LEATHER : THE SAMPLING OF SOILS. 883

LXXX1X.-The Sampling of Soils. By JOHN WALTER LEATHER,

VARIOUS methods have been utilised by chemists for taking samples of soils frorri fields, but I do not know of any recorded case where these methods bave been tested in order to determine the difference in composition which would be found between two samples taken by a particular method from the same field.

I n relation to an examination of some soils this year, i t seemed to me desirable that the degree of accuracy of the method of sampling should be determined. Had opportunity offered, i t would have been preferable to test the several methods which are employed, but I have only found time to test one of these.

I have latterly employed the auger for this purpose. It is an extremely simple instrument to use and a large number of borings to any desired depth can be taken from a field in a short time. For this reason, I have considered i t as more likely to provide a true sample of the fine earth than any method in which the sample is taken from one or two spots only. Morever, the surface soil is not disturbed in the same manner as when a hole is dug with a spade, and this is of some importance in the case of experimental plots.

The auger which I employ is an ordinary 1% inch or 2 inch iron auger. It may be screwed into the surface soil to any desired depth, and on withdrawing it, a section of the soil adheres to it i f the latter is not quite dry. If a sample of the subsoil is required, then the section of surface soil must be first removed, and the auger replaced in the hole and screwed into the subsoil.

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884 LEATHER: THE SAMPLING OF SOILS.

The samples which I took to test the method were from plots at three of the Indian Experiment Stations. Two of these are situated near Poona, in what is called ‘( regur ” or “black cotton ” soil ; the third is at Cawnpore, in the Indo-Gangetic Alluvium.

Duplicate samples were taken in each case. About a dozen borings were made for each sample. The soil was sun-dried, and the fine earth, namely, that which passed through a sieve of 2.1 mm. mesh, was subjected to analysis.

The tests applied were the determination of (a) the total nitrogen, (6) the available phosphoric acid, (c) the available potash. Regarding these determinations, the following are the experimental errors which I find in practice :

Total nitrogen ............... *OmO02 per cent, Available phosphoric acid.. . f. 0*0005 ,, Available potash , .. . , . . . . . , . ,,

All the samples were of the surface 9 inches of soil,

& 0.001

All the methods for these determinations are extremely accurate, and especially so is the determination of phosphoric acid by the molybdate method as described by Dyer (Trans., 1894, 65, 140). The table on p. 885 includes the results.

A n examination of these figures shows clearly that the variations between pairs of samples from the same plots are not so great as to render the analyses useless. For example, the Manjri soils clearly contain high proportions of available phosphoric acid, whilst the available potash falls in several to near what is believed to be too little ; the .available phosphoric acid in the Kirkee land is with equal certainty low, and similarly the amounts of these constituents in the Cawnpore soils are undoubtedly fairly high.

At the same time, now that methods of soil examination are being devised which enable quite small quantities of some of the constituents to be determined with accuracy, it becomes of greater importance to be certain that the samples are selected in such a manner that the results of these accurate tests may be undoubted.

They were taken with care, and considering the number of borings which went to form each sample, I hoped that the differences would fall below 10 per cent. of the constituent determined in any one case. The variations in about one-half the tests do actually fall within this limit, but in the other half they amount to more nearly 20 per cent. In the case of the nitrogen and the potash, the experimental error of the analytical methods might account for some material portion of these variations, but this would not be so in the phosphoric acid determina- tions. The differences between the amounts of the available phos-

I am personally somewhat disappointed with these samples.

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LEATHER: THE SAMPLING O F SOILS. 885

Nitrogen.

Black cotton soils : i Manjri, Plot x, a, 104 ..................... . . . l

b, 105 ....................... Manjri, Plot 2, a, 106 ...................... . i

b, 107 ........................ Manjri, Plot 3, a, 108 .................. ......'

b, 109 I Manjri, Plot 4, a;, 110 ........................

6, 111 ...................... Manjri, Plot 5, a, 112 ......................

b, 113 ..................... Kirkee, Plot 10, a, 114 ........................

6, 115 ........................ Kirkee, Plot 8, a, 118 ........................

6, 119 .......................

.......................

Indo-Gangetic alluvium :

Cawnpore, Plot W, 3, a, 134 ............ 6, 135 ........... ~

Cawnpore, Plot W, 11, a;, 136 ........... b, 137 ...........

Cawnpore, Plot M, 3, a, 138 ............ 6, 139 ............ b, 141 ...........

Cawnpore, Plot M, 13, a;, 140 ............

Per cent.

0'040 0.048 0.039 0 -040 0,045 0.048 0.045 0'048 0.060 0.063 0.034 0.049 0'044 0.040

0.043 0-051 0.033 0.027 0'054 0'047 0.031 0'032

Available phosphoric

acid. -~ ~ ~

Per cent,

0'0397 0.0389 0'0262 0.0260 0'0374 0'0318 0-0290 0.0350 0'0672 0.0719 0-0052 0.0064 0-0040 0.0039

0.0277 0.0325 0,0255 0.0119 0.0376 0.0332 0.0153 0'0172

Avail able potash.

