الفهرس 
INTRODUCTION
Heavy Metals in Soils and Organic WastesOnly 14 pages are availabe for public view
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Abstract
Two pot experiments were carried out in the screen house at the Faculty of Agriculture, South Valley University which different organic wastes (sewage sludge, filter mud cake, compost, filter mud cake-compost mixture and sewage sludge-compost mixture) were added at levels of 5, 15 and 30 ton/fed. to different soil types (clay, calcareous sandy and sandy soils ) to evaluate their effects on some soil chemical properties, release and availability of total nitrogen (N), available phosphorus (P), available potassium (K) and some heavy metals (Cd, Ni, Pb, Cu and Zn) in these soils as well as plant dry matter and the uptake of these nutrients and heavy metals by corn plants followed by wheat plants. In addition, an incubation experiment was conducted in the laboratory for 60 days to evaluate the release rate of these metals and CO2 evolution in these organic wastes amended soils.
A. Addition Effect of Organic Wastes on Some Soil Chemical Properties:
1. After corn harvest
a. Decreases in the soil pH of the studied soils were occurred as a result of applying different types and levels of the investigated organic wastes to different soils due to the organic matter decomposition of these organic wastes. the lowest values of the soil pH were obtained in the case of applying these wastes at the level of 30 ton/fed.
b. Highly significant increases were found in the soil salinity (ECe) as a result of applying different levels of all investigated organic wastes to the studied soils. The highest values of soil salinity were found in the case of applying filter mud cake at the level of 30 ton/fed.
c. The organic matter content (OM) of all studied soils increased with increasing the levels of all investigated organic wastes.
2. After wheat harvest
The residual effects of the investigated organic wastes on the pH, ECe and OM of the studied soils after wheat harvest can be summarized as follow:
a. The soil pH reduction increased in all studied soils due to the residual effect of the organic waste application. The pH values of all organic waste amended soils after wheat harvets were lower than those after corn harvest.
b. Highly significant increases in the soil salinity (ECe) were recorded as a result of applying different levels of all investigated organic wastes to the studied soils. The ECe values of all soils amended with all organic wastes after wheat harvest were higher than those after corn harvest.
c. Significant increases in the soil organic matter content were found after wheat especially in the calcareous sandy and sandy soils amended with sewage sludge at the level of 30 ton/fed.
B. Addition Effects of Organic Wastes on N, P, and K Release
1 . After corn harvest
a. The application of all investigated organic wastes at all levels caused increases in N release in all studied soils. Sewage sludge-compost mixture at the level of 30 ton/fed. was the superior in N release in the clay soil while filter mud cake-compost mixture at the level of 30 ton/fed. was the superior in N release in both calcareous sandy and sandy soils
b. Available phosphorus in all studied soils increased with increasing levels of all organic wastes. Filter mud cake added at the level 30 ton/fed. was the superior organic waste in the release of phosphorus in all studied soils.
c. Highly significant increases of available potassium were recorded in the studied soils as a result of applying all investigated organic wastes and the the highest available potassium values were obtained in the case of applying filter mud cake at the level of 30 ton/fed. to all studied soils.
2. After wheat harvest
a. The highest residual levels of the total N in the clay and the calcareous sandy soils, occurred with filter mud cake-compost mixture amendement at 30 ton/fed. However, in the sandy soil,they were it was with filter mud cake application at the same level.
b. The residual available P in the studied soils significantly increased with increasing the levels of the investigated organic wastes. Filter mud cake at the level of 30 ton/fed was the superior treatment which caused increases in the residual available P that reached 541, 404 and 469% of the control treatment in the clay, calcareous sandy and sandy soils, respectively.
c. All types of organic wastes at different levels gave highly significant increases in the residual available potassium. The highest value of the residual available potassium occurred with filter mud cake at the level of 30 ton/fed. in both clay and calcareous sandy soils, while in the sandy soil, it was with filter mud cake-compost mixture treatment at the level of 30 ton/fed.
C. Plant Dry Matter Yield
1. Corn dry matter yield
a. Applications of all organic wastes at all levels caused significant increases in the dry weight of corn plants grown in the clay, calcareous sandy and sandy soils. Such increases were higher in the plants grown in both clay and sandy soils than those grown in the calcareous sandy soil.
2. Wheat dry matter yield
a. The results of dry weight of wheat plants recorded the same trends as those corn plants. However, the increase in the dry matter yield of wheat plants was higher for the plants grown in the clay and the calcareous sandy soils than those grown in the sandy soil.
D. Addition Effects of Organic Wastes on Uptake of N, P, and K
1. Nitrogen, P and K uptake by corn plant
The uptake values of N, P and K by corn plants grown in the clay, calcareous sandy and sandy soils significantly increased with adding the investigated organic wastes at all levels compared to the control treatment. The uptake values of N, P and K by corn plants showed increases in the studied amended soils in the order of the clay soil > the calcareous sandy soil> the sandy soil.
