الفهرس 
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Abstract
This investigation aims to study the optimum irrigation interval for wheat crop to obtain maximize yield and save irrigation water which can be used to cultivate a new areas. In addition, to optimize nitrogen and potassium sources and levels. So, wheat cultivar (Sids 7) was planted in Giza Agricultural Research Station (Agricultural Research Center) during the two successive growing seasons of 1998/99 and 1999/2000. The experiment was laid out in split- split plots design with three replicates. The main plots were devoted to irrigation intervals and the sub plots were assigned to nitrogen sources and levels, and the sub- sub plots for potassium levels. However, 24 treatments combined of three irrigation duration i.e., 15, 25 and 35 days, 4 nitrogen treatments (2 for N sources i.e., ammonium nitrate and sulphate in two levels i.e. 125 and 150 kg N/fed), and 2 potassium levels i.e., 75 and 100 kg IC/fed). The obtained results could be summarized in the following:-
1- Wheat water relation parameters:-
1.1. Seasonal actual evapotranspiration (ETa) gradually increased as the available soil moisture increased in the root zone of plants, while subjecting wheat plants to soil water deficit caused decrease in ETa. On the other hand, ETa was increased for the high level of nitrogen as compared with the low one under the two sources. Besides, the ammonium nitrate encourages wheat plants to absorb more water from the soil. Moreover, enhancing potassium level is followed by the increase in ETa values.
1.2. The maximum monthly ETa values were recorded during January and associated by NH4NO3 additions comparing with
that of (NH4)2SO4. At the same time, monthly ETa values were increased as potassium level increased.
1.3. The greatest soil moisture extraction values within the surface root zone (0-30 cm) was obtained with 25 day irrigation interval with the application of 150 kg N/fed as a form of N1-14NO3 and 100 kg K/fed.
1.4. The maximum water use efficiency (WUE) was pronounced at 25 days irrigation intervals and the application of 150 kg N/fed as NH4NO3 form and the addition of 75 or 100 kg K/fed.
1.5. The highest values of ET. and ETerop were obtained by using the Modified Penman formula while the lowest one was found by using Doorenbos-Pruitt formula.
1.6. The Modified Penman formula was superior in calculating ETcrop for wheat in Middle Egypt (i.e., Giza region) followed by Penman-Monteith compared with the value of the Doorenbos-
Pruitt formula.
2. Effect of water regime and mineral fertilization on wheat yield and its chemical composition:-
a)The greatest grain yield was recorded at 25 day irrigation interval, while the lowest one was remarked at 35 day. The relative decrease in grain yield was 36 and 17% at 35 and 15 day irrigation intervals, respectively. The extent of decrease due to water regime was most pronounced at low rate of both nitrogen and potassium fertilizers especially when ammonium sulphate was used as a nitrogen source.
b)Enhancing irrigation periods was followed by a decrease in the straw yield. The highest decrease (24.5%) was obtained at 35 day irrigation interval, while the lowest one (17.3%) was achieved at 25 day irrigation intervals. Moreover, the lowest straw yield was observed at low rates of nitrogen and potassium
treatments and also when (NH4)2SO4 was used as a nitrogen fertilizer.
c) The highest No. of wheat spike/m2 was found at 25 day irrigation intervals and decreased at 15 and 35 day irrigation periods, respectively by 4.4 and 6.68% compared to 25 day irrigation intervals. The extent of decrease due to water regime was recorded at low rate of nitrogen especially with ammonium nitrate, while the opposite trend was observed with increasing potassium rate.
3. The nutritional value of Wheat yield:
a)The consequence of water stress (increasing irrigation periods) is significantly decreased nitrogen content in wheat grains by means of crude protein. In addition, the nitrogen percentage was increased with the application of ammonium nitrate as compared by ammonium sulphate at 15 and 25 day irrigation intervals. The opposite was remarked at 35 day irrigation period. Also, N% increased significantly with the enhancing of potassium doses.
b)Phosphorus content in wheat grains was decreased by increasing irrigation duration. The relative deficit in P% was 4.76 and 14.3% at 25 and 35 day irrigation intervals, respectively compared to 15 day irrigation period. On the other hand, Phosphorus content was increased with the application of ammonium sulphate. Moreover, P% markedly increased with the increase in potassium doses.
c)Potassium content in wheat grains was negatively affected by the irrigation periods increase (water stress). The relative decreases in K content were 21.7 and 42.2% at 25 and 35 day irrigation intervals, respectively when compared with those of 15 day duration. Also, the content of K in wheat grains was higher in the treatment received NH4NO3 as opposite of that
Summary and conclusions 96
received (NH4)2804. Besides, its content was not significantly affected by increasing the doses of potassium fertilizer applications.
d)Water stress was significantly decreased nitrogen content in wheat straw. The relative decreases were 3.4 and 20.1% at 35 and 15 day irrigation intervals, respectively comparing with 25 day irrigation period. In addition, N% was greater when ammonium sulphate was applied. Moreover, the content of nitrogen in wheat straw was slightly increased by increasing potassium fertilizer additions.
e)The increase in irrigation periods was markedly increased phosphorus content in wheat straw. The relative decreases in P% were 35.7 and 14.3% at 15 and 25 irrigation intervals, respectively compared to 35 day irrigation period. Phosphorus content in wheat straw yield was higher when ammonium sulphate was used. In addition, the high doses of potassium fertilizer not increased P% in wheat straw yield.
f)Water stress was significantly decreased potassium content in wheat straw yield. The relative decrease in K content was 4.45 and 5.48% at 15 and 25 day irrigation intervals, respectively comparing with 25 day irrigation period. The content of K in wheat straw was higher when ammonium nitrate was used and clearly increased by increasing the amount of K2SO4 fertilizer.