Accuracy of using carbon isotope in estimating water use efficiency of cereal and legume crops: a global perspective
ID: 613 / 282
Proposed Symposium Title: Accuracy of using carbon isotope in estimating water use efficiency of cereal and legume crops: a global perspective
Mutanda Maltase12, Vincent Chaplot3, Hussein Shimelis2, Kwame W. Shamuyarira2, Sandiswa Figlan1
Affiliations: 1 Department of Agriculture and Animal Health, University of South Africa, Florida 1709, South Africa. 2 School of Agricultural, Earth and Environmental Sciences, University of KwaZulu-Natal, Private Bag X01, Scottsville 3209, Pietermaritzburg, South Africa. 3 Institut de Recherche pour le Dévelopement (IRD), Laboratory of Oceanography and Climate, Experiments and Numerical Approaches (LOCEAN), UMR 7159, IRD/C NRS/UPMC/MNHN, IPSL, 75005 Paris, France.
Field assessments of crop water use efficiency (WUE) are resource-consuming since they require simultaneous assessment of the total amount of water assimilated by crops for biomass and/or grain production. Alternative methods exist, such as estimating the carbon isotopic ratio (13C/12C) of the crop’s leaf, aboveground biomass, or grain samples. There is limited information on the determinants of the accuracy of carbon isotopes in estimating water use efficiency between crop types and environments. Therefore, this study aimed to evaluate the extent to which the estimation of the 13C/12C ratio in crop parts constitutes an accurate proxy of WUE, globally. Data on observed WUE (WUEobs) were collated involving 518 experiments conducted worldwide on major cereals and legumes and compared with WUE estimates (WUEest) from carbon isotopes. The mean WUEobs amongst all experiments was 3.4g l-1 and the mean absolute error (MAE) was 0.5 g l-1 or 14.7% of WUEobs, corresponding to accurate predictions at p < 0.05. However, the percentage mean absolute error of observed water use efficiency (%MAE) estimated from grains was 3.6±11.5%, which was lower than the %MAE from aboveground biomass collected at harvest (3±22.8%). In addition, the %MAE increased from 1.1±5.1% for soybean, 1.6±7.2% for maize, 1.2±8.6% for rice, 1.8±12.1% for groundnut, 2.1±14.3% for cowpea, 2.3±16.2% for bush bean, 1.8±19.9% for wheat, 2.2±21.4% for barley to 6.3±39.3% for oat, only the later corresponding to significant errors. WUEest were, in all cases unbiased but slightly overestimated from 0.8% (maize) to 15.4% (oat). The accuracy in estimating WUE significantly decreased with the increase in soil clay content, with sand, showing a positive correlation of 0.3 with %MAE, but negatively correlated with the silt content (r = - 0.4).