The highest amounts of N taken up by corn plants in all studied soils were recorded for applying sewage sludge at the level of 30 ton/ fed. while filter mud cake amended soils at the level of 30 ton/ fed. gave the highest amounts of P and K that were taken up by corn plants.
2. Nitrogen, P and K uptake by wheat plants
The amounts of N, P and K taken by wheat plants grown in the studied soils significantly increased with increasing levels of the organic wastes from 5 to 30 ton/fed. compared to the control. The highest amounts of N taken up by wheat plants grown in all soils were recorded for sewage sludge added at the level of 30 ton/fed, while the highest uptakes of P and K by these plants in these soils were found with adding sewage sludge-compost mixture at the level 30 ton/fed.
E. Soil DTPA-Extractable Cd, Ni, Pb, Cu and Zn.
1. After corn harvest
a. The application of 5, 15 and 30 ton/fed. of the investigated organic wastes caused increases in the DTPA-extractable Cd of the studied soils. Sewage sludge applied at the level of 30 ton/fed. recorded the highest level of DTPA-extractable Cd in all studied soils, while the compost at all applied levels showed the lowest ones in all soils.
b. Increases in the DTPA-extractable Ni were found in all studied soils as a result of applying different types and levels of the investigated organic wastes. The addition of 30 ton/fed. of sewage sludge recorded the highest values of DTPA extractable Ni in all studied soils. However, the lowest levels of DTPA-extractable-Ni were obtained from applying the compost at all levels.
c. The DTPA-extractable Pb of all studied soils increased with increasing levels of the investigated organic wastes. Sewage sludge applied at the 30 ton/fed. level was the superior in increasing the DTPA-extractable Pb in all studied soils, while the compost recorded the lowest values of the extractable Pb in all soils.
d. Additions of all types and levels of organic wastes to the studied soils recorded highly significant increases in the DTPA-extractable Cu compared to the control treatment. Sewage sludge added at 30 ton/fed. was the superior organic waste concerning the highest values of extractable Cu.
e. Increases were occurred in the DTPA-extractable Zn in all studied soils as a result of applying different types and levels of the organic wastes, the addition of 30 ton/fed. of sewage sludge recorded the highest values of the DTPA-extractable Zn of 16.373, 14.625 and 14.629 mgkg-1 in the clay, calcareous sandy and sandy soils, respectively.
2. After wheat harvest
a. The highest values of residual DTPA-extractable Cd were recorded in all studied soils amended with 30 ton/fed. of sewage sludge while the lowest ones were found with compost.
b. Highest values of the residual DTPA-extractable Ni of 4.662, 4.334 and 4.338 mgkg-1 of the clay, calcareous sandy and sandy soils, respectively, were occurred with adding sewage sludge at the level of 30 ton/fed. to these soils.
c. The highest values of the residual DTPA-extractable Pb were 2.659, 2.320 and 2.307 mgkg-1 for the clay, calcareous sandy and sandy soils, respectively, and occurred with adding sewage sludge at the level of 30 ton/fed. The compost applied at all levels to these soils showed the lowest values of the extractable Pb.
d. Sewage sludge applied at the level of 30 ton/fed. showed the highest value of the residual DTPA-extractable Cu of 2.563, 2.356 and 2.348 mgkg-1 and the residual DTPA-extractable Zn of 19.453, 15.641 and 15.656 mgkg-1 in the clay, calcareous sandy and sandy soils, respectively. The lowest levels of both extractable Cu and Zn were obtained with the compost applied to all soils at all levels.
F. Uptake of Cd, Ni, Pb, Cu and Zn by Plants
1. Uptake of Cd, Ni, Pb, Cu and Zn by corn plants
a. The highest amounts of Cd taken up by corn plants in each studied soil were recorded when sewage sludge was applied at the level of 30 ton/ fed. They were 1.9, 1.5 and 1.8 μg/pot in the clay, calcareous sandy and sandy soils, respectively, while the lowest ones taken by these plants were for the compost amended soils.
b. The highest values of Ni taken up by corn plants grown in the clay, calcareous sandy and sandy soils were 2.5, 2.0 and 2.3 μg/pot, respectively, and occurred with adding sewage sludge at the level of 30 ton/fed. However, the lowest ones taken by these plants were for the soils amended with the compost.
c. Highest Pb uptake values by corn plants grown in the clay, calcareous sandy and sandy soils of 18.5, 15.0 and 16.8 μg /pot, respectively, were occurred when sewage sludge was added at the 30 ton/fed level. The lowest ones were in the compost amended soils.
d. The uptake of Cu by corn plants grown in the clay, the calcareous sandy and the sandy soils significantly increased with increasing levels of the organic wastes. Highest amounts of Cu uptake by corn plants grown in the these respective soils of 83.6, 61.8 and 70.4 μg/pot were recorded when sewage sludge was applied at 30 ton/fed.
e. Applications of these organic wastes at all levels significantly increased the uptake of Zn by corn plants compared to the control treatment. The highest values of Zn uptake by corn plants were 525.2, 380.9 and 446.9 μg/pot in the clay, calcareous sandy and sandy soils, respectively, amended with 30 to/fed. of sewage sludge.
