Closing Yield Gaps Through Nutrient and Water Management

In the coming decades our agricultural system is going to be increasingly compromised as it struggles to keep up with a growing world population and diminishing natural resources.  Couple that with the agricultural system’s adverse effects on the environment, and we are presented with a mammoth of a problem.  Mueller et al. (2012) performed a global-scale assessment of methods to increase yields on underperforming landscapes while simultaneously decreasing their environmental impacts so that yield gaps can be minimized in underperforming farms.  By analyzing the yield of crops in farms of varying climate and management practices and then comparing them with each other, the authors were able to formulate means of closing yield gaps.  While the researchers found that there were large opportunities to increase crop production and lower the environmental impact, there were some limitations to their findings as they were mainly applicable to the regional or global scale, and did not take into account all factors of agriculture.—Anthony Li
Mueller N. D., Gerber J. S., Johnston M., Ray D. K., Ramankutty N., Foley J. A. 2012.  Closing yield gaps through nutrient and water management. Nature 490, 254–257

The authors examined 17 major crops that could be grown all over the world, including maize, rice, wheat, barely, sorghum, etc.  They investigated each crop’s yield gap, which was determined by comparing observed yields to ‘attainable yields,’ estimated by identifying high-yielding areas of the same crop within zones of comparable climate.  These yield gaps were calculated based on the percent of how much out of the maximum possible crop yield can the area under study attain, as determined in comparable areas with high yields. 50% meant that the examined area had increased yields up to half of what is attainable and 100% meant the examined area had increased yields up to what is completely attainable. With the yield gaps determined, the authors examined the potential changes in irrigated area and nutrient application needed to close them to within 75% of attainable yields.  By obtaining fertilizer and irrigation data to parameterize nutrient response curves and rain-fed maximum yields, the authors used nonlinear regression analysis for each climate zone to estimate changes in inputs necessary to close yield gaps.
They found that it was possible to attain a 30% increase in production of major cereals while reducing the environmental impact of agriculture by eliminating nutrient overuse.  They also found that 73% of underachieving areas could close yield gaps by focusing on nutrient inputs, 16% of the underachieving areas could close yield gaps by increasing irrigation, and that by increasing both irrigation and nutrient application, the yield gaps could be closed in all underachieving areas.  The authors postulated that if we could close all yield gaps to 100% of attainable yields, worldwide crop production could increase by 45% to 75%.  This study not only shows us what we can attain in crop yields, but also showed us some characteristics of the crops themselves.  Yields of some crops such as sorghum, millet, and groundnut were more influenced by climate, while other crops such as barley, sugar beet, and oil palm were more influenced by farmland management. 
The findings of this paper spell an optimistic future for our agricultural systems.  If we can decrease overuse of crop inputs wherever possible on top of increasing irrigation and nutrient application where needed, we can expect a great increase in crop yield and improvements to the environment.  If we addressed the imbalances and inefficiencies shown in this study, global consumption of nitrogen fertilizer could decrease by 11 million tons and phosphate fertilizer could decrease by 5 million tons on maize, wheat, and rice crops without impacting current yields.  It is also possible to close global yield gaps on major cereals to 75% of attainable yields with minimal changes on fertilizer usage.  Closing yield gaps is more beneficial long term than short; the authors note that “marginal returns for additional inputs, regional land-management policies, limits on sustainable water resources and socio-economic constraints” make short-term goals less appreciable.
As of now, the global agricultural system causes immeasurable harm to the environment, and this harm will only be exacerbated as the demand for more food rises.  This paper dispels some doom and gloom by showing how efficient and less polluting our farms can become with simple changes.  Although the findings of this paper cannot be applied to all current systems, since they did not take into account all factors that influence agricultural production, they it pave the path for future research into sustainable and efficient agriculture.

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