Application and evaluation of aquacrop, dssat and simple model in modelling yield water use of selected underutilised cereal crops.
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Date
2021
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Abstract
The study compared yield, biomass, and water use (WU) for maize, sorghum, and millet
simulated using three crop models of varying complexity: AquaCrop, DSSAT and the SIMPLE
model. The hypothesis was that there is no significant difference between simple and complex
models of estimating yield, biomass and WU. A standard set of crop parameters was used to
develop crop files for all three models. Similar soil, climate and management descriptions
attained from the Ukulinga Research Farm were used across the models. Six general circulation
models (GCMs) were used as climate input data to model past, present, mid-, and late-century
climate change impacts on cereal crops. The effect of irrigation (as a management practice) on
yield and water use was assessed using the mid-century projections. The performance of the
three models was observed to be statistically different. Based on the mean bias error, all models
overestimated yield, but the lowest overestimation was with AquaCrop (0.22 t/ha) followed by
DSSAT (0.24 t/ha) and the SIMPLE model (0.69 t/ha). Other statistical indicators, viz., RMSE
and R2, illustrate that the simulation of yield and WP in AquaCrop was more satisfactory than
DSSAT and the SIMPLE model. Across all the time scales, it was observed that AquaCrop
simulated the highest yield and biomass, and the SIMPLE model simulated the lowest yield
across the GCMs, which were inconsistent. Applying a higher amount of irrigation at more
frequent intervals resulted in higher yield, biomass and WP. AquaCrop showed the highest
simulated mean yield for maize (8.34 t/ha), millet (6.86 t/ha) and sorghum (5.28 t/ha). Highest
WP was observed under AquaCrop for maize (21 kg/ha/mm) and millet (15.10 kg/ha/mm), the
SIMPLE model for sorghum (13.37 kg/ha/mm). The study confirms that DSSAT requires
relatively more input data but does not always perform more satisfactorily. The SIMPLE model
requires fewer input requirements than AquaCrop and DSSAT; however, it is less sensitive to
management changes. AquaCrop had relatively incomparable results to DSSAT and the
SIMPLE model and was observed as the most suitable model for simulating yield, biomass,
and WU of the selected cereal NUS under climate change and irrigation management scenarios.
Before their application, it is essential to calibrate crop growth parameters for local conditions
or use parameters from local field studies when applying complex crop models such as DSSAT
specifically for marginal environments, such as South Africa. On the other hand, AquaCrop
performed reasonably well with minimal input requirements, confirming its application in datalimited
and marginal environments. However, it is recommended that there must be calibration
for all the models using inputs specific to locations.
Description
Masters Degree. University of KwaZulu-Natal, Pietermaritzburg.