الفهرس 
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Abstract
The current study was an attempt to investgate the possablities to improve the irrigation water productivity of one of the tomato crop as one of the most important vegetable crops in Egypt. The main objective of this study is to investgate the current and future potinal possiablites of using deficit irrigation to improve the crop-water productivity of the tomato crop, as one of the most important vegetable crops in Egypt. This objective coud be achived by following the three steps: (i) Investigate the actual effect of applying different deficit irrigation schemes on the growth parameters and the yield of tomato crop, (ii) Conduct a calibration of AquaCrop model to simulate the effect of deficit irrigation schemes on tomato crop, under the local current conditions, and (iii) Assess the impact of climate change on tomato crop under full irrigation and different deficit irrigation schemes. The experiment investigated five irrigation treatments, as folloing: (i) 100% ETc [T100], (ii) Application of deficit irrigation level 80% ETc at all crop growing stages [TC80], (iii) Application of deficit irrigation level 80% ETc at initial and maturity crop stages only [TS80], (iv) Application of deficit irrigation level 60% ETc at all crop growing stages [TC60], (v) Application of deficit irrigation level 60% ETc at initial and maturity crop stages only [TS60]. The study used the experimental and the analytical approaches based on simulation model AquaCrop, and the results of the study could be summarized as the following:
The effect of applying different deficit irrigation schemes on the growth parameters and the yield of tomato crop
Among the investgated deficit irrigation schems, applying diffecit irrigation schems of 80% ETc could reduce the amount of the irrigation water by 20% when the deficit applied at all crop growing stages, coupled with a yield reduction of about 18%, and a slight increase in water productivity of about 7%. Whereas the same deficit level could save about 14% of the applied water when it applied only at initial and maturity growth stages only, and decrees the crop yield by 5%, which give the highest WP of 1.82Kg/m3 . Those two schemes gave the best results among the other deficit schemes.
The water shortage significantly improved TSS as compared to full irrigation treatments. Similarly, the vitamin C content for tomato fruit was greater under water stress conditions. Statistical differences in pH among treatments were less clear than for TSS and vitamin C content.
The maximum energy consumption was (8000 MJ/ha) for T100 treatment, while the minimum energy consumption was (4900 kw/ha) for TC60 treatment. This due to low irrigation water applied during the growing season.
Calibration of AquaCrop model to simulate the effect of deficit irrigation schemes on tomato crop production
The calibration process of AquaCrop is based on adjusting some crop parameters which represent the crop growth cycle, and the thresholds of stress factors. The calibration process based on the comparison between the observed and the indicated values of the five production parameters of CC, biomass, yield, and HI.
The results show that the AquaCtop model is over predicting the CC values at the initial stage under all irrigation treatments, but it gives a good performance to simulate the CC values for the other crop growth stages. As well as, the AquaCrop model reveled a very good performance in simulating the tomato crop biomass, the crop yield and the harvest index (HI). The good performance reflects the good quality calibration process that was conducted by using the field data of the two seasons 2015/2016 and 2016/2017 experiment.
The impacts of climate change on tomato crop production under full irrigation and different deficit irrigation schemes
The results show that the length of the crop growth cycle decreasing by 2050s for all irrigation treatment due to the increasing in temperature by an average of 0.4 to 0.8 °C for RCP4.5 and RCP8.5, respectively. Whereas, the rate of maturity is relatively faster in high emission scenario (RCP8.5) as opposed to low emission scenario (RCP4.5). Furthermore, thus, on average, the number of days between transplanting and maturity for tomatoes is expected to be reduced by about 3 –11 days by the end of 2050s, compared to reference period values.
The ETc values are decreasing by 2050s for all water treatment, as a result for the addressed decreas on the crop growth cycle length, the growing temperature increase stress.
Under full irrigation treatment, the temperature increase has a negative effect of the tomato crop yield. The irrigation treatments TC80 and TS80 have the higher trends of tomato yield increase under RCP8.5 scenario, with values for 2030s of 5.3% and 4.6% above the reference period values, for the two irrigation treatments, respectively. Moreover, under the same scenario and by 2050s, the tomato crop yield of the same irrigation treatments is expected to increase by 0.5% and 1.2% above the reference period values.
In conclusion, the combination between irrigation scheduling and deficit irrigation level of 80% could improve the water productivity to levels near to the optimal level, especially with deficit level of 80% applied at the early and the late stages of crop development, which provide water saving amount up to 14%.
from the previous results a number of recommendations could be addressed:
- Under the conditions of limited water resources, deficit irrigation could present some good possibilities for tomato crop production, in terms of water saving and water productivity improvement.
- AquaCrop model reveled a good performance in simulating tomato crop responses to deficit irrigation. The quality of the simulation performance is highly related to the quality of the data used in the local calibration process.
- Conducting more field trials aiming to produce and collect high quality field data, could strongly help in conducting more simulation studies by using AquaCrop model, to investigate several management on-farm options to improve water productivity of the important crops.
- Study the effect of deficit irrigation on mechanical, physical parameters and mechanical damage on tomatoes.
- Make an economical analysis for applying the deficit irrigatin in Egypt.