Estimation of Yield Response (Ky) and Validation of CropWat for Tomato under Different Irrigation Regimes at Melkassa

Abstract

CROPWAT is FAO computer programme that calculate crop water and irrigation requirements from a given climatic and crop data. Validated CropWat  model is useful for irrigation decision support system to help tomato growers. Field experiment was conducted at Melkassa Agricultural Research Center  to determine the optimal irrigation levels for maximum tomato production and to assess the effect of limited water supply on field grown tomato yield  and to estimate ‘yield response of tomato to soil water (Ky)’ and to validate CropWat irrigation model using the data for tomato cultivation during hot-dry  season conditions. Three irrigation scheduling levels such as 1) 100 % of crop water requirement (ETc) (Full irrigation) 2) 80% ETc (= 0.80 ETc) and finally 3)  60 % ETc (= 0.60 ETc) were used using drip irrigation replicated three times; the tomato was subjected to various levels of water stresses over whole  growth period. Yield data such as marketable, unmarketable and total fruit yield were collected at each harvesting and summed at the end of harvesting.  The analysis of variance showed that use of various irrigation depth brought significant effect (P< 0.01) on the marketable yield of tomato. However,  application of various irrigation depths did not bring significant difference (P< 0.05) on unmarketable fruit yield of tomato. Use of various irrigation depth  had a significant effect (P< 0.05) on the total fruit yield of tomato. The mean separation indicated that the highest fresh fruit yield was obtained  from full irrigation and the lowest was obtained from 60% irrigation. Thus, the total fresh fruit yield obtained from fully irrigated tomato plot exceeded  the fresh fruit yield obtained from tomato plot irrigated with only 60% of full irrigation water by 62.8%. The results showed that with decrease in the  amount of irrigation per application, there was a decrease in total fruit yield in tomato due to reduced uptake of water. The calculated yield response (Ky)  of tomato was 0.999 indicating that the yield reduction is directly proportional to reduced water use.CROPWAT irrigation model was validated using field  data, then modeling efficiency was found to be 94% indicating that the model has a potential to be use full as a decision support system to help tomato  growers.