"We find that there are pretty dramatic increases in crop production – on the order of 45 to 70% for most major crops – possible from closing the so-called 'yield gaps' between the least and most productive areas with the same growing characteristics," Nathan Mueller of the University of Minnesota, US, told environmentalresearchweb. "We also analyse what we expect the changes in fertilizer and irrigation management might need to be to close these yield gaps. This is our first consistent, global picture of management changes on global croplands necessary to close yield gaps."

Mueller and colleagues from the University of Minnesota and McGill University, Canada, found that global yields are strongly controlled by fertilizer use, irrigation and climate. These factors could account for 60–80% of yield variability for most major crops. Under the right conditions, maize production could see an increase of 64%, wheat a 71% rise and rice a boost of 47%.

Even if yields were increased to only 50% of those attainable, areas such as Eastern Europe and Sub-Saharan Africa could show large production gains. The team says East and South Asia also have "substantial intensification opportunities" because of their vast agricultural lands and the variability in their yields.

"We need to dramatically increase global food production to meet growing demands from population growth and diet," Nathan Mueller of the University of Minnesota, US, told environmentalresearchweb. "At the same time, we need to improve the environmental performance of agriculture, particularly in terms of water use and water quality, often tied to fertilizers. We wanted to understand how these two great challenges could be tackled together."

During the study, the researchers developed a global crop-specific data set of nitrogen, phosphate and potash fertilizer-application rates. The nations using high fertilizer-application rates tended to be high income and some rapidly developing countries, they discovered. Irrigation, meanwhile, was strongly concentrated in South Asia, East Asia and parts of the US.

In nearly three-quarters of underachieving areas, closing yield gaps in maize, wheat and rice production to within 75% of their attainable yields (which would increase global production by 29%) would need a focus on nutrients only. Eastern Europe and West Africa are hotspots of nutrient limitation for maize, the study showed, while Eastern European wheat is also nutrient limited. Increasing irrigation alone would help in only 16% of underachieving landscapes.

Jointly increasing the irrigated area and nutrient application could close yield gaps in all locations, according to the team. Both nutrients and water acted as limits across East Africa and Western India for maize, in portions of the US Great Plains and Mediterranean Basin for wheat, and in Southeast Asia for rice.

"Closing yield gaps has previously been identified as one of the five main strategies to meet future food demand and reduce the environmental impact of agriculture," said Mueller. "Here we provide much more detail about the possibilities across the globe for closing yield gaps, as well as how yield gaps could potentially be closed through changes in management."

Mueller and colleagues also highlighted areas that could cut back on overuse of nitrogen and phosphorus fertilizers, providing benefits for water quality, public health and climate change. "Combining efforts to cut back overuse with efforts to use nutrients more wisely where they will do the most good can boost production of some of our major crops by 30% with fairly minimal changes to total global nitrogen and phosphorus use," he said.

Writing in Nature , the researchers said that closing yield gaps may not always be desirable or practical in the short term, given marginal returns for additional inputs, regional land-management policies, limits on sustainable water resources and socio-economic constraints. They added that using precision agriculture techniques, conservation tillage, high-yielding hybrids, increased plant populations and multifunctional landscape management can help mitigate the environmental impact of intensive agriculture. But changes in water availability resulting from climate change may conflict with projected irrigation requirements.

Now the researchers are looking to "really dig into our irrigation projections to understand where irrigation increases are possible in light of sustainable water supplies, and where we must limit irrigation expansion".