KEY WORDSAlkalin soil Ammonium Ammonium nitrate Ammonium sulfate Application method Cotton cultivars Incubation Nitrate Nitrate N loss Phytotoxiceffect Sulfur Urea SUMMARYThe effect of sulfur (S) placement and S rate on the efficiency of urea (U) relative to ammonium sulfate (AS) and ammonium nitrate (AN) for cotton were examined in a pot experiment using sandy clay loam soil (pH 7.9). The results showed that AS and AN application in the absence of S increased the yield than U partly because U-induced damage to plants. The combined application of the N sources with S increased the yields and that, the placement of S in the seed horizon in contact with N was more effective than mixing throughout the soil especially with U. These effects were observed with three cotton cultivars. The addition of S to a maximum of 1.5 g/pot gave further increases in yields or the N content of leaves for U, AS or AN. Using the least squares method, it was found that the presence orS significantly increased the efficiency of U than AS or AN. Incubation of S and the N sources with S in the soil was carried out to understand the growth conditions of cotton fertilized by U in alkalin soil. In the case of U-soil system, the pH increased. NO2-N accumulated and considerable loss of N took place. The pH, NO2-N accumulation and the loss of N decreased with S increments.

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The growth of maize (Zea mays L. cv hybrid 2031) plants were evaluated under water stress induced by decreasing soil moisture from 80% of field capacity as optimal value (control )to 40%, 50%, 60% and 70% of FC treatments, being considered as water stress for maize as affected by Si application at five rates (0. 50. 100, 150 and 200mg Si kg -1 soil). This evaluation was carried out in a pot experiment using calcareous soil in a split plot design. The soil moisture levels were applied to the main plots and the silicon levels were assigned to the sub-plots. The results obtained showed that water stress depressed the growth of shoot, relative water content and chlorophyll index values. Addition of Si up to 200 mg kg -1 soil partially improve the growth of shoot and increase the relative water content, chlorophyll index and proline content. The proline content in the leaves was markedly increased under water stress or with silicon application especially under high water stress conditions. The negative relationship between proline content and shoot dry weight, supporting the view that proline accumulation is a symptom of stress damage. Addition of Si increased Si accumulation in the shoot. Analyses of N, P, K, Cu and Zn showed no accumulation of these elements in the shoot under water stress, and added Si even increased their concentrations under water stress. These results suggest that under water stress conditions, silicon nutrition can improves maize plant growth.

This study describes the chemical speciation of Pb, Cr and Zn in soils of Abis area in Egypt. The studied area is located at the North Western part of the Nile Delta, which represents soils developed from lacustreine deposits at Abis region south of Mariut Lake and covers about 40000 fed. Total 41 top soil samples (0-35 cm) were collected from the area for analysis. The total contents and fractions of Pb, Cr, and Zn were determined, and the mobility factor and potential mobility were calculated. Small amounts of Pb, Cr, and Zn retrieved from the soluble and exchangeable phases, the readily available for biogeochemical cycles in the ecosystem. Low quantities of Pb, Cr and Zn could be available to plants. Zn is present in negligible amounts lower than those of Pb or Cr. The results also indicate that most of the metals have high abundance in residual fraction indicating lithogenic origin and low bioavailability of metals in the studied soil. The values of average mobility factor for Pb, Cr and Zn in the soils of Abis area were 7.31, 6.74 and 0.51%, respectively which is less than 10%. Therefore, these elements are highly stable in soil. The average potential mobility of Pb, Cr and Zn were 15.05%. 34.79% and 8.25% respectively. The Zn had the least average potential mobility (8.25%). The order of average potential mobility of metals soils agrees with the percentage reduction in concentration of residual heavy metal.