TESTING FOR LIME.

New Zealand Herald, Volume LXIII, Issue 19218, 6 January 1926, Page 13

TESTING FOR LIME.

SOME SIMPLE METHODS. INDICATIONS OF SOURNESS. Practically every farmer can tell, by observation of the natural herbage of his farm, whether the soil is deficient in lime The occurrence in excess of such plants as sorrel, and of others like bracken and gorsc is generally a sign of lime deficiency. Inability to grow clover and lucerne successfully is another infallible indication of a siniiliar condition. Apart from an actual chemical analysis of the soil, a number of tests have been devised to determine whether the soil contains a sufficiency of lime for agricultural needs. A somewhat rough and ready method is to test the soil by drying a small quantity of it I and adding to it a little dilute hydrochloric acid. Effervescence indicates the I presence of a carbonate, most probably | limestone. In neutral or sour soil no j sucji effervescence takes place. Blue litmus paper (obtainable from tlo chemist) may be used to find out if the. soil is sour. A little of the fjoil should be taken from several places in the area to be examined, and the whole should be thoroughly mixed on a clean surface without handling. A small quantity of this mixture should be placed in a clean cup and stirred into a paste. A piece of blue litmus paper should then be pressed into the paste by means of a piece of stick, leaving about half the paper not in contact with tho soil. After some 15 minutes, the paper should be withdrawn and an examination made of that part which has been in the soil. If the blue color has changed to red, the soil is acid. It is suggested by some chemists that an idea of tho degree of sourness is indicated by the depth of the red colour. Two simple tests for soil sourness have recently been devised by Professor Comber, of tho University of Leeds. Ho suggests using either a solution (5 per cent, to 10 per cent.) of potassium salicylate in water, or a saturated solution of potassium thiocyanate in alcohol. To carry out the test, spadefuls of soils are taken from several places in tho field and thoroughly mixed. This mixture is allowed to dry in the air and a teaspoonful of it is then placed in a small bottle, A small quantity (about a tablespoonful) of either of the a»bove solutions is theu added, and the bottle is shaken vigorously and afterwards allowed to settle. The appearance of a red coloration in the liquid above tho soil is an indication of sourness. Neutral soils and those containing plenty of lime givo brownish and yellow colorations. Professor Comber prefers tho thiocyanate test, which works very well when the soil sourness is due to an excess of mineral acid, while, in such soils, the mineral acid would dispel the color given the salicylate test. For the farmer's own use, however, the salicylate test is generally quite satisfactory. The agricultural colleges in England aro now issuing packets of potassium salicylate to farmers with instructions how to carry out the test. With tho notes given above every farmer should be able to decide whether or not his soil is suffering from lime deficiency.