SILICATE ROCK POWDER - EFFECT ON SELECTED CHEMICAL-PROPERTIES OF A RANGE OF SOILS FROM WESTERN-AUSTRALIA AND ON PLANT-GROWTH AS ASSESSED INA GLASSHOUSE EXPERIMENT

Soil samples were collected from 20 locations from the south western p art of Western Australia and incubated at 25 degrees C for 60 days wit hout or with finely ground granite powder at a rate of 20 g kg(-1) soi l, equivalent to about 20 t ha(-1) Electrical conductivity and exchang eable Na, Ca and Mg were not significantly affected by granite applica tion for most soils. Conversely, among the 20 soils studied, nine exhi bited a significant increase in exchangeable K (at p<0.01) due to gran ite application. Six of them showed a consistent increase in soil pH a s measured in a CaCl2 extract, corresponding to less than 0.26 pH unit s. The concomitant increase in exchangeable K due to granite applicati on ranged between 10 and 390%. However, in absolute value it amounted to less than 0.07 cmol K kg(-1) soil, suggesting that a maximum of 59 g kg(-1) of the applied granite dissolved during the course of this in cubation experiment. One of the most granite responsive soils was used for a pot experiment conducted with wheat grown for 88 days in a glas shouse. In this experiment, the soil was either untreated (control) or mixed with either granite or diorite powders at six different rates o f application. The wheat biomass and cation contents in plant tissue w ere not significantly affected by the application of diorite at any ra te of application. Conversely, for the granite-treated soil a signific ant increase in wheat biomass was encountered for rates larger than 2. 5 g kg(-1) soil. Since a significant increase in K content was obtaine d at the same rates of application it was concluded that the positive response of wheat growth to granite application was due to potassium s upplied by granite dissolution. The use of granite powder as a potenti al K fertilizer thus needs further attention even though its efficienc y as compared to a soluble fertilizer would almost certainly be poor.