الفهرس 
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Abstract
An experiment was carried out at Dokki site - Central Laboratory for Agricultural Climate - Agricultural Research Center in Dokki, Giza Governorate, in the two successive agricultural seasons 2018 and 2019, for studying the assessment of different nitrogen levels (120 kg, 150 kg, 180 kg\feddan) in a complete randomized blocks design experiment on vegetative characteristics and production of potato as well as water footprint and crop water requirement. The obtained results can be summarized as follows:
Vegetative characters.
The highest potato vegetative growth characteristics (plant height, number of branches, wet and dry weight of shoots, number of leaves, leaf area, fresh and dry weight of leaves gave by the level of nitrogen fertilization 180 kg per feddan, while the level of nitrogen fertilization 120 kg per feddan observed the lowest values. The significant differences among the treatments were true during the two cultivated seasons.
The highest reading of total chlorophyll content (SPAD) recorded in the nitrogen fertilization treatment of 180 kg per feddan, while the lowest reading for chlorophyll was at the level of 120 kg per feddan of nitrogen.
Tuber characteristics and tuber yield.
The nitrogen fertilization level of 180 kg per feddan produced the highest significant values of number of tubers, specific gravity, marketable yield and total yield of potato, while the lowest significant results were recorded when nitrogen fertilization 120 kg per feddan was applied in both cultivation seasons.
The nitrogen fertilization 120 kg per feddan had the highest record of unmarketable yield of potato while the lowest was gave by 180 kg per feddan treatment.
Nitrogen contents (%) of potato leaves.
The highest nitrogen nutrient content for the tubers was recorded in the nitrogen fertilization level of 180 kg per feddan in the two seasons. The lowest results were at a nitrogen fertilization level of 120 kg per feddan in the two seasons.
Water footprint estimation
The crop water use
The crop water use is constant amount for all N treatments at the same season while differed from season 2018 to 2019 in respect to the water requirement calculation via estimation Et0.
The blue water footprint
The lowest significant blue water footprint result of potato were 99.9 and 99.2 m3/ton during the two cultivated seasons respectively, recorded by the treatment 180 Kg N / fed.
The nitrogen level of 120 Kg/fed gave the highest potato blue water footprint 116.9 and 115.5 m3/ton for the first and second seasons, respectively.
The gray water footprint
The nitrogen level of 120 Kg N / fed presented the lowest gray water footprint of potato with 181.5 and 184.1 m3/ton for the first and second seasons respectively.
The nitrogen level of 150 Kg N / fed illustrated an average values (in between both treatments of 120 and 180 Kg N / fed) of gray water footprint of potato during the both of cultivated seasons.
The nitrogen level of 180 Kg N / fed had the highest potato gray water footprint, measuring 232.5 and 237.2 m3/ton for the all seasons.
Water Footprint
The lowest value of water footprint was 298.4–299.6 m3/ton for first and second seasons, respectively, at a nitrogen level of 120 Kg/fed.
The nitrogen level 180 Kg/fed recorded the highest value of water footprint 332.4 and 336.4 m3/ton, during the both cultivated seasons, respectively.
- CONCLUSION
Needless to mention that the impact of increasing the N fertilization rate from 120 Kg/fad to 150 up to 180 Kg /fad demonstrated positive significant effect on the vegetative growth characteristics as well as potato yield parameters but the question is which N fertilizer rate that recorded the highest marketable yield of potato without any environment, public health and economic hazards under Egyptian conditions?
The answer of this question is expressing this study conclusion. The highest rate of N application (180 Kg / fed) gave the highest marketable potato yield and the lowest blue water footprint but there is a need to grey water about 2.4 times of blue water that led to presented the highest water footprint result.
On the other wise, for environmental issue that demonstrated in the lowest grey water footprint and total water footprint instead of marketable potato yield and blue water footprint, N application (120 Kg/fed) introduced the optimum choice. Also, the choice of N application (150 Kg / fed) is on the table in case of achieve acceptable marketable yield with less impacts on environmental.
These results gave the opposite side of using the high rates of N and its impacts on potato water consumption and the direct and indirect impacts on the environment.
The head quarter question is, what we need the potato yield or environment? Or to be more precise, the conflict between food production, sustainability and environment?