Analysis of reason for recent slowing maize yield increase under climate change in China

Abstract: China's maize yield has demonstrated a slowing growth since the end of last century, which has received great concerns for policy makers and agricultural scientists. Reasons for such phenomena are usually ascribed to decreasing fertilizer efficiency, land degradation, decreasing technology inputs such as new crop varieties, and climate change. However, none of the reasons has been clearly investigated and quantified to date, particularly at a very regional scale. Here a gridded and time series database of maize yield, areas, irrigation, fertilizer application, we apply an ensemble empirical mode decomposition (EEMD) analysis and examine the contribution of each factors on past yield growth and their changes along time. We discover that the slowing yield growth has been experienced at the whole China and 15 provinces (autonomous regions, municipalities) in 1981-2008. Based on Cobb-Douglas production function, we create multiple linear regression models for the whole country and the 10 provinces that exhibits slowing yield increase, to isolate the contributions of fertilizer, irrigation, other physical inputs and climate on past maize yield increase. Results showed, at national scale, 1) maize yield was significantly correlated with fertilizer, irrigation, other physical inputs and climate factors during 1981-2008. Maize yield was significantly promoted by inputs of fertilizer, irrigation and others, with a 1% increase of these investments increasing maize yield by 0.39%, 0.06% and 0.04%. Among climate factors, change of precipitation increased maize yield, with a 1% increase in precipitation promoting maize yield by 0.21%. Whereas temperature and cloud cover had negative effects on maize yield change, a 1% increase in temperature and a 1% decrease in solar radiation would decrease maize yield by 0.99% and 1.04% respectively. 2) Past increase of fertilizer application amount contributed most to past yield increase of maize (70.24%), followed by irrigation (9.44%), and other physical inputs (5.43%). Within all climate drivers, increase of temperature reduced maize yield by 1.98%, while decrease in precipitation and solar radiation increased maize yield by 1.08% and 4.72%. 3) Increased fertilizer application significantly increased the production in Northern spring maize region and Huang-Huai-hai summer maize region. Irrigation had positive effects in Northern spring maize region. The other physical inputs had significantly positive effects in Huang-Huai-hai summer maize region. For climate drivers, increase of temperature could promote maize yield significantly in Northern spring maize region and Huang-Huai-hai summer maize region. The reducing solar radiation had significantly negative effects on maize yield in two maize producing regions. Although statistic model is able to isolate the contribution of various factors, it's accuracy depends on the training date and the models that have been selected. Our results only focus on the major factors that affecting China's maize production, which to some extent limits its explanation ability as many other factors such as environmental degradation, pest and diseases, labor loss have started to affect the national crop production. Nevertheless, our results are consistent with previous studies showing that fertilizer is the major player for past maize yield growth, while its decreasing contribution has caused the recent slowing the maize yield increase. Climate change is becoming an important factor in fluctuating the production and affecting the changing trends.