Intensive study of an acid soil: a comparison of the different methods for estimating the "lime requirement" and the degree of saturation of soils

Abstract

The chief objects of the investigation were (1) to compare the "lime requirements" of certain acid soils as determined by methods in use in various countries and to compare the effects of adding lime in the laboratory and in the field (2) to compare the results obtained by the various methods which have been proposed for the determination of the saturation value of the soil and (3) to determine the amount of Calcium absorbed in the field, its effect on the other bases of the soil and on the crop yield.

For this purpose 10 plots were laid down, 5 in duplicate, the soils all containing practically the same amount of clay 22 - 25'3, but varying amounts of organic matter 10 - 21f. .. short discussion on the methods of estimating organic matter is given, the method used being that of Robinson's, i.e. reduction of sulphuric acid to sulphur dioxide by the carbon of the organic matter and estimation of the sulphur dioxide evolved. The results agree well with the "loss on ignition" and the method would appear to be very useful in routine work. The total nitrogen was also estimated, but no definite ratio could be established between the carbon and the nitrogen - the ratio carbon to nitrogen varied between 13 and 17 - or between the nitrogen and the organic matter.

The pH of the plots in water solution varied between 4.5 and 5 and between 3.7 and 4.2 in N Kc1 solution, i.e. they were highly acidic.

The various methods used in determining the "lime requirements" were (1)Christensen- Jensen - lime rexuired to give pH 7 found by titration with Ca(OH)2.

The buffer power of the soils calculated according to his method is given. (2) Kappen's - Lime required to remove the "hydrolytic acidity" found by shaking soil with calcium acetate or sodium acetate and titration of filtrate with sodium hydroxide. More acidity was liberated by treatment with calcium than -,vith sodium acetate.

(3) Daikahura's - Lime required to remove "exchange acidity" found by shaking soil with normal potassium chloride and titration of filtrate with standard sodium hydroxide. (Kappen's type3 of acidity : "Ijydrolytic Acidity ", ",,Xchange Acidity ", "Neutral Salt Decomposition ", and "Active Lcidity" and also Page's theory that these are not different types, but are all of one kind differing only in degree are discussed.

The various phenomena can be explained by assuming greater amounts of replaceable hydrogen present in the soil complex as the acidity increases).

Hutchison and McLennan - Lime requirement by determining the amount of calcium absorbed by soil from a solution of calcium bicarbonate. The errors of the method pointed out by various observers are given.

The results show that most lime is required to give pH 7, the hydrolytic acidity method less, Hutchison- McLennan still less, and least of all by exchange acidity method.

It is pointed out that pH 7 is perhaps unnecessarily high for many crops so that amount of lime could be decreased. It was also found that time taken for suspension of soil and calcium hydroxide to reach e,uilibrium was longer than 48 hrs., 96 hours and 120 hours being necessary in some cases. This makes the method too long for routine use. The exchange acidity methods give amounts of lime which are tm low for practical purposes.

The results show that most lime is required to give pH 7, the hydrolytic acidity method less, Hutchison- McLennan still less, and least of all by exchange acidity method.

It is pointed out that pH 7 is perhaps unnecessarily high for many crops so that amount of lime could be decreased. It was also found that time taken for suspension of soil and calcium hydroxide to reach equilibrium was longer than 48 hrs., 96 hours and 120 hours being necessary in some cases. This makes the method too long for routine use. The exchange acidity methods give amounts of lime which are tm low for practical purposes.

The Hutchison-McLennan and Kappen's method give results which appear to be suitable. Kappen's method would be useful in practice as being quicker than Hutchison-McLennan, but the amount of soil used 100 gms. could be decreased and 200 c.cs. solution taken.