The present work was carried out during two winter seasons 2013/14 and 2014/2015 in order to investigate the effect of potassium fertilizer (0, 36 and 72 kg/feddan, one feddan=0.42ha) and different irrigation levels (irrigation after depletion of 40% from field capacity (Normal irrigation or well water), 60% from field capacity (Moderate irrigation) and 80% from field capacity (Severe water stress) on growth, productivity, quality and some physiological parameters of sugar beet plants. The results indicated that the highest number of leaves, top fresh weight and top dry weight were obtained by applying well water in combination with high K rate, while the lowest was produced with plants subjected under severe water stress in combination with untreated potassium. However, the plants exposed to severe drought stress associated with potassium rates produced higher values of osmotic pressure and proline contents than that obtained by other treatments received moderate or well water associated with the same potassium rates at all growth stages. Applications of normal irrigation x high potassium rate produced highest total carbohydrates at 105 DAP. The present results indicated also, irrigation plants with normal irrigation resulted in the highest root and top yields, while the plants exposed to severe drought stress with unfertilized plants produced the least root and top yields. The same trends were noticed with gross, white and losses sugar yields. Applied of all irrigation treatments in combination with high rate of potassium resulted in an increase in sucrose %, however applied of 80% FC in combination with 72 kg K/feddan produced the highest sucrose percentage followed with applying 60% FC under the same potassium level. On the other hand, irrigated plants with 40% FC in combination with untreated plants resulted in the lowest sucrose percentage. Also, application of 80% FC in combination with 36 or 72kg K/feddan produced an increase in purity percentage; while the plants had no potassium fertilizer produced the least purity percentage when irrigated with well water. Concerning, the K content in juice, the results showed a gradually increase by increasing potassium up to high rate under all irrigation treatments, however under the three irrigation treatments the contents of K seem to be the same, which no differences was noticed among them. On contrary, Na and α-amino nitrogen contents were decreased gradually under all irrigation treatments; however the lowest Na and α-amino nitrogen contents were obtained by using normal irrigation in combination with high potassium rate, respectively. The results in also indicated that TSS %, white and loss sugar yields were gradually increased by increasing potassium fertilizer up to high rate with all irrigation treatments, where the applied well water with unfertilized treatment showed the least content of these traits. |
