Evaluation of Response of Onion and Tomato Crops to Deficit Irrigation and Evaluation of AquaCrop Model to Simulate Responses

Abstract

Investigating crop yields in response to water applications is resource-intensive. In this regard, modeling is a valuable approach for studying deficit irrigation strategies. An experiment at Melkassa Agricultural Research Center tested different irrigation levels at various onion and tomato growth stages, comparing 100%, 75%, and 50% ETc applications to assess the model's performance. A randomized complete block design was employed for the treatments; there were six treatments, and each treatment was replicated three times. The AquaCrop Model was calibrated using 100% ETc data on canopy cover and biomass, observed yield at the final, and validated to simulate onion and tomato yield and biomass at the final. The experimental results revealed that the highest yields, amounting to 5.75 tons/ha for onion and 8 tons/ha for tomato, were obtained from non-water stress treatment. Conversely, the lowest yields of 4.30 tons/ha for onion and 6.23 tons/ha for tomato were recorded when applying a 50 percent deficit irrigation strategy across all growth stages. The calibration results for both onion and tomato canopy cover and biomass simulations have a high degree of accuracy. For onion, the statistics included a ‘r’ of 0.99, a RMSE of 3.4 tons/ha, a NRMSE of 8.2%, an EF of 0.99, and a ‘d’ of 1 for canopy cover. The above-ground biomass calibration showed an ‘r’ of 1, an RMSE of 0.5 tons/ha, an NRMSE of 10.7%, an EF of 0.98, and a ‘d’ of 0.99. Similarly, for tomatoes, the calibration results indicated a high level of accuracy, with a canopy cover ‘r’ of 0.99, an RMSE of 4.4 tons/ha, an NRMSE of 8.8%, an EF of 0.98, and a ‘d’ of 0.99. The above-ground biomass calibration for tomato yielded an ‘r’ of 0.97, an RMSE of 0.6 tons/ha, an NRMSE of 9.2%, an EF of 0.98, and a ‘d’ of 1. The AquaCrop model successfully simulated the final dry yield for onion with an ‘r’ of 0.94 to 1, NRMSE of 1.5 to 4.3%, EF of 0.96 to 0.98, and ‘d’ of 0.95 to 0.98. The total biomass simulation showed good accuracy, with an ‘r’ of 0.94 to 0.97, a low NRMSE of 6.10 to 10.10%, a high EF of 0.95 to 0.98, and RMSE of 2.1 to 3.5 tons/ha. For tomato, the AquaCrop model also performed well, with a final dry yield simulation resulting in an ‘r’ of 0.96 to 0.98, an RMSE of 0.42 to 0.8 tons/ha, an NRMSE of 3.2 to 7.0%, an EF of 0.97 to 0.99, and a ‘d’ of 0.96 to 0.99. Total biomass simulation showed an r of 0.95 to 0.99, an RMSE of 0.4 to 0.92 tons/ha, an NRMSE of 5.6 to 10.50%, an EF of 0.96 to 0.99, and a ‘d’ of 0.94 to 1 for the study site. This field study indicated the crop's sensitivity to moisture stress during critical bulb and yield formation growth stages for both onions and tomatoes.