Per cent.

0*0070 0-0062 0*0070 0.0054 0.0124 0,0132 0.0077 0.0085 0.0155 0,0194 0*0085 0'0108 0'60.54 0.0039

0.0155 0.0194 0.0132 0.0116 0.0248 0.0233 0.0108 0'0085

phoric acid in Nos. 108 and 109, 110 and 111, 134 and 135, 136 and 137 can only be due to comparatively large variations in the samples.

In the meantime, and since the analyses detailed in this communica- tion were completed, I have had an opportunity of perusing Dr. Dyer's recent paper on the phosphoric acid and potash contents of the Rothamsted wheat-soil (PhX Trans., 1901, 194, B. 235). Reference is made therein to the fact that errors due to sampling occur, but no attempt is made t o gauge them. It occurs to me that some of the analyses of the Broadbalk field supply incidentally a very fair measure of this error.

Supposing that the field was originally quite uniform so far as the proportion of total phosphoric acid was concerned, and that no error occurred in either the sampling or the chemical analysis, it will be clear that the amounts of phosphoric acid found in the 1893 samples should vary by the nett quantities of phosphates added to, or lost from, the several plots during the fifty years. For example, Plot No. 3 has been unmanured, and is known to have lost about 467 lb, P,O, in crops. The 1893 samples showed the soil to contain 2956 Ib . per acre, and thus, apart from errors, the original soil contained 3423

VOL. LXXXI. 3 N

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886 LEATHER: THE SAMPLING OF SOILS.

lb. Plot No. 7 has received 3107 lb. and has lost 1122 lb. P,05; the 1893 sample showed the land to contain 5056 lb. and hence the original soil would have contained 3071 lb.

Among the errors which undoubtedly play a part in lessening the value of any such calculations, that of analysis may certainly be neglected. I have found Hehner’s method extremely accurate. The loss of phosphoric acid from the surface soil by drainage has been fully discussed in the paper alluded to, and shown to have been greater from plots liberally manured with phosphates and other minerals than from the plots which received no phosphates.

AS to the original state of the field, if i t was not uniform it is probable tha t i t varied in some uniform manner, such as a higher pro- portion of phosph.ttes at one side than another. I f this had been so (and excluding errors of sampling), such variations should still be shown by the plots on one side of the field containing generally, and after allowing for their particular treatment, more phosphates than the plots on the other side.

The amounts of phosphoric acid, estimated as above indicated to have been in the soil of the several plots in 1844 (the farm manure plots are excluded as the information regarding the amount of phos- phate supplied is uncertain), are as follows :

My experience coincides with that of Dyer.

Such is not the case.

Plot No. 3 .. Plot No. 4 .. Plot No. 10 A Plot No. 1 0 1

Plot No. 7 ..

Plot No. 1 3 . .

Plot No. 14. I

Plot No. 1 2 ..

Plot No. 1 1 .,

Plot No. 5. .. ,

Unmanured. Unmanured since 1852. Ammonium salts. Ammonium salts. Potassium, sodium,

ammonium salts, phos- I magnesium sulphates,

1 phate. Ammonium salts, phos-

phate, and potassium sul- phate.

Ammonium salts, phos- phate, and magnesium sulphate.

Ammonium salts, phos- phate, and sodium sul- phate.

Lb.

per acre found i n

1893.

p20,

2956 3111 3189 3267

5056

531 5

5289

5211

5107

5678 -

Addi- tions in manure.

- 0 - 506 - a2

- 210

-3107

- 3181

- 3216

- 3189

- 3153

- 3256 -

Losses in

crops.

+ 467 + 528 + 582 + 650

+ 1122

+ 1061

+ 1016

+ 1005

1- 861

f 674

Calcu- lated

original tmount.

3423 3133 3689 3707

3071

3195

3089

3027

2815

3096

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SOME EXCESSIVELY SALINE INDIAN WELL WATERS. 887

Theoretically, these amounts should have been all identical, They differ because of the errors to which allusion has been made. The two which play the most important part would seem to be (a ) loss by drainage, which Dyer has shown is greater from the plots manured with phosphates and minerals than from those such as 10 A and 10 B receiving no phosphates ; ( b ) the method of sampling. On account of (a) we should accordingly expect plots 7, 13, 14, 12, 11, 5, to contain too little phosphate now, and the figures relating to them in the above tabletobe toolow, ascomparedwith theother four plots, and thisisactually the case. Had the method of sampling been faulty to a greater extent than about 1 in 10, there wonld have been no such uniformity as actually occurs in these figures, and it may be assumed that it is a t least as accurate a method as tha t adopted in my experiments. Com- pared, however, with the samples taken of manufactured goods, this error is very great. If two samples of such materials are drawn by different men, it is expected that the error shall not be greater than about 1 in 100.

It seems quite possible to reduce very considerably the present error incidental to soil samples, and I hope to be able to communicate the results of further experiments on the subject a t a future time.

DEHRA DUN, INDIA.

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