2. Uptake of Cd, Ni, Pb, Cu and Zn by wheat plants
a. The highest values of Cd uptake by wheat plants occurred with the addition of sewage sludge at 30 ton/fed. in all studied soils. They were 1.622, 0.986 and 1.031 μg/pot in the clay, calcareous sandy and sandy soils, respectively.
b. The addition of 30 ton/fed. of sewage sludge recorded the highest values of Ni uptake by wheat plants grown in all studied soils. These values of Ni were 2.133, 1.275 and 1.102 μg/pot in the clay, calcareous sandy and sandy soils, respectively. The compost applied to these soils showed the lowest values of Ni uptake by wheat plants.
c. Highest values of Pb uptake by wheat plants of 15.741, 10.212 and 9.966 μg/pot in the clay, calcareous sandy and sandy soils, respectively, were recorded with applying sewage sludge at 30 ton/fed. Wheat plants grown in the compost amended soils took up the lowest amounts of Pb.
d. The highest values of Cu uptake by wheat plants grown in the clay, calcareous sandy and sandy soils amended with sewage sludge at 30 ton/fed. were 66.017, 37.163 and 45.235 μg/pot, respectively,and coincided with those of the DTPA-extractable Cu in soils after wheat harvest.
e. The highest uptake values of Zn were found with amending sewage sludge, sewage sludge-compost mixture or filter mud cake to these soils at the level 30 ton/fed. The amounts of Zn uptake by wheat plants showed increases in the order of the clay soil > the sandy soil> the calcareous sandy soil.
G. CO2 Evolution and Heavy Metal Release in the Soils with Time
1. CO2 evolution with time
a. Higher concentrations of the dissolved organic carbon (DOC) were found in the soils treated with sewage sludge at all application levels and increased with increasing the incubation period.
b. The addition of all organic wastes to the studied soils led to significant increases in Corg mineralization compared to the unamended soil.
c. The highest amounts of Corg mineralization in all soils were recorded for sewage sludge at all application levels. However, the lowest cumulative amounts of organic C mineralization in all soils occurred with using the compost at all levels. These results could be due to the high microbial activity that it may attributed to the high concentration of dissolved organic C introduced with sewage sludge.
2. Heavy metal release in the soils with time
a. The cumulative DTPA-extractable Cd, Ni, Pb, Cu and Zn in the clay, calcareous sandy and sandy soils increased with increasing the level of investigated organic wastes from 5 to 30 ton/fed. and with increasing the incubation period from 0 to 60 days due to the organic matter decomposition compared to the control treatment.
b. Sewage sludge was the superior organic waste concerning the highest heavy metal (Cd, Ni, Pb, Cu and Zn) release in all the studied soils at all applied levels and incubation periods. However, the lowest values of heavy metal release were found for the compost at all applied levels and incubation periods.
Generally, it may be concluded that the application of the investigated organic wastes increased the soil organic matter, soil salinity and decreased the soil pH of the studied soils. Also, increases in the dry matter yield, the release of N, P, K and heavy metals (Cd, Ni, Pb, Cu and Zn) in the soils and the uptake of these nutrients and heavy metals by corn and wheat plants were obtained with applying the organic wastes at the levels of 5 to 30 ton/ fed. Effects of the investigated organic wastes on these estimated parameters varied among their types and applied levels. Sewage sludge was the superior organic waste with respect to the highest CO2 evolution and heavy metal (Cd, Ni, Pb, Cu and Zn) release in all amended studied soils at all applied levels and incubation periods. However, the lowest values of heavy metal release were found for the compost at all applied levels and incubation periods. Therefore, more studies are needed to investigate the effect of these organic wastes on the plant growth and uptake of nutrients and heavy metals by these crops and its accumulation in the soil under field conditions.
Therefore, it is recommended that the organic wastes that contain high levels of heavy metals and soluble salts such as sewage sludge and filter mud cake should not be added to the agriculture soils, especially the clay one. These metals and salts are released from these organic wastes during the composition of their organic matter. On the other hand, the compost should be applied to the soils, especially the sandy and calcareous sandy soils to improve their properties and increase their fertility because it contains very low levels of heavy metals and soluble salts.