EFFECT OF SOIL AMENDMENTS ON NI, CD AND PB DYNAMIC UNDER PADDY FIELD IRRIGATED WITH LOW WATER QUALITY

* Haytham M. El Sharkawi 1 and Tamer. F. Metwally 2 . 1. The Central Laboratory For Agriculture Climate, Agriculture Research Center, 296 Imbaba, 12411, Giza, Egypt. 2. Rice Research & Training Center, 33717 Sakha, Kafr EL-Sheikh, Field Crops Research Institute, Agricultural Research Center, Egypt. ...................................................................................................................... Manuscript Info Abstract ......................... ........................................................................ Manuscript History

1170 information of the biochar was given in detail by Pan et al. (2011). In brief, rice husk and wood dust were collected and air-dried. Pyrolysis process was performed in a vertical kiln at 400-450 •C, converting 35% of the biomass to biochar with the absence of oxygen. Compost was prepared at the Central Laboratory for Agriculture Climate through mixing both rice straw and husk by caw manure for 120 days up to maturity. Rice straw was chopped up to 2-3 cm before application either for composting or for direct soil application. The basic properties of all soil amendments in this experiment were given in Table 1.  31.1o E). The study area is located at the north pat of Egypt. Due to fresh water shortage in this region, most of the agricultural lands are using drainage water for irrigation. six soil amendments { rice straw (RS), rice straw compost (RSC), rice husk (RH), rice husk compost (RHC), rice husk biochar (RHB) and wood-dust biochar ( WDB)} in addition to control. The amount of soil amendment applied (Chun et al., 2004;Yuan et al., 2011) was calculated based on the plot area (as shown in table 2), and the amendments were incorporated into a 20 cm depth of soil. All plots were irrigated from Drainage Canal Eight located at Sakha Research station, Kafr El Shiekh, the canal water usually derived from both industrial and Sewage water as characterized in table 3.
Rice cultivar Giza 178 (Oryza sativa )was cultivated under the six treatments as mentioned above. The treatments were arranged in to strip plot design with four replications. Each plot about 50m 2 area. A basal dose of phosphorus was applied at the rate of 36 Kg P h -1 and zinc was added at the rate of 24 Kg Zn ha -1 as ZnSO 4 in dry soil. Nitrogen fertilizer was split-applied as a Urea at the rate of 150 Kg ha -1 ; 2/3 of N dose was incorporated before flooding and 1/3 was applied at the panicle initiation stage. The rice seeds were sown in the last week of April for the nursery. After 25 days, 4-6 plants per hill were transplanted at a spacing of 20x20 cm. Crop was harvested, in the last week of September, from each treatment within an area of 5 m 2 to determine the yield (ton ha -1 ).
Sampling and chemical analysis:-Soil texture was determined by the pipette method (Soil Survey Laboratory Staff, 1992). Soil organic matter was measured by the modified Walkley and Black method as described by Allison. Total N was measured using Kjeldehl method (Bremner and Mulvaney (1982). Water-soluble phosphorus was determined colorimetrically by a spectrophotometer and the contents of water-soluble Ca, Mg, Na, and K were determined using an atomic absorption spectrophotometer (AAS). The pH was measured in a saturation paste, and the electrical conductivity of the saturation extract ( ECe) was measured using an electrical conductivity meter (Page et al., 1982). The CEC was extracted with 1M NH 4 OAC (buffered at pH 7.0), and exchangeable base concentrations were measured using AAS (Shimatzu). Irrigation water samples were collected through the growing season to determine the chemical analysis as shown in Table 4 Table 3: Chemical analysis of soil and the irrigation water plants from each plot were also sampled. The sampled plants were washed with tap water and deionized water in the order, then separated into straw and grains, oven-dried in an oven at 80 C o to constant weight and the grains were milled into powder for measurement of heavy metal content. Thereafter, the samples were ground into powder form to pass a 1mm-sieve and digested with a mixture of sulfuric acid (H 2 SO 4 ) and hydrogen peroxide (H 2 O 2 ) at 240 to 260 C o for 5 hours. The concentrations of heavy metals (Ni, Cd and Pb) were determined using the AAS. Soil samples also were taken from paddy soil (0-30 cm) for determining available Nickel (Ni), Cadmium (Cd) and Lead (Pb) according to methods given in Handbook by Soltanpour (1985) and Page et al. (1982). The same procedure without samples was used as blank. Three replications were conducted for each sample. Plant metals uptakes were calculated based on biomass and metals contents in plants.
For analysis of available heavy metals in soil, air-dried soils were extracted by a die thylenetriaminepenta acetic acid (DTPA) extract using an AAS. A hundred ml of 0.05m DDTPA per 10 g of soil was shaken for 3 hours at room temperature, and then the solution was filtered (14) (Page et al., 1982). Metal contents in the supernatant liquid were measured with a flame atomic absorption spectrometry (FAAS). The same procedure without samples (blank) was used as control. The bioaccumulation factors were calculated as the ratios of metals concentrations in brown grain to the concentration in 0-20 cm paddy soils (Rezvani and Zaefarian, 2011

*Olsen et al., 1954
1172 Statistical analysis Data were statistically analyzed by ANOVA test and L.S.D using a statistical analysis GenStat program and the soil amendments were compared for heavy metals concentration in straw, grain and soil using the least significant difference (LSD) test at 5% level of significance.

