Presidency College, Calcutta
The clay membrane electrode technique of Marshall and others has been employed for measuring the total ionic activities of some Indian soils. The soil suspension in distilled water is connected through the clay membrane electrode with a synthetic soil solution and the potential difference between the two systems measured by inserting a calomel electrode in each side. The soil side becomes positive in such measurements and a lower e. m. f. (obtained in millivolts) corresponds to a higher ionic activity in the soil suspension. These activities have been suggested to represent the immediately available category of plant nutrients present in soils.
A thermodynamic background of the process of nutrient uptake of plants has also been presented.
