THE HYDROGEN-ION CONCENTRATION OP THE SOIL IN RELATION TO FLORA AT SQUIRE VALLEEVUE FARM

The intensive study of the relation of the hydrogen-ion concentration of the soil to plant growth has developed mainly within the last twenty years. Gillespie (7) was the first to use the hydrogen electrode on an extended scale as an indicator of reaction in soils. The use of this method, which is now generally accepted as indicating soil acidity or alkalinity, has been based on the assumption that the only direct explanation of soil acidity is the presence of the hydrogen-ion. Much of the work on soil reaction has been carried out in cultivated soils. Weir (17) presents a table on soil reaction in relation to growth of economic plants. However, there have also been many papers dealing with the acidity and alkalinity of natural soils. Salisbury (13) points out that the hydrogen-ion concentration varies not only with the degree of leaching and organic content but also according to the source of the organi