الفهرس 
Effect of sowing dates
MATERIALS AND METHODSOnly 14 pages are availabe for public view
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Abstract
Two field experiments were carried out at at the Experimental Station of Agricultural Production and Research Station, National Research Centre, El Nubaria region, El Behaira Governorate, Egypt during the summer seasons of 2014, 2015 to study the productivity of sunflower cv. Sakha 53 under heat and water stress and reduced the harmful effect of those stresses by using an antioxidant such as ascorbic acid
Experiment included the following factors: -
a- Sowing date
1- 21st April.
2- 21st May.
3- 21st June.
b- Irrigation levels applied based on crop evapotranspiration (ETc) as follow:
1- Irrigation at 70% of ETc.
2- Irrigation at 85% of ETc.
3- Irrigation at 100% of ETc.
c- Ascorbic acid
1- Control (Tap water and Tween20).
2- Ascorbic acid (sprayed three times at 30, 40, 50 days after sowing and the concentration of Ascorbic acid was 150 ppm / time and Tween 20 added to the spray solution).
The experimental design was a split-split plot design with four replications. Main plots were occupied by the sowing date treatments, while the irrigation levels were distributed in the sub-plot and antioxidants treatments in sub sub-plot. Experimental unit area (sub sub-plot) was 12.25 m2. Seeds were sown in hills (3-5seeds in each hill) spaced 20 cm apart on the ridge. Plants were thinned at one plant per hill after 15 days from sowing date. In the both seasons, the previous cultivated crop was wheat. The cultural practices were followed as recommended for sunflower production in the region of the experiment.
The results obtained can be summarized as follows:
I. Physiological traits
1. Chlorophyll a and total chlorophyll (Ch a + Ch b) contents were the highest, proline value was the lowest in leaves of plants sown in May.
2. Each decrease in irrigation water amount resulted in increasing proline content but decreasing all other physiological traits.
3. Ascorbic acid (AsA) spraying enhanced chlorophyll a, chlorophyll b, total chlorophyll and carotenoids but caused reduction in proline content compared to the control.
4. sowing sunflower in May x irrigation with 100% of water requirement (i.e. ET100%) recorded the maximum values of leaf chlorophyll a, chlorophyll b, total chlorophyll and carotenoids, while the minimum values were detected when sowing in April x 70% of irrigation requirement (ET70%).
5. Sowing in May and receiving AsA caused marked increment in leaf chlorophyll contents (a, b, and a+b) but decrement in proline level, while carotenoids didn’t affect.
6. Applying ET100% x AsA(+) caused the highest values of chlorophyll a, chlorophyll b, total chlorophyll while lower proline content compared to other interaction treatments.
7. The maximum increases in Ch a, Ch b, and Ch a + Ch b contents were achieved through sowing sunflower in May x ET100% x AsA(+).II. Growth traits
8. Sowing in 21-May led to enhancing sunflower growth as obvious in achieving the highest values of all growth traits surpassing those of the rest sowing dates (21-April and 21-June).
9. Well-watered treatment (ET100%) caused increases amounted to 10.5 & 24.2 in plant height, 21.5 & 34.3% in stem diameter, 10.0 & 21.2% in leaves number plant−1 as well as 60.7 & 114.5% in LAI compared to irrigation with ET85% and ET70%, respectively.
10. The increments in plant height, stem diameter, leaves No plant−1 and LAI due to spraying of AsA than without spraying amounted to 5.2, 10.9, 6.4 and 19.8%, respectively.
11. Sowing sunflower in May and irrigating with 100% produced the highest values of plant height, stem diameter, leaves number plant−1 and LAI exceeding other combinations.
12. All studied growth traits of sunflower showed the highest values with the interaction of 21-May sowing date x AsA(+).
13. Irrigating sunflower plants with 100% of irrigation requirement and spraying with AsA was the potent treatment for promoting plant growth recording the highest values of plant height, stem diameter, leaves No plant−1 and LAI.
14. The distinctive practice in enhancing growth traits was sowing sunflower in May 21 x supplying plants with ET100% x AsA spraying.
III. Yield, yield attributes and WUE
15. The reults revealed that yield, its attributes and water use effeicincy (WUE) were significantly decreased as sowing date was earlier or delayed than the mediate sowing date (May 21) ,except head diameter for earlier sowing date was not significant compared as mediate sowing date.
16. Data demonstrated also that increasing the amount of irrigation levels up to 100% of water requirment enhanced head diameter, head weight, seed weight head-1, seed index, seed yield fed-1, oil yield fed-1 and WUE of sunflower.
17. Plants grown in untreated plots with AsA exhibited the lowest values for head diameter, head weight, seed weight head-1, seed index, seed yield fed-1, oil yield fed-1 and WUE.
18. The data clearly indicated increases in head diameter, head weight, seed weight head-1, seed index, seed yield fed-1, oil yield fed-1 and WUE, obtained by mid-sowing date (May 21) x irrigating by 100% of water requirement.
19. Available results emphasized that the highest values for all yield and its attributes and WUE were achieved from sowing date at 21st May in conjunction with spraying AsA.
20. Irrigating sunflower with ET100% and foliar spraying of AsA produced the highest average of head diameter, head weight, seed weight head-1, seed index, seed yield fed-1, oil yield fed-1 and WUE.
21. The maximum values of head diameter, head weight, seed weight head-1, seed index, seed yield fed-1, oil yield fed-1 and WUE are resulted from sowing sunflower on 21st May in conjunction with both well-watered treatment (ET100%) x AsA(+).
IV. Chemical traits
22. Data indicated that mid-sowing date (21st May) treatment achieved the highest values oil percentage and iodine value (33.82% and 125.38, respectively). 23. The results showed that irrigation at 100% of water requirement (ET100%) induced the highest oil% (36.05%) and iodine value (128.94).
24. Spraying sunflower plants with ascorbic acid resulted in increment in both oil% and iodine value of seeds, amounting to 2.49% and 1.28%, respectively, than seeds of the untreated plants.
25. Sowing date of 21st May x irrigation with ET100% was the efficient practice for achieving the maximum values of oil% and iodine value surpassing other combinations.
26. The superior combination (surpassing other ones) being recoeded the highest oil% and iodine value (34.28% and 126.24, respectively) is through the sowing sunflower by 21st May with foliar application of ascorbic acid.
27. Sunflower plants irrigated by 100% of water requirment (ET100%) either sprayed or not with ascorbic acid recorded the highest oil percentage and iodine values.
28. Sowing sunflower delaying (in 21st June) or earlier (in 21st April) each in combination with 70% of water requirment without spraying ascorbic acid recorded the lowest values of oil% and iodine.