Silicon (Si) is an element, not essential, but is beneficial for some plants. The Freundlich model was used to describe Si adsorption on soil samples incubated with different Si and phosphorus (P) concentrations. Soil incubated samples were: T1 soil had no Si or P (control); T2, T3 and T4 soils contained 50, 100, and 200 mg Si L -1 , respectively.

Two field experiments were carried out at Giza Agriculture Research Station during the two growing seasons of 2010/2011 and 2011/2012. This investigation was aired to study the effect of different levels of irrigation i.e. irrigation at 100, 80 and 60% ETO with the soil conditioner such as compost and humic acid on Egyptian clover variety (Fahl) yield, yield components and crop-water relations. The experimental treatments were arranged in a split plot design with three replicates. The main plots represented three irrigation regimes, whereas the sub-main plots represented the test soil conditioners i.e. compost at a rate of 6 ton/fad and humic acid sprayed as 2% v/v solution three times in 15-day interval starting at sowing. The main results could be summarized as follows:-Irrigation regimes had a significant effect on growth traits, yield and yield components of clover crop and maximum values were obtained with irrigation at 100% ET0 (wet regime). On the contrary, minimum values for the corresponding respective characters were recorded with irrigation at 60% ET0 (dry regime). It could be stated that all growth, yield and yield components traits were significantly increased due to applying the assessed soil conditioners, compared with the control.-Seasonal applied water increased as irrigation rate increased, where the values were 1010, 808 and 606 m 3 fad-1 in 1 st season and 1069, 855 and 641 m 3 fad-1 in 2 nd season, respectively, with 100, 80 and 60% ET0 irrigation regimes. In addition, applied water was slightly increased due to the tested soil conditioners.-Water Utilization Efficiency was enhanced under irrigation at 60% ET0 (dry regime) and both compost and similar trend was exhibited with humic acid application. Results showed that application of the tested soil conditioners increased total NPK content of mono-cut Egyptian clover plants and the soil after harvest as well, comparing with the control.

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A FIELD experiment was conducted in sandy soil in Ismailia Governorate, Egypt, during two successive winter and summer seasons cultivated with lupine and sesame, respectively. The aim of this study was to evaluate the effects of three different water regimes (i.e., 0.8, 1.0, and 1.2 accumulative pan evaporation) and applied different rates (3, 4.5, and 6 ton fed -1 ) of bentonite as mineral soil conditioner on crop productivity of both lupine and sesame crops under drip irrigation system. Total content of mineral nutrients of both tested plants were taken in consideration. Results indicated that, the highest actual evapotranspiration (ETa) was recorded under 1.2 accumulative pan evaporation treatment, for both lupine and sesame cropping system, while the lowest one was recorded under 0.8 accumulative pan evaporation. Also, applied 6.0 ton fed -1 bentonite recorded the lowest values of ETa in both seasons, whereas the highest value was obtained under zero ton fed -1 bentonite for the same respective crops. In addition, under Ismailia condition it could be concluded that pan evaporation and Hargreaves equations are more suitable to use for scheduling irrigation for lupine and sesame crops compared with the other equations. On the other hand, lupine and sesame yields (straw and grain/or seeds) along with total content of macronutrients (N, P and K) increased significantly under the irrigation treatment of 1.2 accumulative pan evaporation in presenc of 6.0 ton fed -1 bentonite mineral soil conditioner as compared to other treatments.

A pot experiment was conducted in clay soil collected from Agricultural Research Center farm, Giza governorate, Egypt. Wheat grains (Triticum aestivum L., Giza 168) were cultivated to study the effect of silicate and phosphate ions as well as their interactions on the growth and nutritional status of the growing plants, beside their availability in the studied soil. Silicon (Si) in the form of sodium meta-silicate penta-hydrate (Na2SiO3.5H2O) was added at a rate of 0, 200, 300 and 400 mg Si kg-1 soil, and phosphorus (P) in the form of calcium super phosphate was given at a rate of 0, 3.5, 7.0, 10.0 and 13.0 mg P kg-1 soil to represent 0, 25, 50, 75 and 100% of the recommended rate of P fertilization by the Egyptian Ministry of Agriculture for wheat cultivation. Also, the experiment included combinations between all these concentrations of Si and P. Obtained results showed that Si and P availability increased in the studied soil with increasing either Si or P concentrations added. This means that P availability in soil as an essential element for plant growth can be improved by addition of Si. Also, Si increased in plant with increasing applied Si concentrations. Interaction between Si and P generally increased all parameters of plant growth; such responses were significant for fresh and dry weights of wheat plants at booting stage. It could be recommended that selecting good P fertilization design, including time and rate of addition, goes along with values of available Si in the soil.