The selected feldspar rock for thl~ investigation is well known as orthoclase
sediment at Gebel Rod Ashap. It is estimated that the reserves of this d posit are
about 1.2 mUlion Ion. This deposit is slightly alkaline. low salinity and almost free of
gypsum and carbonates accumulations. The total potassium content Is relatively high
(7.14%). ThIs sediment Includes several members of feldspars. The heavy ",etals (Ni,
Pb) in this st!dlment are very rare. The results indicated that the i~CI'e se of the
concentration of water soluble potassium aiter 1 day is very distinct (from 890 to 1580
ppm). However, continuous increment of solubility, but in lower rate until the 7 1!l day.
Also the exchangeable potassium enhanced fTom 2590.0 ppm to 3600.0 ppm after 7
days. The water,soluble potassium reached the maximum (1080.0 ppm) at 4S'C and
decreased at higher temperatures. While the exchangeable form of potassium has
slight increase until 60~C. Re9arding the influence of pH, II is found that increasing pH
raven the 50Iubilily of potassium and the maximum value (695.0 ppm) was t pH 6.0.
However, the addition of feldspar rock to the soil to obtain the adequate concentration
of water soluble potassium, refer to the rate of 7% resulted in 550.2 ppm 9' soluble
potassium. However, the rate of 5% gave 310.2 ppm of water soluble potaasiurn and
390.0 ppm of eXChangeable which is conSidered as a beneficial concentration for
potassium supply In the soil. According to these results it can be recomme ded that
the feldspar rock can SUbstitute the application of chemical potassium fertilizers, which                 is economically quite expensive.