Effects of amendments on soil pH, CEC, Eh
The results of soil analysis of some soil chemical properties after harvest are shown in Table 4. The soil properties increased significantly with the application of soil amendments. There is no significant different between RHB and WDB for soil pH, Eh, and CEC. The increase in soil CEC showed that fairly large amounts of exchangeable cations were introduced by soil amendments application. Also the increase of soil pH under pots amended with RHB or WDB could be due to the higher pH in Biochar itself in addition to slow discharge of NH 4 which was stored in porous of Biochar from fertilizer application during the season. The Lowest soil Eh under pot amendment with RSC, RS may be attributed to the low oxidation condition compared to the other soil amendment under study. A chain of reactions is initiated upon soil flooding leading to reduced (low) soil redox potential (Eh, mV) conditions. These reactions include physical, chemical and biological processes that have significant implications for wetland plants (Gambrell and Patrick,1978;Gambrell et al., 1991). Physical processes include restriction of atmospheric gas diffusion in the soil leading to the depletion of soil oxygen and the accumulation of carbon dioxide due to accumulation of organic matter (Jackson andMiller, 2000, Greenway, 2006). Shortly after flooding, with organic matter application the limited supply of oxygen in soil pore spaces is depleted rapidly by roots, microorganisms, and soil reductants (Ponnamperuma, 1972). This process leads to oxygen depletion and reduction in soil oxidation reduction potential (Eh) followed by a chain of soil chemical changes. The processes that follow include denitrification, reduction of iron, manganese and sulfate, and changing soil pH and Eh (Gambrell et al., 1991). For the soil amendments of RSC, RHC and RS, the soil pH was increased in both seasons. This may be attributed to the release of NH 4 in the process of decomposition of organic matter during the growing season; Therefore, biochar as a soil amendment can improve soil quality by increasing soil Eh, pH, and CEC, under flooding condition. The soil pH and CEC values of different soil amendments followed the order: RHB>WDB>RHC>RH>RSC>RS. Regarding to soil Eh the order; RHB>WDB>RH>RHC>RSC>RS. The concentrations of available Cd, Ni and Pb in the soil decreased consistently with the application of soil amendments ( Table 4), suggesting that these amendments reduced the bioavailability of the three heavy metals under study. Compared with the control, the application of RHB, WDB, RHC and RH significantly lowered the concentrations of available Cd, Ni and Pb in both seasons. However, only slight decreases in the concentrations of available Cd, Ni and Pb in both seasons were observed in the treatments of RS and RSC. In general, the concentrations of available Cd, Ni and Pb in both seasons of different amendments followed the common order: RHB>WDB>RHC>RH>RSC>RS>CO which reversed the order of the soil pH except for RS treatment. It can also be concluded that with the application of soil amendment usually resulted in a significant lower concentration of available Cd, Ni and Pb than with no soil amendment application. Soil available Cd, Ni and Pb in both seasons were significantly affected by the soil pH (Fig.1), and the correlation between them can be described by the following regression equations (Eq. (1) Where, Y represents the concentration of available Cd ,Ni or Pb in soil (mg kg -1 ), X represents the soil pH. Several studies have proved that the soil pH is an important Figure 1:-Correlation between soil pH and the heavy metal under study ( the data is average of two years).
factor controlling the mobility of heavy metals in soils (Wallace et al., 1974;Jackson and Miller, 2000). Besides the soil pH, there are other factors such as CEC and Eh that may also affect the bioavailability of heavy metals particularly under flooding soil condition. The properties of the soil amendments as well as the undergoing cations exchange were related to the decrease in the available Cd ,Ni or Pb in the soil. For example, Biochar can release OH-and consequently able to hydrolyze heavy metals cations ( Cd 2+ , Ni + and Pb 2+ ) to Cd-OH + , Ni-OH or Pb-OH which can be adsorbed tightly by soil or Biochar itself, and can thus decrease the availability of these heavy metals (Prasad, 1995). On the other hand, organic amendments such as RSC and RHC enhance the adsorption of heavy metal by soil through forming stable complexes with heavy metal ions, and then decrease their mobility and extractability (Piccolo, 1996;Naidu et al., 1997;Chen, 2000). In this study, the soil pH and the concentrations of available Cd, Ni or Pb in the soil in the Biochar treatments were all lower than the other soil amendments under study. This may be attributed to the enhanced heavy metal adsorption and sorption owing to the large specific surface areas, rich with fiber carboxyl acids groups, and strong ion exchange capacity in Biochar treatment (Wang et al., 2007).
In general, the mobility and availability of heavy metals are controlled by adsorption and desorption characteristics of soils (Krishnamurti et al., 1999 Valdes (2002) indicate that total acidic groups on carbonaceous material can reach at least 2 meq g -1 with half the acidic groups being carboxyl groups. The acidic nature of oxidized biochars means that they may be well suited for retention of basic ions such as ammonium or other cation compounds (Kastner, 2009).

