Abstract:
AquaCrop is a computer based water productivity model used to predict growth, development and yield of
agricultural crops. Despite the wide application of the model in scenario analysis, it has not been used in zero
tillage. This study aimed to calibrate and validate AquaCrop model on wheat crop yield under conventional
and zero tillage practices for ASAL climatic condition of Laikipia County. Evaluation was based on field
experiments set up at Lengetia farm in Laikipia East sub-County. Field trials were carried out with two tillage
treatments, zero tillage (ZT) and conventional tillage (CT) and four varying sowing onsets dates namely early
(SD1), normal (SD2), late (SD3) and a control treatment with supplemental irrigation under normal sowing
dates (WTSD2). This was laid out in a randomized complete block design in split plot arrangement in three
replicates. Calibration was done using the control treatments while validation was done based on comparison
between simulated and observed data from the field trials. The model performance in simulating canopy
cover(CC %), biomass (B in ton/ha) and soil water content (SWC, mm) was evaluated using statistical indices
root mean square error (RMSE), Willmott’s index of agreement (d), coefficient of determination (R
2
) and
Nash-Sutdiffe model efficiency coefficient (EF). The value of R
2
of 0.95, 0.80 & 0.51 respectively for
calibration of CC, B and SWC were obtained for conventional tillage and R
2
of 0.88, 0.87 & 0.50 in validation.
In zero tillage, calibration was not satisfactory especially in simulating soil water content (R
2= 0.13). This was
attributed to the improvement in soil hydraulic properties through zero tillage practice. This limited the
model application in zero tillage hence the need for additional measures on improved hydraulic properties
of soil and crop response under Zero tillage.
