Modeling the impact of extreme climate events on productivity of perennial bioenergy feedstocks in the American Midwest

Abstract:

Widespread drought in the American Midwest in 2012 and 2013 resulted in significant crop loss and economic impacts to the region. Climate projections for the region indicate increased future moisture variability and increased intensity of extreme events, including severe weather and drought. Row crops (maize and soybean) in this region are replanted on an annual basis, eliminating many legacy effects of the previous year’s drought. The unfertilized perennial grass Miscanthus x giganteus, planted as an alternative to maize for the production of bioethanol, showed both direct and legacy effects of drought, as the first year of the drought in 2012 resulted in a 32% reduction in yield compared with the previous two years, and in 2013 yield fell by 19% over 2010-2011. In 2014, nitrogen fertilizer (56 kg N/ha) was applied to half of mature (6-yr) miscanthus stands in an effort to improve post-drought yield. Plant growth increased with fertilizer from the earliest measurement stage, with maximum effect observed in August of 2014 (2.1-fold over unfertilized). Annual measurements of aboveground biomass from fertilized miscanthus from 2014-2018 show a 1.8-fold average increase over unfertilized. The introduction of fertilizer to previously unfertilized 11-yr miscanthus in 2019 resulted in smaller but significant biomass increases over the previous year, but 36% below miscanthus with 5 years of fertilization, indicating that timing of fertilization for long term regimes has an impact on sustained yield improvement. Model predictions of perennial crop productivity incorporating dynamic responses to climate disturbances show a significant reduction in yield estimates with repeated extreme weather events. Simulations of routine nitrogen additions reduce the impact of severe drought and help restore crop productivity indicating that nutrient availability and assimilation are strong determinants of the biome water use efficiency, driving crop resilience to water stress.