الفهرس 
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Abstract
This experiment was carried out during three successive seasons of 2003, 2004 and 2005 on Balady mandarin trees onto sour orange rootstock in El- Wahab orchard situated at Behaira Governorate where the soil is sandy. Drip irrigation and fertigation systems were followed in this orchard.
The objective of this study was to examine the effect of water quantities applied via drip irrigation as well as levels and frequencies of N applied via fertigation on vegetative growth, yield as well as physical and chemical characters of Balady mandarin fruits.
The experiment included the following 64 treatments from three factors :
1-The first factor consisted from four levels from water quantities applied via drip irrigation namely 16, 20 , 24 and 30 m3 / tree / year .
2-The second factor comprised from four levels of N applied via fertigation, namely 400 , 600 , 800 and 1000 g N/ tree/ year.
3-The third factor contained four levels of N fertigation frequencies namely 21, 23, 25 and 27 doses / year. Each treatment replicated three times , one tree per each.
The experiment was set up in completely randomized block design in a split – split arrangement. The four quantities of water, the four levels of N and the four N frequencies occupied the main, sub, and sub- sub plots, respectively.
Four evaluating the effect of quantities of water applied via drip irrigation as well as the levels and frequencies of N added via fertigation on growth and fruiting behaviour of Balady mandarin trees, the following parameters were recorded :
1-Vegetative growth characters namely shoot length , number of leaves/ shoot and average leaf area in the Spring growth cycle.
2-Percentages of N, P and K in the leaves from non- fruiting shoots.
3-Percentages of initial and final fruit setting.
4-Yield expressed in weight (kg.) and number of fruits/ tree.
5-Physical characters of fruits namely fruit weight (g.) and dimensions (height and width in cm.) as well as fruit peel weight and thickness (cm.)
6-Chemical characters of fruits including total soluble solids %, total acidity %, total soluble solids / acid, reducing %, and total sugars % and vitamin C content ( mg/ 100 ml juice)
The nearly the same results obtained in the three seasons could be summarized under the following main topics.
1-Vegetative growth characters:
Increasing water quantities applied via drip irrigation from 16 to 30 m3/ tree was followed by a progressive stimulation on Spring shoot length, number of leaves per shoot and leaf area in the Spring growth cycle. A slight promotion on these growth characters was observed among the higher two amounts of water namely 24 and 30 m3/ tree/ year.
These growth characters were gradually tended to stimulate with increasing levels from 400 to 1000 g N / tree and frequencies from 21 to 27 doses of N fertigation . Increasing levels from 800 to 1000 g N/ tree and frequencies from 21 to 23 doses of N fertigation failed to show measurable influence on these growth aspects.
The maximum values of growth characters were recorded on the trees received 30 m3 water / tree / year via drip irrigation and fertigated with N at 1000 g N/ tree at 27 doses annually.
2-Percentages of N, P and K in the leaves.
Percentages of N, P and K in the leaves were increased gradually with increasing the amount of water applied via drip irrigation from 16 to 30 m3/ tree / year. They were slightly improved when the amount of water was raised from 24 to 30 m3/ tree / year.
Increasing N fertigation levels from 400 to 1000 g N / tree was accompanied with increasing N % and decreasing both P % and K % in the leaves. The three essential element were gradually tended to enhance with increasing N fertigation frequencies from 21 to 27 doses per year. Splitting the amount of N into doses above 21 ( i.e. 23, 25 or 27 doses) gave the same results. Therefore, dividing the amount of N fertigation into 23, 25 or 27 doses was necessary to enhance nutritional status of the trees.
3-Percentages of initial and final fruit setting and yield.
Percentages of initial and final fruit setting, yield (kg.) and number of fruits per tree were positively affected by increasing the water quantities applied via drip irrigation from 16 to 30 m3/ tree / year. The promotion was associated with increasing the amount of water applied via drip irrigation. Meaningless promotion was observed on these parameters when water per tree was increased from 24 to 30 m3/ tree / year. Therefore, from the economical point of view the optimum amount of water to be applied via drip irrigation for obtaining an economical yield was 24 m3 water/ tree/ year.
Increasing levels and frequencies of N fertigation was accompanied with promoting percentages of initial and final fruit setting, yield and number of fruits / tree Increasing levels of N fertigation from 800 to 1000 g N/ tree had no considerable effect on these parameters, therefore, the recommended rate was 800 g N/ tree. The three N fertigation frequencies namely 23, 25 and 27 doses behaved similarly in this connection. Therefore, application of N must be done at 23, 25 or 27 doses through using it via fertigation in citrus orchards.
From economical point of view, it is recommended to irrigate Balady mandarin trees growing under sandy soil with 24 m3 water / tree/ year as well as fertilizing them with N via fertigation at 800 g / N at 27 doses annually for obtaining satisfactory promotion on yield.
4-Fruit quality :
Increasing water quantities applied via drip irrigation from 16 to 30 m3 / tree/ year was followed by enhancing fruit quality in terms of increasing fruit weight and dimensions, total soluble solids %, total soluble solids / acid, total and reducing sugars and ascorbic acid content and in decreasing fruit peel weight and thickness and total acidity %. There was a slight promotion on fruit quality between using 24 and 30 m3 water / tree / year levels via drip irrigation.
Increasing levels and frequencies of N fertigation was followed by an obvious and remarkable promotion on fruit quality. However, physical characters were not improved materially when levels of N was increased from 800 to 1000 g N/ tree. Also, chemical quality parameters were impaired when N levels were increased from 800 to 1000 g N / tree , So the selected rate was 800 g N / tree. Dividing N amounts into 23- 27 doses considerably improved fruit quality compared to using N at 21 doses .
The best favourable effects on fruit quality were obtained on the trees irrigated with drip irrigation at 24 m3 water / tree / year and fertigated with 800 g N / tree at 27 doses.
CONCLUSION:
The best results with regard to yield and fruit quality were obtained due to supplying Balady mandarin trees growing under sandy soil with water at 24 m3 tree / year via drip irrigation and fertigating with N at 800 g N / tree at 27 doses.