Effects of soil amendments on Ni, Pb and Cd dynamic:-
Metal uptakes in total and the aboveground plant biomass were calculated and listed in Figure 2. As a result of increased metals concentrations in the aboveground, metals uptakes in rice plant were mostly higher in RS treatment compared with other soil amendments under study. For the uptakes in aboveground organ of rice, uptakes of Cd, Ni and Pb were almost the same under both RHB and WDB in both seasons. From Table 5 also, it can be estimated that the reduction of heavy metal concentrations in straw compared to the control are as follows ; Cd ranged from 16 Table 5:-Concentration of Cd, Ni and Pb in rice straw under different soil amendments lime; they also found that compost and lime decreased the Cd fraction extracted with H2O and Ca(NO3)2 and increased the residual fraction of Cd. Narwal and Singh (1998) also reported that pig manure and peat decreased the concentration of DTPA extractable Cd (available) in soil, but increased Cd in residual fraction. In the present study as shown in Table 6, the concentrations of available Ni, Cd and Pb under the soil amendments decreased by 14.45-55.50 % and 17.39-30.43% for Cd and 8.03-24.08% and 9.94-28.06% for Ni, and 17.71-34.00% and 13.22-25.42% for Pb in both years respectively. Furthermore, soil adsorption capacity also affected the uptake of heavy metals by plants. For example, organic amendments can increase the absorption and immobilization of these metals in soil, and therefore decrease the uptake of these metals by rice (He and Singh, 1993). RS. This may be because either the adsorption more of some available heavy metals on RHB and WDB than other the soil amendments or due to their function group or specific surface area. In addition, the decrease of Ni, Cd and Pb concentrations in grain and straw of rice in the treatments of amendments application may be partially attributed to the dilution effect caused by the significant increase of rice yield. The heavy metals concentration in rice grain under the soil amendments followed the same order: RHB < WDB < RH< RHC < RSC < RS < control. The concentrations of the heavy metals in rice grain were lower than those in straw regardless of the sources of amendments.
Bioaccumulation factors of metals under different soil amendments were listed in Table 8. It indicated that grain accumulated more metals under RSC, RHC and RS and accumulated fewer metals under RHB and WDB. Compared with control, there are high significant different between soil amendments for bioaccumulation in rice grain in both years, although there is no significant different found between RHB and WDB in both years.
Heavy metals in soils affect yield after their uptake and accumulation in tissues. Moreover, the accumulated heavy metals could severely harm human health through the food chain (Sorrell, 1999;. International Agency for Research on Cancer (IARC) has reported that Cd and Pb were believed to be carcinogens for humans (Van Wijck et al., 1992;Laskov, 2006). In the present study,  3). the grain yield of rice under the soil amendments followed the order: RHB > WDB >RHC> RSC > RH > RS > control. these results mean that soil amendments were able to promote grain yield obviously except RS.
It is concluded that the application of amendments induced rice growth, and significantly increased the yield of rice grain. Soil pH was increased and the bioavailability of Ni, Pb and Cd was decreased significantly consistent with amendments application. The availability of Ni, Cd and Pb were significantly affected by the soil pH, and the soil adsorption capacity also affected the bioavailability of the heavy metals under study. The available Ni, Cd and Pb in soil were significantly correlated to the soil pH. Rice husk biochar demonstrated the best efficiency among all the

Soil amendments
1177 amendments in this study; it increased grain yield and decreased the concentrations of Ni, Pb and Cd in rice straw and grain. Application of these amendments also increased the grain yield, yet reduced the heavy metals concentrations in rice straw and grain below the tolerance limits of Ni, Pb and Cd in foods. However, the heavy metals concentrations in rice grain under soil amendments are not exceeded the limit. It is mentioning here the concentration of the studied heavy metals in straw or grain of rice is less the permissible limits as reported by El Sharkawi, et al., 2012. Based on these results, either RHB or WDB could be recommended to remediate the contaminated soil irrigated with low water quality.