الفهرس 
Material and methodsOnly 14 pages are availabe for public view
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Abstract
This study was conducted to investigate the effect of the rhizosphere of corn and soybean plants on the
mineralization of P-nitro phenol ”PNP”, dichlorophenoxyacetic acid ”2,4-D” and glyphosate in
clay loam and silty loam soils. The effect of corn and
soybean root exudates as well as synthetic root
exudates on the mineralization process were also
considered.
A modified model system was used for the
cultivaion of corn and soybean seedlings under
laboratory conditions. PNP,2,4~D and Glyphosate were
applied at a concentration of Ippm in the surface of
the soils used. The mineralization of the three
radiolabeled compounds was determined as the amount of
14COz evolved dur~.ng the m~.nera1~.zat i~on process. Corn
and soybean root exudates as well as synthetic root
exudates were added to the surface of the soils under
14 investigation and CO2 evoloved from the
mineralization of PNP,2,4-D and glyphosate was measured
over time of the experiments.
The obtained results revealed that :-
1. Both corn and soybean plants had a non-significant
effect on PNP mineralization in both clay loam and
silty loam soil.
2. In the soil irrigated with either corn or soybean
root exudates, there was a highly significant
difference in PNP mineralization compared with the
soils irrigated
comparative study.
with nutrient solution as a
3. In soil irrigated with synthetic root exudates,
there was a highly significant difference in PNP
mineralization compared with soil irrigated with
deionized water as a control.
4. from the obtained results, it can be concluded
that, both corn and soybean root exudates as well
as synthetic root exudates may provide PNP degraders with a necessary nutrients to facilitate
its mineralization.
5. In comparing PNP mi.ne raLizat i.on in the presence of
·corn and soybean plants, it was observed that there
was a slightly increase in the extent of PNP
mineralization in the presence of soybean plants
than that in corn plants in the same type of soil. 6. It was also observed that,PNP mineralization in clay loam loam soil.
soil was much better than that in silty
7. mineralization was stimulated in the presence of
corn plant compared with soil without plant in clay
loam soil, Therefore, the presence of the
rhizosphere of corn plant may be considered
-responsible for the increase of 2,4-0
mineralization.
8. When pH of 2,4-D soln. was changed from pH= 4 to
pH=6 , the adjustment of pH did not accelerate the
mineralization process.
9. It was observed that, the presence of soybean plant
did not accelerate the mineralization of 2,4-0 in
-clay loam soil.
10. In silty loam soil, the results showed that, there
was non significant increase in 2,4-0
mineralization in soil cultivated with corn or
soybean plant compared with soil without plant.
11. In soil irrigated with corn or soybean root
exudates, the results showed that, there was a
slight increase in 2,4-0 mineralization but this increase was non significant compared with the
same type of soil irrigated with nutrient soln.
12.The previous trend was observed in soil irrigated
with synthetic root exudates.
13. Data revealed that clay loam soil cultivated with
corn or soybean plant showed a significant increase
in glyphosate minerali zation compared with
uncultivated soil, so, the rhizosphere of corn or
soybean plant may provide a favourable environment
”for stimulating the breakdown of glyphosate.
14. In silty loam soil, the results indicated that,
neither corn nor soybean plant showd a significant
effect on glyphosate mineralization.
15. In soil irrigated with corn or soybean root
exudates, the results showed that irrigation with
natural root exudates failed to gave any
significant effect on glyphosate mineralization. 16. The application
sli9ht increase of synthetic root exudates gave a in glyphosate mineralization compared with soil irrigated with deionized water.