Climate-Induced Yield Variability and Yield Gaps of Maize (Zea mays L.) in Low-Input Agricultural Systems.

There is a high demand for quantitative information on impacts of climate on crop yields, yield gaps and their variability in low input agricultural systems such as the sub-Saharan Africa. A multi-model crop growth simulation approach using two crop models, i.e. Decision Support System for Agro-Technology (DSSAT) and WOrld FOod STudies (WOFOST) was applied to characterize climate-induced variability and yield gaps of maize. The models were calibrated and evaluated with experimental data from the Central Rift Valley (CRV) in Ethiopia, which represents major cereal-based farming systems of the semi-arid environments of sub-Saharan Africa. Subsequently, a simulation experiment was carried out with an early and medium maturing maize cultivars using historical weather data (1984-2009) of three locations in the CRV. Yield gaps were computed as differences among simulated water-limited yield (model simulated rainfed yield potential), on-farm trial yields and average actual farmers’ yields.

Water-limited yield shows high inter-annual variability (CV 36%) and most of this variability is explained by the variation in growing season rainfall. The gap between average farmers yield and simulated water-limited yield ranges from 5 to 6.0 Mg/ha. The average farmers’ yields were about 1 to 3 Mg/ha lower than on-farm trial yields. In relative terms, average farmers’ yields are 28-30% of the water-limited yield and 44-65% of on-farm trial yields. Exploiting the gaps between yields achieved currently on farmers’ fields and those that can be achieved by using improved technologies, including climate risk management strategies, is a key pathway to feed the increasing population at local, regional and global scales.

 The study showed the need to invest in technology transfer and institutional arrangements for improving access to “best” agricultural practices as for instance practiced in the on-farm trials that yielded on average 50-73% of simulated water-limited yield.  It also demonstrated how the use of more than one model may provide some insight in uncertainty of model simulations.

Key word: WOFOST, DSSAT, Crop simulation, Water-limited yield, Yield gap