Increasing maize yields in Northeast China are more closely associated with changes in crop timing than with climate warming

An understanding of mechanisms that underlie the steady increase in crop yields over recent decades is important for promotion of future sustainable yield gains and maintenance of future food security. In this study, we coupled observational maize yield and climate variables based on crop development data from 1981 to 2009 to construct an empirical model that can resolve the separate and combined effects of climate and agricultural practices related to crop timing on maize yield in Northeast China (NEC), the largest spring maize-producing region of China. Climate warming contributed to approximately 15.6% of the trend for increasing yield over the 29 year period. The beneficial effects of climate warming on yield were due to increases in accumulation of temperatures between 10 degrees C and 30 degrees C (growing degree days, GDD), which positively contributed to 29.7% of yield and offset the -14.1% yield reduction caused by a trend involving increasing accumulation of temperatures above 30 degrees C (or extreme degree days, EDD). Adaptive improvements in crop timing practices (e.g. shifts in planting date and selection of later-maturity cultivars) further optimized the impacts of GDD and EDD during the entire growing season by exploiting more GDD during the reproductive phase and fewer EDD during the vegetative phase, thereby contributing to a yield gain of 25.4% over the period from 1981 to 2009. Taken together, climate warming and crop timing practices contributed to 39.4% of the maize yield increase since 1981. Yield losses due to climate warming were detected at only one site located in the southern part of the NEC region, where yield losses must be offset by positive effects of crop timing changes. The trends in maize yields presented here may provide guidance for effective adaptation options for maize production under conditions of continued climate warming.