Sensitivity of gross primary production of irrigation-permitted and non-permitted grassland and croplands to drought and pluvial conditions during 2010-2016

Abstract

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 conditions. Oklahoma experienced extreme drought in 2011 and record-breaking precipitation in 2015, thus providing an opportunity to study such changes in GPP of 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 the combined, 5-year mean GPP from the other 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 mean, but irrigation-permitted C4 croplands had no significant decrease; 2) GPP was significantly lower than the 5-year mean for all non-C4 vegetation types, regardless of water rights; 3) non-permitted lands were more sensitive to 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 mean; 2) there was no significant difference in GPP for irrigation-permitted C3 croplands or non-permitted C4 croplands; 3) GPP for C4 irrigation-permitted croplands was 9% lower than the 5-year mean.