Responses of gross primary production of grasslands and croplands under drought, pluvial, and irrigation conditions during 2010-2016, Oklahoma, USA

Authors: DOUGHTY, RUSSELL - University Of Oklahoma; XIAO, XIANGMING - University Of Oklahoma; WU, XIAOCUI - University Of Oklahoma; ZHANG, YAO - University Of Oklahoma; BAJGAIN, RAJEN - University Of Oklahoma; ZHOU, YUTING - University Of Oklahoma; QIN, YUANWEI - University Of Oklahoma; ZOU, ZHENHUA - University Of Oklahoma; MCCARTHY, HEATHER - University Of Oklahoma; FRIEDMAN, JACK - University Of Oklahoma; Wagle, Pradeep; BASARA, JEFF - University Of Oklahoma; Steiner, Jean

Submitted to: Agricultural Water Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/3/2018
Publication Date: 4/18/2018
Citation: Doughty, R., Xiao, X., Wu, X., Zhang, Y., Bajgain, R., Zhou, Y., Qin, Y., Zou, Z., Mccarthy, H., Friedman, J., Wagle, P., Basara, J., Steiner, J.L. 2018. Responses of gross primary production of grasslands and croplands under drought, pluvial, and irrigation conditions during 2010-2016, Oklahoma, USA. Agricultural Water Management. 204:47-59. https://doi.org/10.1016/j.agwat.2018.04.001.
DOI: https://doi.org/10.1016/j.agwat.2018.04.001

Interpretive Summary: Sustainable food production requires knowledge of crop-specific responses to drought and pluvial events, and what role irrigation plays in those responses to changes in climate. To examine the responses of grassland, winter wheat, other C3 croplands, and C4 croplands to drought and pluvial events, this study selected a pilot study area in Oklahoma that was representative of irrigated and non-irrigated grasslands and croplands, and experienced the 2011 drought and 2015 pluvial events, and analyzed the sensitivity of gross primary production (GPP) for those land cover types during the drought and pluvial events. Results showed that GPP of grasslands and croplands responded differently to drought and pluvial conditions. How a certain crop type responds to drought was dependent on whether the land owner had access to irrigation. Irrigation-permitted croplands had higher mean GPP and smaller interannual variability during the drought, while non-permitted C4 croplands had the largest percentage (-41%) reduction in GPP from the 5-year reference mean. Responses of GPP for irrigation-permitted and non-permitted grasslands to drought and pluvial conditions were extremely similar. The study was not able to determine whether landowners did not exercise their right to irrigate grasslands or irrigation of grasslands had little influence on GPP due to lack of irrigation data. During the pluvial year 2015, GPP was significantly higher for grasslands, winter wheat, and non-permitted C3 croplands, but there was no significant difference in GPP for irrigation-permitted C3 croplands or non-permitted C4 croplands. However, GPP for C4 irrigation-permitted croplands decreased by 9%.

Technical Abstract: To accurately estimate carbon cycling and food production, it is essential to understand how gross primary production (GPP) of irrigated and non-irrigated grasslands and croplands respond to drought and pluvial events. Oklahoma experienced extreme drought in 2011 and record-breaking precipitation in 2015, thus providing an opportunity to study such changes in GPP for grasslands and croplands. This study analyzes annual GPP of irrigation-permitted and non-permitted grasslands, winter wheat, other C3 croplands, and C4 croplands in Caddo County of western Oklahoma from 2010 through 2016. For each land class, annual GPP from the 2011 drought and pluvial 2015 were compared with mean GPP from the other 5 years of the study period. The results show that for the 2011 drought: 1) non-permitted C4 croplands had the largest percentage decrease (-41%) in GPP from the 5-year reference mean, but irrigation-permitted C4 croplands had no significant decrease; 2) GPP was significantly lower than the 5-year reference mean for all non- C4 vegetation types, regardless of water rights; 3) GPP for non-permitted lands were more affected by drought than irrigation-permitted lands, except for grasslands, which had similar percentage reductions in GPP (-35%). Results for the pluvial year 2015 indicate that: 1) GPP was significantly higher for grasslands, winter wheat, and non-permitted C3 croplands than the 5-year reference mean; 2) there was no significant difference in GPP for irrigation-permitted C3 croplands or non-permitted C4 croplands; and 3) GPP for C4 irrigation-permitted croplands was 9% lower than the 5-year reference mean.