Submitted to: Science
Publication Type: Review article
Publication Acceptance Date: 4/9/2014
Publication Date: 5/2/2014
Citation: Ort, D.R., Long, S.P. 2014. Limits on yield in the corn belt. Science. 344:484-485. Interpretive Summary:
Technical Abstract: In terms of total global production corn (Zea mays L.) is the most important food and feed seed crop. 967 million metric tons (38,000 million bushels) was produced in 2013, 36.5% of that within the USA, and most of that in the Midwest. The USA is by far the largest exporter of primary feed- and food-stuffs in the world of which corn accounted for 50%. What happens with US corn crop therefore has a major influence of global prices and supply of primary food and feed stuffs. As noted by Lobell et al. yields have increased until recently, a key element being breeding and management that has allowed farmers to increase the number of plants per acre without loss of yield per plant. Simultaneously there has been effort to increase drought tolerance. Lobell et al. use a uniquely detailed dataset for farms across the major corn producing region, or Corn Belt, which contains yields, environmental and management variables in each year from 1995-2012. They show that while yield has increased, drought sensitivity (the ratio of drought to water sufficient yields) has increased, and not decreased. A key implication for global supply is that production in the Corn Belt will become more and not less sensitive to drought in this key growing region. This may be explained by the fact that with increased plants per acre, the amount of soil water available to each plant will be less. The most novel and far reaching finding of this study is that yield was most sensitive to water vapor pressure deficit (VPD) a factor that has rarely been included in past analyses, but has major implications for yields as climate change progresses in the Corn Belt. What impact will this increase have? Average precipitation across the study area is 33 inches and if we assume that 70% of this is available to the crop then at today’s average growing season a VPD of 2.2 kPa would support a yield of 214 bu/acre. This is more than sufficient to support the average yield of ~170 bu/acre for this region in 2013, but limiting on farms receiving less than 25 inches or on readily draining soils. However, if VPD rises to 2.65 kPa as predicted for 2050 the average rainfall of 33 inches would now only support 177 bu/acre thereby making production far more vulnerable even to moderate droughts. However, if improved genetics and agronomy can achieve the 70% yield increase to 272 bu/acre projected to be needed by 2050 this would require 50 inches of precipitation per year.