الفهرس 
2.1. ORGANIC MATERIALS AFFECTING PLANTOnly 14 pages are availabe for public view
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Abstract
Heavy metals pollution of soil causes many environmental and human health problems. Recent reports have drawn the attention to the importance
of organic matter as an outstanding natural and safe means controlling such
metals behavior in soils. These elements bound on insoluble humic
substances are relatively immobile. Humic carboxylic-COOH, phenolic-OH
and other oxygenic functional (reactive) groups are mainly involved in the
formation of metal-humic (organo–mineral ) complexes and thus reducing the
intensity of soil pollution. Consideration, therefore, has been directed towards
using organic materials and their metabolites, resulted via microbial
decomposition, for controlling the activity of heavy metals in the affected soils,
in a process known as ”Bioremediation”. Therefore, the present investigation has been carried out, in pot
experiments, to evaluate bioremediation of a chemically polluted soil with a
number of heavy metals. and its reflection on plant growth. Samples of an alluvial clay soil were collected from the surface layer
(0-30 cm) of the Experimental Farm, Fac. of Agric., Minufiya University, and
packed in plastic pots. The soil was intentionally polluted with a mixture of
heavy metals, i.e. Zn+ Pb+ Cu, each in the form of acetate, at two collective
levels, referring to their permissible safe levels, i.e. the permissible (120, 70 &
50 mg kg-1 soil, respectively) and their duplicate. Organic materials, namely
compost, biogas manure and humic acid, were added at rates of 5 & 10 g
organic carbon per kilogram soil. Also, the interaction between the organic
additives and the heavy metals introduced to the soil, has been studied to
determine its reflection on plant growth and pollution control. Faba bean ”Vicia faba” and maize ”Zea mays” crops were chosen as test
plants. Faba bean growing plants were uprooted at the two periods i.e. 45
and 90 days after planting, as well as those for maize took place at 30 and 60 days. Plant height, dry weight and nutrient (NPK) and heavy metal (Zn, Pb
& Cu) contents of both crops(and nodule numbers of faba bean roots), as well
as dehydrogenase activity in the polluted soil were determined at each
sampling time. Contents of the assigned heavy metals remained in the soil
were assessed at the end of the experimental duration. The standard
recommended cultivation practices, including chemical fertilization, the
specific diazotroph (Rhizobium leguminosarum) inoculation of faba bean
seeds and irrigation.. etc., had been performed in the present study. The obtained results could be summarized as follows:
1- Application of each of the organic materials (compost, biogas manure or
humic acid) to the natural soil (un-polluted), considerably increased the
faba bean and maize plant height, dry weight, nutrient contents, root
nodules (of faba bean) and dehydrogenase activity in soil, as compared
with the artificially polluted soil, at both periods of plant growth. Such
results improved with increasing the applied dose of the organic
amendments. 3- addition of the heavy metals blend (Zn+ Pb+ Cu) to the natural soil, at their
lower level (the upper permissible safe limit), in absence of organic
supplements, caused a little decrease in the experimental measures, at
both sampling times. 4- At the higher level of the pollutants( double permissible) added to the
organics un-amended soil, corresponding decreases certainly occurred in
the dry weights of the plants, as well as in the macronutrients (NPK) and
heavy metals (Zn, Pb and Cu ) concentrations in shoot tissues and their uptake, numbers of faba bean root nodules and soil dehydrogenase
activity. Data revealed that maize plants were negatively more affected by
soil pollution, at the two growth periods especially at the higher level of
heavy metals composite ,than the faba bean plants. 5- As a result of organic materials application to the soil polluted with such
heavy metals, the harmful effects upon plant height, dry weight, nutrients
absorption, root nodulation and soil dehydrogenase activity had been
reduced, seriously at the higher level. However, values of the experimental
measures generally improved at the lower pollution level. Efficiency order
of the used organic substances on limiting the hazardous action of the
heavy metals could be ranked as follows: humic acid > biogas manure >
compost > organic un-treated soil, at the first plant sampling, but compost
exchanged place with humic acid lately. 6- Increasing the dose of organic amendments from 5g to 10g O.C kg-1 soil
to the heavy metals treated soil had resulted in a more effective alleviation
of the adverse effect of soil pollution and consequently leading to a better
plant growth. 7- Absorption capacity for the determined nutrients showed that, phosphorus in faba bean and potassium in maize, exhibited higher positive responses to the bioremediation process. 8- Analysis of the soil at termination of the experiments, confirmed the positive
effect of the applied organic supplements on diminishing the bioavailability of the introduced polluting elements in the subjected soil and thus lowering
the contents of such composing elements in the growing plants. Compost
was the most efficient in capturing such metals in soil, at this phase, in an opposite reflection on their mobility.