Evaluation of AquaCrop Model in Wheat Production Under Zero and Conventional Tillage Practices in Laikipia, Kenya

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.