Environmental drivers of wheat yield variability across China's production regions: Insights from field experiments

Wheat crops underpin contemporary global food security. Predominant wheat production zones in China include the Huang-Huai-Hai-Plain and the Mid-Lower Reaches of the Yangtze River, although climatic effects on productive potential across these regions vary markedly in space and time. Here, we conducted field experiments during the wheat season of 2015-2018 to examine environmental effects on growth, with fertilization and irrigation provided at levels ensuring that nutrient and water stress exposure was minimal. Yields in Huang-Huai-Hai-Plain and the Mid-Lower Reaches of the Yangtze River averaged 8950 and 4818 kg ha-1, respectively. Yield variation across regions was primarily related to spike number per unit area and grain number per spike. Maturity biomass was higher in Huang-Huai-Hai-Plain; this translated into higher grain yields. Lower temperature and longer growing duration between emergence and jointing in Huang-Huai-Hai-Plain afforded higher tillering and spike numbers, whereas higher growth rates from jointing to maturity resulted in higher biomass production in Huang-Huai-Hai-Plain compare with the Mid-Lower Reaches of Yangtze River. Growth rate, grain numbers and yield were positively correlated with the ratio of daily intercepted solar radiation to mean temperature during jointing to anthesis, termed photothermal quotient. Collectively, our results suggest that growth rate accounted for more variation in biomass production compared with growth duration, and the photothermal conditions in the Mid-Lower Reaches of the Yangtze River were restrictive for spike development and yield formation. Our results help disentangle drivers of crop growth through the development of agro-environmental conceptual frameworks, enabling a better understanding of yield variability in space and time.