الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Heavy metals are a dangerous group of soil pollutants. The contamination by heavy metals causes a serious problem because they cannot be naturally bio-degraded like organic pollutants and they accumulate in different parts of the food chain. Soil pollution by heavy metals has become a critical environmental concern due to its potential adverse ecological effects. Agricultural soil has both direct and indirect influences on public health via food production; it is therefore of great importance to protect this resource and ensure its sustainability. Soil microorganisms play a vital role in maintaining soil productivity. Thus, anything that disrupts these microorganisms and their functions in soil could be expected to affect the long-term soil productivity. Because significant quantities of fixed N2 are contributed to agriculture by symbiotic N2 fixation by leguminous crops, and because this is increasingly important in agricultural production of developing countries resulting from farming practices involving lower-input and sustainability, and because most of the Egyptian soils have low fertility and are heavily fertilized, and because leguminous crops are used for food, feed, and forage, studies of the effect of heavy metal on the growth and development of those crops are needed.
One soil amendment that has received much attention recently is biochar. Biochar is a carbon rich product from burning biomass in the absence of oxygen (pyrolysis), and its potential to improve soil fertility, mitigate climate change, decrease the bioavailability of a range of contaminants, and improve soil water relations has been recognized globally. Biochar application has been assessed for a wide range of soils including sandy and clay. Coupling biochar addition with heavy metals could, therefore, be a successful approach to reducing soil contamination and leaching while sustaining crop productivity. Despite the apparent benefits of biochar towards a variety of soil chemical parameters, the effects of biochar on soil microorganisms have received much less attention. However, biochar has feasible effects on soil bacterial population and metabolic activities and the response of soil microorganisms to soil amendment with biochar may vary depending on soils and agricultural practices.
Only several studies have focused on biochar effects on N2 fixation of leguminous crops, as far as we know, no information is available on the effect of biochar on the nitrogen fixation process within heavy metals addition system. Furthermore, the literature simply does not provide enough information on the effect of biochar and nodulation/nitrogen nutrition of most leguminous crops. Considerations of soil-biochar interactions, including the application of biochar to soil for improved agricultural productivity and food security, should be first priority. In this study, the aims of the present dissertation were to study the effect of selected heavy metals on nodulation and N nutrition of soybean plants, and study the effects of these metals separately or in combination with biochar as a soil amendment on microbial and some enzymes activity.
As an effort in this respect, the present study was planned to study the following points:
1- Examine the effects of biochar as a soil amendment on nitrogen fixation and microbial activity under heavy metals stress (our primary objective of this study).
2- Get information about how biochar affecting the nodulation process and investigate if biochar addition stimulating the nitrogen fixation or not?
3- Study the effect of selected heavy metals in soils amended or not amended with biochar on microorganisms that contribute to soil fertility. This includes the main groups (bacteria - fungi - actinomycetes) and their resistant index to heavy metals.
4- Study the relationship between the biochar soil amendments and enzymes related to nitrogen cycle.
5- Study the effect of the selected heavy metals in soils amended or not amended with biochar in the growth parameters of soybean plants.
The obtained results could be summarized as follows:
Part (1)
1- The microbial population was decreased sharply with the addition of the selected heavy elements in both clay and sandy soils without the addition of biochar while the increase was noticeable when adding biochar as a soil amendment.
2- As a result of the interference between heavy metals and biochar, biochar overcame heavy metals problems and maintained a microbial population of major groups (bacteria - fungi - actinomycetes).
3- The use of biochar also led to a higher percentage of fungi than bacteria, which were taken as a guide for the continuation of the agricultural process in both soils under study.
4- There was an increase in the degree of resistance of the major microbial groups to heavy metals when adding biochar to the soil under study.
Part (2)
1- There was a significant increase as a result of adding biochar in both dry weight, fresh weight and nitrogen absorbed in soybean plants in both types of soil under study.
2- There was no clear increase in the plant height, whether or not biochar was used as a soil amendment.
3- Number of bacterial nodules was increased significantly, especially by using the higher rate of biochar compared to the control, either by adding biochar alone or by mixing it with the selected heavy metals.
4- By adding biochar, it was possible to overcome the inhibition of heavy metals of the enzymatic activity (arginase and urease) under study.