الفهرس 
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Abstract
This investigation was conducted to study the effect of presence or absence of plant roots as well as the effect of soil texture on the oxidation state of Cr under flooding conditions. Also, the effect of Cr (applied at different rates) on growth and biological yield of rice plant was studied.
Plastic pots were uniformly packed with 10 kg portions of the tested soils (clay soil from Moshtohor and sand soil from Inshas). Rice seeds were planted in pots and thinned to 3 plants per pot after 20 days from seeding). Chromium (VI) in the form of K2Cr2O7 ”potassium dichromate” was applied at doses of 0, 10, 20, 40, 80 and 160 mg Cr kg’ at the time of soil preparation. Samples of soil solution as well as plant growth were collected after 5, 20, 35, 50 and 65 days from Cr addition for determination of Cr.
1- Chromium species in soil solution as affected by chromium addition:
a. Trivalent chromium :
The increase in soluble Cr(III) in soil which was obtained by application of 0, 10, 20, 40, 80 and 160 mg
-1
Cr(VI) kg amounted to 0.006, 0.526, 1.845, 1.978,
-1
2.047 and 2.367 mg Cr L .
The reduction of Cr(VI) to Cr(III) seemed very sharp on the fifth day after Cr addition and continued by prolonging the time. In the clay soil, day 5 seemed optimum to achieve the highest rate of Cr(VI) reduction.b- Hexavalent chromium :
Chromium (VI) in soil solution of the sandy soil increased by increasing the rate of Cr(VI) and thus was
1
significant, at the rates of 80 and 160 mg Cr kg . In
the clay soil, there were no significant differences among the different successive treatments.
2. Applied Cr and dry matter yield of rice shoots :
- Application of chromium at 10 mg Cr/kg soil caused a significant decrease in shoots yield. Yield decreased progressively with increased application of chromium. Mean values of yield were 72.7, 61.7, 56.3, 53.1, 48.6 and 45.2 g/pot with addition of 0, 10, 20, 40, 80 and 160 mg Cr/kg-1, respectively. The magnitude of yield decrease caused by adding 10, 20, 40, 80 and 160 mg Cr/kg-1 were all significant, being 15.1, 22.6, 27.0, 33.1 and 37.8 % , respectively.
- The retarding effect of adding Cr on plant growth occurred in both soils; more so in the sand soil.
At 10 mg Cr/kg the decrease in plant growth was slight particularly during the first 5 days; and with progress of time, the retarding effect was sharp and significant in the sand soil but not in the clay soil.
3. Applied Cr and dry matter yield of rice roots :
- Application of Cr significantly decreased the dry matter yield of roots and the decreases were more progressive with increasing rate of applied Cr. Meanvalues were 38.6, 32.7, 28.4, 25.5, 23.0 and 19.8 g
pot due to application of 0, 10, 20, 40, 80 and 160 gg -1
Cr g , respectively.
Yield decreased drastically upon application of Cr to each of the tested soils even at 10 mg Cr kg-1. In the
clay soil yields were 42.7 35.1, 32.1, 29.2 26.3 and -1
23.9 g pot at 0, 10, 20, 40, 80 and 160 lig g ,
respectively. The corresponding values in the sandy soils were 34.5, 20.3 24.3 21.7, 19.7 and 15.7 g pot , respectively.
The reduction in yield of roots was more pronounced in the sandy soil due to existence of more Cr in soil solution of the sandy soil.
Growth of plant roots increased with the age of plant. In the clay soil yields were 20.5, 28.4, 31.0 36.0 and 42.3 g pot at days 5, 20, 35, 50 and 65 of plant age, respectively.
4. Applied Cr and dry matter yield of rice seeds : Chromium application caused slight decreases in seed yield but the decreases were not significant, except at
20 mg Cr kg reaching a significant reduction of 29 %. In the sand soil, reductions in seeds yield due to adding 10, 20, 40, 80 and 160 mg Cr kg were 1, 52, 60, 67
and 72%, respectively. In the clay soil, the decrease was significant at 10 and 20 mg Cr kg (7 and 18%, respectively).5. Applied Cr and Cr content in rice shoots:
Values progressively increased with increasing the rate of applied Cr particularly in the sandy soil.
In the clay soil, values were 5.4, 12.7, 21.5 31.4 84.8
-1
and 198.8 gg g due to Cr application at the rates of 0,
-1
10, 20, 40, 80 and 160 mg Cr kg , respectively. The
corresponding values of Cr concentration in rice shoots grown in the sandy soil were 8.6, 43.1, 130.8, 402.3,
1
837.1 and 1484.4 jig g , respectively.
Cr contents were decreased with time. In the clay soil, percentages of reduction amounted to 45, 68, 92 and 94% at days 20, 35, 50 and 65, respectively. In the sandy soil, increases occurred at days 20 and 35 (52 % and 71 %, respectively) but decreases occurred at days 50 and 65 (85 % and 89 %, respectively).
6 . Applied Cr and Cr content in rice roots:
Values increased due to increasing rates of applied Cr with means for the 0, 10, 20, 40, 80 and 160 mg Cr kg treatments being 135.4, 271.0, 379.5, 531.7, 828.6 and
-1 1283.2 mg kg , respectively.
Values for plant roots was much higher than Cr for plant shoots, and effect in the sandy soil was more pronounced as compared with the clay soil.
7. Applied Cr and Cr uptake in rice shoots :
- Chromium uptake by rice shoots progressively increased with increases application of Cr. Mean values of Cruptake were 0.44, 1.26, 2.81, 6.79, 13.75 and 23.15 mg
-1 -1 pot with addition of 10, 20, 40, 80 and 160 mg Cr kg ,
respectively. Cr uptake was greater in plants grown on the sandy soil than in the clay soil.
Uptake in shoots as well as roots decreased with increased plant age.
8.Applied Cr and Cr uptake by rice roots:
Uptake in roots grown in the sandy soil were 9.41,
14.32 17.95, 23.61, 33.71 and 35.07 mg pot with
-1
addition of 0, 10, 20, 40, 80 and 160 mg Cr kg . The
corresponding values in the clay soil were 0.95, 1.98,
-1
3.25, 7.38 and 15.04 mg pot , respectively.
9.Applied Cr and Cr content in rice seeds :
Chromium content significantly increased with application of Cr in the sandy soil but not the clay one. The applied Cr rate decreased Cr uptake in the clay soil;
in the sand soil the reverse was true.
10.Total chromium in soil (mg kg-1) as determined by INAA technique.
Total chromium in soils determined by INAA after removal of plant roots sharply increased upon increasing the applied rate of Cr; this was progressive in the clay soil in particular.Total Cr in the clay soil was much higher than in the sand one; probably because of higher surface activity of the clay soil as compared with the sand soil.