Silica concentration in exudation sap ranged from 400 ppm to 800 ppm and that in guttation sap from 100 ppm to 300 ppm and silica concentration in guttation sap increased with the concentration of silica in culture solution to a certain level (Fig. 1). And silica concentration in exudation and guttation sap was higher in the plant grown with stable manure which contains much silica than in the plant grown with mineral fertilizer or green manure. Both addition of H2S to the solution and heavy application of ammonium sulphate to the soil induced root injury and led to retardation in exudation and guttation, and also to decrease in the amount of silica in these saps (Fig. 2). From these results it is suggested that silica concentration in the exudation and guttation saps has a close relationship with the concentration of available silica in culture media or soil solution. It is also suggested that both the ability for exudation and guttation, and the amount of silica in these saps can be utilized as measures to diagnose the root activity.
Crop Science Society of Japan