Effects of environmental and management factors on worldwide maize and soybean yields over the 20^th and 21^st centuries

Abstract. The land process model, ISAM, is extended to accurately simulate contemporary soybean and maize crop yields, and estimate changes in yield over the period 1901–2100 driven by past and future changes in environmental factors – atmospheric CO₂ level ([CO₂]) and climate (temperature and precipitation) – and management factors – nitrogen fertilizer and deposition, irrigation, and crop harvest areas. Over the 20^th century, each of these factors contributes to the increase in global crop yield with increasing nitrogen fertilizer application the strongest of these drivers for maize and increasing [CO₂] the strongest for soybean. Over the 21^st century, two future scenarios – RCP4.5-SSP2 and RCP8.5-SSP5 – of the environmental and management factors are modeled to estimate their influence on future crop yield. For both crops under both scenarios, changing climate drives yield lower, while rising [CO₂] drives yield higher. For soybean, the negative climate effect is more than offset by the other drivers – particularly the increase in [CO₂] – leading to an increase in global soybean yield by the 2090s. For maize, combined negative climate and harvest area effects are offset in RCP4.5-SSP2, which has continued growth in nitrogen fertilizer application, leaving global yield roughly unchanged. However, in RCP8.5-SSP5 maize yield declines since this scenario has greater warming of climate and weaker nitrogen fertilizer application than RCP4.5-SSP2. The model also projects differences between geographical regions; notably, higher temperatures in tropical regions limit photosynthesis rates and reduce light interception by accelerating phenological development in both crops, particularly for RCP8.5-SSP5 and for soybean.