The contribution of solar brightening to the US maize yield trend

Abstract

Predictions of crop yield under future climate change are predicated on historical yield trends 1-3 , hence it is important to identify the contributors to historical yield gains and their potential for continued increase. The large gains in maize yield in the US Corn Belt have been attributed to agricultural technologies 4 , ignoring the potential contribution of solar brightening (decadal-scale increases in incident solar radiation) reported for much of the globe since the mid-1980s. In this study, using a novel biophysical/empirical approach, we show that solar brightening contributed approximately 27% of the US Corn Belt yield trend from 1984 to 2013. Accumulated solar brightening during the post-flowering phase of development of maize increased during the past 3 decades, causing the yield increase that previously had been attributed to agricultural technology. Several factors are believed to cause solar brightening, but their relative importance and future outlook are unknown 5-9 , making prediction of continued solar brightening and its future contribution to yield gain uncertain. Consequently, results of this study call into question the implicit use of historical yield trends in predicting yields under future climate change scenarios.

The important but weakening maize yield benefit of grain filling prolongation in the US Midwest

“…A previous study suggested the solar brightening during GFP is responsible for about 27% of the observed increase in US maize yield from 1984 to 2013 (Tollenaar et al., ). However, we did not find a significant increase in solar radiation across the four corn states considered during the study period when using the same solar radiation dataset integrated over the grain filling period (Supporting Information Figure S6).…”

“…The weekly reported area ratios were interpolated using sigmoid function. The target phenological stages (emerged, silking, dent, and mature stages) were then determined as the date when the interpolated area ratio reached 50% on a state level (Tollenaar et al., ). The phenological dates from CPR were used as a reference to evaluate the MODIS‐based estimations.…”

“…As the world's largest producer of maize, the United States has seen a steady increase in maize yield since the 1950s through improvements in agronomic practices, genetic technology and favorable growing conditions despite interannual yield variability related to hot and dry summers (USDA, ). Several possible mechanisms have been investigated in order to understand this increasing trend in yields, including: expansion of more heat‐tolerant cultivars (Driedonks, Rieu, & Vriezen, ), delayed foliar senescence or stay‐green traits (Thomas & Ougham, ), new cultivars adapted to higher sowing density (Duvick, ; Tollenaar & Wu, ), development of pest resistant maize cultivars through genetically engineering (NRC, ), enhanced water use efficiency under rising atmospheric CO 2 (Jin, Ainsworth, Leakey, & Lobell, ; Lobell & Field, ), and increase in accumulated solar radiation during the postflowering phase (Tollenaar, Fridgen, Tyagi, Stackhouse, & Kumudini, ). A drought sensitivity analysis over the US Midwest based on field maize yield data showed, however, higher sowing density brought about side effect that field maize yield sensitivity to water stress became increased (Lobell et al., ).…”

The fertilization effect of global dimming on crop yields is not attributed to an improved light interception

“…Various approaches have been used to quantify the impact of global dimming. A popular approach is to quantify agroecosystem productivity, crop yields, in response to incident global radiation and diffuse radiation fraction changes by using historical climate and crop yield data (Lobell & Asner, 2003;Proctor et al, 2018;Tollenaar et al, 2017;Yang et al, 2013;Zhang, Li, Yue, & Yang, 2017), but these results were usually beset by the collinearity among climate variables (especially among solar radiation, temperature, precipitation ;Lobell & Burke, 2009;Lobell, Schlenker, & Costa-Roberts, 2011). Other studies on GPP or NPP of natural ecosystems (Cirino, Souza, Adams, & Artaxo, 2014;Rap et al, 2015;Urban et al, 2012) and agroecosystems (Niyogi et al, 2004;Xin et al, 2016) in response to diffuse radiation are based on flux measurements using eddy covariance techniques.…”

Maize Yield Potential and Density Tolerance

“…Although there is no evidence of this occurring in maize, as 4 to 18 yr of unchanging yields need to be recorded before yield plateaus become statistically significant (Grassini et al, 2013), it is quite possible that maize yields in the United States and Canada are experiencing or are nearing a plateau (Lobell and Azzari, 2017). Solar brightening is responsible for 27% of the on‐farm maize yield gains in the US Corn Belt observed between 1984 and 2013 (Tollenaar et al, 2016), calling into question the true contribution of genetic improvement during this timeframe. Concurrent with solar brightening is increases in the variation in GY observed both within and between fields (i.e., heterogeneity), with average yield differences more than doubling between the worst and best soils since 2000 (Lobell and Azzari, 2017).…”