Are we approaching a water ceiling to maize yields in the United States?

Abstract

While annual precipitation in much of the US Corn Belt is likely to remain constant, atmospheric vapor pressure deficit (VPD), the driver of crop water loss (evapotranspiration; ET), is projected to increase from~2.2 kPa today to~2.7 kPa by mid-century primarily due to the temperature increase. Without irrigation, it has been hypothesized that the increase in VPD will create a ceiling to future increases in maize yields. We calculated current and future growing season ET based on biomass, water use efficiency, and the amount of yield these levels of ET would support for maize production in the Midwest USA. We assumed that the production of more grain will necessitate a proportional increase in the production of biomass, with a corresponding increase in ET. Here we show that as VPD increases, maintaining current maize yields (2013-2016) will require a large expansion of irrigation, greater than threefold, in areas currently supported by rain. The average predicted yield for the region of 244 AE 4 bushels/acre (15,316 AE 251 kg/ha) projected for 2050, assuming yield increases observed for the past 60 yr continue, would not be possible with projected increases in VPD, creating a water ceiling to maize yields. Substantial increases in maize yields and the production of high yielding grasses for bioenergy will require developing cultivars with greater water use efficiency, a trait that has not been a priority for breeders in the past.

Machine learning enabled phenotyping for GWAS and TWAS of WUE traits in 869 field-grown sorghum accessions

“…Taken together these results demonstrate that enhanced iWUE is achieved either through low g s or through coupling high A N with moderate g s . While in the past it was suggested that WUE across C 4 species was almost invariant (DeLucia et al, 2019), this study builds on work in sugarcane (Inman-Bamber et al, 2016) to suggest that meaningful variation does exist. Our generalized estimates of heritability for A N and g s (Figure 5) were similar to those estimated in a recent survey of the same traits in a smaller panel of grain sorghum accessions (Ortiz et al, 2017) and sufficiently high to justify targeting them as traits for selection.…”

“…The trade-off between carbon gain and water use is a fundamental constraint for crop productivity and environmental resilience (Bailey-Serres et al, 2019; DeLucia et al, 2019; Leakey et al, 2019). More specifically, improving WUE is recognized as a means to enhance the utility of sorghum as a biofuel feedstock (Mathur et al, 2017; Meki et al, 2017).…”

“…C 4 crops including maize, sorghum, sugarcane, millet and Miscanthus are heavily studied as sources of food, feed, fuel and fiber. However, less research has been directed towards understanding and improving WUE and its component traits in C 4 crops, possibly because they already achieve high WUE as a result of the CO 2 concentrating mechanism they possess (DeLucia et al, 2019). Nevertheless, mechanistic modeling suggests that enhancing intrinsic WUE ( iWUE ) by reducing stomatal conductance ( g s ) while maintaining rates of net CO 2 assimilation ( A N ) can increase biomass production in C 4 as well as C 3 species across a broad range of environmental conditions (Truong et al, 2017; Leakey et al, 2019).…”

Quantifying irrigation cooling benefits to maize yield in the US Midwest

“…The spatiotemporal variations in the irrigation effect found in our results highlight the strong influence of background climate conditions. With projected shifting precipitation patterns and more frequent droughts and heatwaves in the future (Huang et al, ; Wuebbles et al, ), a large expansion of irrigation would be required to sustain current maize yield trends in the United States (DeLucia et al, ; McDonald & Girvetz, ). Within this context, irrigation effects are expected to be intensified, leading to a greater synergistic effect of crop yield increase and cooling benefit.…”

Contrasting long-term temperature trends reveal minor changes in projected potential evapotranspiration in the US Midwest

“…Some studies have suggested that corn in the Midwest will require ~35% more water inputs to reach yield targets by 2050 20 , 21 , arguing that sustaining yield gains will not be feasible without widespread expansion of irrigation infrastructure 22 . This claim is questionable, in part due to evidence showing that large differences in crop biomass and yield can be achieved with the same amount of ET, both within and across species with similar growing-season length 14 , 23 .…”