An independent method of deriving the carbon dioxide fertilization effect in dry conditions using historical yield data from wet and dry years

Accurate estimates of the fertilization effect that elevated carbon dioxide CO₂] has on crop yields are valuable for estimation of future crop production, yet there is still some controversy over these estimates due to possible CO₂‐by‐water‐status interactions in chamber studies and the difficulty of conducting field experiments with elevated CO₂]. This study presents a new method to estimate the CO₂ fertilization effect (CFE) in dry conditions (CFE_dry), based on a combination of historical yield and climatic data and field experiments that do not require elevated CO₂]. It was estimated that approximately 50 years of increasing CO₂] (i.e., a 73 ppm increase) resulted in a 9% and 14% improvement of yield in dry conditions for maize and soybean, respectively, which are similar to estimates derived from free air CO₂ enrichment (FACE) studies. The main source of uncertainty in this approach relates to differential effects of technology trends such as new cultivars in wet vs. dry years. Estimates of this technology–water interaction can be refined by further experimentation under ambient CO₂], offering a cost‐effective path for improving CFE estimates. The results should prove useful for modeling future yield impacts of climate change, and the approach could be used to derive estimates for other species using relatively simple yield trials.