الفهرس 
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Abstract
The present investigation was carried out during the two successive summer seasons of 2009 and 2010 in newly reclaimed area, at the Environmental Studies and Researches Institute Farm (at Sadat city), Minufiya University, Minufiya Governorate, , Egypt. Four sweet potato cultivars; Minufiya 6, Minufiya 66 (was provided by Potatoes and Vegetative crops Reproduction Department, Horticultural Res. Institute) Beauregard (was provided by The International Potato Center) and Abees (was provided by Sabaheya Horticultural Res. Station) were planted under six environments, which were the combinations of 2 years and 3 levels of potassium sulphate fertilizer (107, 160; and 214 Kg K2SO4/ Fed.); under a drip irrigation system. The experimental layout was arranged in split plots in a randomized complete blocks design (R.C.B.D.), with three replicates. The cultivars were arranged in the main plots; while, potassium fertilizer levels were arranged randomly in the sup main plots. The data were analyzed to investigate the effects of potassium fertilizer on vegetative characters, tuber root, and tuber root quality characteristics, and leaves and roots elements. The genotypic and phenotypic variability for some of the morphological, yield and quality characters were also estimated .In addition, the adaptability and performance’s stability were also measured, as well as, the heritability percentages in broad sense and the correlation coefficients between the various pairs among the studied characters. The obtained results could be summarized in the following points:
1) There were significant and highly significant differences among cultivars, potassium fertilizer levels and for (cultivars x fertilizers) interaction on most of the studied characters.
2) The cultivar Minufiya 6 had the highest values of total yield of tubers/fed., total yield of tubers/plant, number of tubers / plant, average tuber weight, number of marketable tubers / plant weight of marketable tubers / plant and tuber dry matter in first season; while, the cultivar Beauregard had the highest value of root productivity, average root weight and roots number, in the second season of the study.
3) There were insignificant differences between the two cultivars Minufiya 6 and Minufiya 66 in their starch contents in both seasons.
4) The results showed insignificant differences, among the four studied cultivars, in their foliage fresh weight and specific gravity, in the second season.
5) Potassium at 60 kg K /fed. gave the highest values of foliage fresh weight, total yield of tubers and marketable tubers / plant, in the first season. However, the potassium level 80 kg K/fed. gave the highest values of total sugars, starch content, reducing sugars carotene and nitrogen and potassium concentrations in leaves and roots, in both season .
6) The effects of the interaction between cultivars x potassium levels were obvious on most studied vegetative characters, yield and its components in the two seasons of the study.
7) The cultivar Minufiya 6 gave the highest root production; with the application of 60 kg K /fed., in the first season; while, the cultivar Beauregard produced the highest productivity, with the application of 80 kg K /fed., in the second season.
8) The obtained results illustrated that most of the studied quality characters, except root specific gravity, were significantly affected by the interaction cultivars x potassium fertilizer levels.
9) Nitrogen and potassium levels in leaves and roots were also affected by the previous interaction of cultivars x potassium fertilizer levels.
10) Potassium levels showed significant and highly significant effects on most studied characters; with the only exception of tuber root specific gravity traits.
1. The first –order interaction (cultivar x year) effects were found significant, on most of the studied morphological and yield characters.
2. The significant and highly significant effects of the second –order interaction (cultivar x fertilizer x year) were detected on most of the studied characters.
3. The stability analyses showed significant and highly significant differences among the evaluated cultivars for all studied characters, with the exception of average tuber weight/plant and foliage dry weight.
4. The calculated values of the parameter “environment + (cultivar x environment)” was found significant for the characters plant length, total yield of tubers / fed., total yield of tubers / plant, weight of marketable tubers /plant, and total sugars and starch content.
5. The calculated values of the parameters “environment (linear)” were found significant or highly significant for most studied characters, with the only exception of foliage fresh weight.
6. The significant and highly significant values of the parameters “cultivar x environment (linear)” of the characters total yield of tubers / fed total yield of tubers/plant, weight Of marketable tubers /plant, tuber shape index, number of shoots, plant length and foliage dry weight, suggested the presence of significant differences from a linear response among the calculated cultivars across environmental factors.
7. The insignificant calculated pooled deviation for all the studied characters indicated that the linear regression was the major component for differences in stability and not the deviation from the linear function.
8. All evaluated cultivars appeared inadapted for all possible environments, and showed instability across tested environments for most of the studied characters. However, cv. Beauregard reflected relatively a better stability and broader adaptability than the others for shoots number and weight of marketable tubers /plant. Minufiya 66 cv. appeared more stable for foliage fresh weight, total yield of tubers / fed., total yield of tubers/plant, number of tubers /plant, average tuber weight/plant and marketable tuber/plant. Menofya6 and Beauregard cv. showed higher stability than the other two cultivars; for tuber shape index, whereas, Abess cv. reflected a relatively higher stability for total sugars, and, Abess and Beauregard cv. for carotene content.
9. Heritability in t