SOIL ACIDITY TESTS IN RELATION TO SOIL CLASSIFICATION.

By 3. D. Conner, Purdue University Experiment Station.

It is fairly well agreed that one of the most important functionsof a soil survey, is to classify the soils so that farmers may know howto treat them.

No one chemical test that may be made on the soil is c.s importantas a lime requirement test, generally termed "acidity test." There areat least three distinct ways of testing for soil acidity.

First, the measurement of the intensity of the acidity as shown bythe hydrogen ion concentration.

Second, the measurement of the amount of lime a given quantity ofsoil will need to become neutral.

Third, the measurement of the most profitable mount of lime neededto grow particular crops.

Quite often all three types of tests will show accordant results.In some cases, however, they will not. It would seem that investigationsof such differences should fall in the province of the research workersrather than in that of the field men of the soil survey. The field men,however, are in a position to gather much valuable data to help in thesolution of such problems.

An equipment for a soil acidity test for field men should te ina compact portable form. It should be one that would quickly show resultsin a distinct and positive manner on all types of soil, both high and lowin organic matter and on wet as well as dry soils.

The considerable interest and activity shown by different soil surveyparties during the past season in making acidity tests, has no doubt beenfruitful in adding to our knowledge. The purpose of this symposium is tobring together the different experiences .̂nd conclusions of the variousmen who have been working on this problem.

It is to be hoped that practical methods may be worked out that willbe of great aid in improving soil survey classification.

- 56 -