southeast Asia for rice. For example, in Sub-Saharan Africa closing 50 percent of the corn yield gap can be achieved by adding fertilizer, but closing 75 percent of the yield gap requires fertilizer application and irrigation over most of the region. The model used in the analysis managed the combination of fertilizer and irrigation.
The researchers suggested that fertilizer nutrient use can be reduced in regions where the data indicate there is overuse. Their estimates indicate that applications on corn, wheat and rice could be decreased by 28 percent for nitrogen, 11 million metric tons (MMT), and 38 percent for phosphate, 5 MMT. China was noted as a country with particularly dramatic overuse of nutrients. Achieving 75 percent of attainable yields while eliminating overuse of fertilizer is estimated to result in a net 9 percent increase in nitrogen use, a net 34 percent increase in use of potash and a net 2 percent reduction in use of phosphate.
The researchers recognized that other agronomic practices can lessen the environmental impact of changes in irrigation and fertilizer use. They include precision agriculture techniques, conservation tillage, high-yielding hybrids, increased plant populations and multifunctional landscape management. These are basic tools for higher crop yields used in North American, South America, Western Europe and Australia. They mentioned the benefits of organic fertilizers, but noted they are omitted from the analysis due to data limitations. Later in the analysis they emphasize again the importance of management practices “including crop rotation patterns, organic nutrient inputs, micronutrients, improved seed quality, conservation tillage and pest management.” More inputs are of no value if the planting seeds do not have the genetic capability of achieving higher yields or the plants succumb to insect pressures.
One limitation this approach to analysis is it does not account for new technology that may become part of standard agronomic practices in a few years. The yield data are centered on the 2000 crop year; much has changed in production practices over the last 12 years. New practices may result in better yields than now expected.
The researchers also recognized how issues of fresh water availability conflict with the greater use of irrigation. That has become a major issue near rapidly growing urban populations and industrial areas.
Farmers use land, water, air and technology to produce food. Over recent decades the developed countries of the world have become proficient enough at food production and output of other products that can be traded for food that consideration can now be given to devoting potential farmland to other uses. That has caused a shift in interest groups when food production issues are addressed.
Researchers with an interest in the trade-offs for land used for food versus land for environmental uses now have a seat at the food policy table. Their most logical allies are farmers and ranchers with modern technology that will increase output per unit of inputs to meet the food needs of the world population in 2050 without requiring the use of all the land that could potentially grow food
The analysis supports the presumption that much of the additional food needed to have a well-fed global population in 2050 can be met from existing cropland. The challenge still remains on how to transfer the technology from the areas where it is currently used to those areas with ‘underperforming landscapes’.