الفهرس 
ContentsOnly 14 pages are availabe for public view
 |  | from | 69 |  |  |
| | | from | 69 | | |
Abstract
Chromium is a non-essential trace element for plant nutrition but is considered an important contaminant in the environment. It occurs in trace amounts in soils, water, plants, and air, but it accumulates in living tissue by varying ratios from 10 to 1000 relative to the substrate concentration in the environment. As a result, biological interest in chromium is largely confined to its toxic properties.
Two pot experiments were carried out at Soil Salinity Laboratory, Alexandria, Egypt to investigate the influence of irrigation with chromium enriched brackish water on soil Cr, growth of sugar beet plants (Beta vulgaris, maribo magna poly) and tomato plants (Lycopersicon esculentum, supper stren p) Soil samples were collected from Sadat City (140 km south of Alexandria City), washed with tap water, air dried, sieved, and packed in plastic pots (35 id x 40 h). The used soil was sandy in texture (97.71% sand) with pH of 7.5 and EC of 2.26dS/m. A basal application of N, P, K, and chicken manure was added to each pot as recommended to improve the soil properties and to increase the plant nutrients. Seeds of sugar beet and seedling of tomato were planted in the pots in Nov., 1997 and in May, 1999, respectively. The plants were irrigated with different treatments after the appearance of the first two true leaves for sugar beet and after 2 weeks after planting of tomato seedling. Irrigation water treatment comprised 3 levels of EC (0.5, 4, and 8 dS/m) and 5 concentration of chromium (0.0, 5, 10, 20, and 40 ppm) as potassium chromate.
A total of 15 irrigation treatments in each experiment were carried out in a completely randomized block design with four replications.
Sugar beet plants were maintained to maturity and plant samples were taken after 4 and 6 months, while tomato plants were grown for 6 weeks until welting symptoms appeared on the leaves. Therefore, tomato plant samples were taken after 4 and 6 weeks from planting. In both experiments fresh and dry weight of shoots and roots of plant samples were measured and Cr content was determined in soil at two depths (0-20cm and 20-40cm) and in dried plant samples The obtained results were statistically analyzed and the results are summarized below :
1)Effect of irrigation water treatments on Cr in soil.
DTPA-extractable Cr from soil was significantly affected by increasing EC levels in irrigation water for the both depths of soil (0-20 cm) and (20-40 cm) after 4 months. The values of extractable Cr were higher in the deep layer (20-40 cm) than that of the subsurface layer (0-20 cm) indicating the leaching of Cr from the subsurface layer to the deeper one. After 6 months extractable Cr from the subsurface soil was highly affected with the EC of irrigation water, while Cr in the deep layer was not affected.
The results indicated that the amount of Cr extracted from soils in both experiments increased with increasing Cr concentration in irrigation water.
2- Effect of EC of irrigation water on sugar beet plants.
Application of brackish water to sugar beet plants significantly decreased fresh and dry weight of shoots, number of leaves, and leaf area of sugar beet plants after 4 months, while the plant height was not affected. At the same time, root fresh weight and root size were decreased by increasing the EC of irrigation water , while root dry weight and root length, of sugar beet were not affected. This may be due to the relatively tolerant sugar beet to EC of brackish water. On the contrary of that, fresh weight, dry weight, and root size of sugar beet were significantly decreased by increasing the EC of irrigation water at 6 months The reduction in fresh weight of roots after 4 months was more than that observed at harvest time (6 months). At EC 8 dS/m, the reduction in root fresh weight was 11.55 % at harvesting time compared with 19.56% at the age of 4 months. This observation showed that the plants up to maturity, can tolerate high concentrations of salts than they can during their early stage of growth. Root length of sugar beet was not affected by EC levels for the two periods of sampling (after 4 and 6 months).