Pot experiments were carried out using sand (collected from Ismailia ARS), in the greenhouse to study the effect of biochar application, on K and P release from their natural bearing minerals i.e.,K- feldspar and rock phosphate and\or bentonite on some growth of maize plants parameters, their P and k uptake and the soil available P and K. sixty three pots ever filled with sand(10 kg each biochar was added to all pots expect control at rates 0,1.5 , 3 ton per fed. The studied mineral are K feldspar and rock phosphate as source of K and P respectively. Bentonite was also studied because it is the most common mineral used for reclamation of sandy soil .Each mineral was added at rate of 0,1.5, 3 ton / fed the pots are as follow : biochar alone , biochar + K feldspar and biochar +bentonite and biochar and rock phosphate . maize was planted as the common way in which maize seed 6 grains for each pot inoculated with P and K solubilizing bacteria were planted . the usual N fertilizer (NH4 )2SO4 200kg /fed and irrigated as needed . Maize grow parameter i.e plant height and dry weight of maize plant were measured after 2 months of plantation . K and P as well as their uptake were measure. Results revealed that, the use of biochar at 3 tons fed-1 in combination with 3 tons of any of feldspar, bentonite or rock phosphate enhanced significantly growth parameters of maize plants compared to the control treatments .The highest values plant length and dry matter were were 89.00 cm, 11.4 g pot-1 against 36.6 cm and 2.8 g pot-1 for the control treatments., same treatments increased significantly P and K uptake of maize plants and the soil available p and K compared to the control treatments. The highest significant values in P uptake were 22.5, 18.3 & 16.7 mg plant-1 for the treatments (3 tons fed-1)of biochar with either 3ton rock phosphate ,3ton bentonite or 3 ton K-feldspar .while K uptake were 63.9, 61.8 & 60.1 mg plant -1 for biochar ( 3 tons fed-1 )with bentonite (3 tons fed-1 ), feldspar (3 tons fed-1 ) and bentonite (1.5 tons fed-1 ). Regarding available P the highest obtained values were 49.3 mg Kg -1 for 3 ton biochar + 3ton rock phosphate , 24.1 mg Kg -1 for 3 ton biochar + 1.5 ton bentonite and 24.0 mg/ kg-1 for 3 ton biochar + 1.5 ton K- feldspar. Increase either K- feldspar or bentonite to 3 ton had negative effect on available p .

The aim of this work was to conduct pot experiment to study the ability of plant roots on solubilizing various sources of phosphorus and factors that may facilitate or inhibit their activity. A split medium – split root technique experiment was conducted to study the effect of CaCO3, pH, organic matter (humic acid) and bentonite on the pH, P solubility in the medium and P concentration in bean plants (Vicia faba var. balady). The changes in pH of the lower solution was recorded, also the root exudate was collected in 500 ml of CaCl2 solution 0.5 × 10-4 M and pH 6.85.  Results showed that the highest recorded total dry weight was found when both N forms were applied in the ratio of 1:4 NO-3: NH+4 or NO-3 alone. The mechanism of solubilizing rock phosphate by exudating protons or organic, amino and other organic compounds is possible at the root surface even in alkaline soil as long as the rock phosphate material was added near the root and organic matter was added to limit the fixing power of the inorganic components as CaCO3 and excess soluble Ca. Also, the availability of P from rock phosphate sources depends on its reactivity value.