الفهرس 
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Abstract
The present study involved two separate experiments carried out at Dakhla, New Valley Governorate. The aim of the first experiment was to evaluate the growth, chemical composition and wood properties of six woody trees ( Eucalyptus citriodora, Cassia fistula, Robinia psedoacacia, Ceratonia siliqua Cupressus sempervirens and Taxodium distichum) irrigated under sewage irrigation system along 24 month- period ( May 2003- May 2005). In the second experiment, the response of Albizia lebbeck seedlings to irrigation treatments (sewage water/ normal water mixture at different ratios) and gibberellic acid concentrations in terms of vegetative growth and total chlorophylls content was examined.
The most important results for both experiments are summarized as follows:
First Experiment:
Vegetative Growth:
Plant height of the four broad- leaved seedling species (Eucalyptus citriodora, Cassia fistula, Robinia psedoacacia, Ceratonia siliqua) and the two needle like leaves seedlings species (Cupressus sempervirens and Taxodium distichum) was gradually increased from the beginning of the experiment, May 2003, until the end of the experiment, May 2005. The tallest seedlings were recorded for E. citriodora (7.77 m), followed by R. psedoacacia (5.58 m) and C. fistula ( 3.93 m), While C. sempervirens gave the shortest seedlings.
The increasing rate %, for all six tested species in plant height, was sloping downward, as the highest increasing % was occurred in the first period ( 0-6 months) , while the least one was occurred in the fourth period ( 18- 24 months). Among different plant species, the highest increasing % in plant height, in the 0-6 period, was recorded for R. psedoacacia and E. citriodora and the least increasing % was recorded for C. sempervirens and T. distichum. In the last growth period (18- 24 months), however, the highest increasing % was due to E. citriodora and C. fistula and the least one due to R. psedoacacia and C. sempervirens.
Stem diameter, for the six pre-mentioned wood, plant species took the same trend like that of plant height. It was gradually increased up to end of the 2- years experiment. The thickest stem diameter in descending order, was recorded for E. citriodora ( 9.29 cm), R. Psedoacacia ( 8.04 cm) T. distichum ( 6..29 cm), C. fistula (4.44 cm), C siliqua ( 3.76 cm) and C. sempervirens ( 2.69 cm). The increasing rate % in stem diameter was also gradually reduced for all species toward the end of the 2- years experiment. Meanwhile, the highest increase % in stem diameter was recorded for E. citriodora and R. psedoacacia in the first and second periods ( 0-6 and 6- 12) and for T. distichum and C. siliqua in the third and fourth periods (12- 18 and 18- 24). Concerning stem diameter at the end of experiment at different heights i.e. at base, ¼, ½ , ¾ and at breast height ( BH), the highest valves were given by E. citriodora , R. psedoacacia and T. distichum .
In regard to stem fresh weight, as well as, branches and leaves fresh and dry weights, for the six plant species , at the end of the experiment, E. citriodora, considerably , took the lead , followed by R. psedoacacia and T. distichum. Such three plant species gave 23.67, 10.13 and 3.010 kg respectively for stem fresh weight; 6.330, 5.390 and 2.120 kg respectively for branches fresh weight; 3.084, 2.520 and 0.744 kg respectively, for branches dry weight; 9.680, 3.610 and 2.480 kg, respectively for leaves dry weight. The lowest values, however, were given by C. semperivirens (0.690, 0.393, 0.162 , 0.560 and 0.209 kg, respectively for stem F.W. , branches F.W. , branches D.W., leaves F.W. and leaves D.W.