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Volume 62, 1931-32
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Chemical Determinations of Lime Requirements and their Correlation with Field Response.

By J. K. Dixon, John Edmond Research Fellow of the University of Otago.

[Communicated to the Otago Institute by Professor J. K. H. Inglis, 17th June, 1930; received by Editor, 14th July, 1930; issued separately, 30th September, 1931.]

Introduction.

In New Zealand, a new country with so much land as yet undeveloped, it is essential that the proper and economical use of fertilisers should be understood. Field experiments with the use of different manures do give the necessary information eventually, but a “hit or miss” method with so many negative results is unscientific, and means in many cases loss of time and money, especially where the results obtained are applicable to only small areas of country. On the other hand, a chemical investigation of the soil, besides determining the problem, should define more readily the area to which it can be applied.

Unfortunately, chemical analyses have very often not given reliable results, and because of this have fallen into bad repute with agriculturalists. Especially has this been so with the liming problem where chemical predictions as to lime response have often been at variance with the field results. Both the agricultural and chemical methods of determining lime response have certain inherent weaknesses. On the agricultural side, tests are made by observation and by hay weights, and the following faults may be noted:—

1.

The observation method is liable to a 20% error.
2.

Low growing clovers are not cut by the mowers.
3.

The Officers of the Agricultural Department have so wide a field to cover that the plots are often not seen at their best time.
4.

The types of grasses, etc., are not the same on all plots; and on the same land a red clover response would be more readily measured than one of white clover.
5.

The mowing method takes no account of the increase in quality of a pasture.
6.

A limiting factor other than lime would prevent a lime response.

On the other hand the chemical evidence is complicated by the hurrying-up process of the laboratory, which seeks to bring about in a few hours changes which would take a year or more in the field; the reagents used are often unnatural ones, and the results obtained are dependent on time of experiment and ratio of soil to solution. It will thus be seen that since lime forms the basis of the most

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manurial programmes, a thorough investigation into the connection between chemical tests and field response is necessary. With this object in view some of the best lime-requirement methods have been tested against one another on different soil types where the response to lime had been ascertained by field experiments. In this connection the pH of these soils was measured in the hope that should a correlation exist between lime requirements, pH, and field response, an easy colorimetric method for determining the lime needed would be available for use by the farmers themselves.

Experimental.

The methods of measuring lime in status of the soil can be divided into three classes:—

I. Measurement of lime absorption by the soil:

In these methods a dilute solution of lime in a soluble form is shaken up with a weighed quantity of soil. From the amount absorbed the lime requirement is calculated.

II. Measurement of the available lime in the soil:

These methods aim at determining the amount of lime that can be extracted from the soil by certain reagents. This amount is taken as a measure of lime available for the plant. Apart from the “citric soluble” lime method there is also the replaceable base method wherein the lime is brought into solution by base exchange.

III. Indirect Methods:

These depend upon the changes brought about by the varying lime status of the soils, and do not give a direct measure of lime needed or present, but have to be standardised against the direct methods, pH determinations, active acidity, and the measurement of soluble iron in the Comber test are examples of this type.

Methods.

I. Measurement of lime requirement:

(a) Hutchinson-McLennan (1915). 15 gm. soil, 250 c.c. of.02 N Calcium bicarbonate, 3 hours' shaking.

As the apparent lime requirement varies with the residual amount of bicarbonate, a correction is made by the method of Crowther and Martin (1925), and the lime requirement is obtained at constant dilution (.015 N.).

(b) Hardy and Lewis (1929). 10 gm. soil, 40 c.c. of.2 M calcium chloride. Liquor titrated with.03 N lime water to pH = 7.

II. Replaceable Lime: (Hissink 1923).

Smith's adaptation (1925). --25 gm. soil, leached to 500 c.c. with Normal ammonium chloride. Lime precipitated as oxalate and estimated volumetrically by potassium permanganate.

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III. Indirect Methods:

(a) pH Electrometric.

10 gm. soil, 20 c.c. distilled water, sufficient quinhydrone. One minute's shaking and pH determined in usual way, using platinum and gold electrodes.

(b) pH Colorimetric.

10 gm. soil, 20 c.c. distilled water, stirred for one minute and filtered. To half a test-tube of filtrate four drops of B.D.H. Universal Indicator were added and pH judged.

(c) Replaceable Hydrogen (Joffe and McLean, 1926).

10 gm. soil leached to three litres with N Barium Chloride. pH of resultant liquor determined, and electrometric titration made to pH = 7 with.02 N potassium hydroxide. For comparison the figures obtained here have been recalculated in terms of calcium oxide required.

(d) Comber's test for soluble iron. Carr's modification (1921). 50 gm. soil, 30 c.c. of 4% alcoholic potassium thiocyanate. Titrated with alcoholic hydrochloric acid or potassium hydroxide. For comparison the results have been recalculated as lbs CaCO3/acre.

(e) Truog's test.

10 gm. soil, 5 c.c. of solution of zinc sulphide suspension in calcium chloride solution and 95 c.c. water.

Samples.

All soil samples have been air-dried, broken down with a wooden roller. and sifted through a 3 mm. sieve.

Information based on hay weights or observations has been supplied with most of the samples. Each number indicates a new soil type—(a) unlimed, (b) limed. Unless otherwise stated, the term “lime” means carbonate of lime. The terms used for describing the soil types are general and not exact.

Otago:

I. Kinnard. Taieri Plains, near Maungatua.

Eight-year-old pasture in fair condition. Top dressed—1 ton lime 22/7/27. Harvested 18/1/28. Sampled 21/2/29. Hay weights—Control 40.3; limed 46.6. Good response to lime.

II. Withers. Foothills of Maungatua.

Ten-year-old pasture that had run out, cocksfoot, sweet vernal, and Yorkshire fog being dominant. 1 ton lime 21/7/27. Harvested 19/1/28. Sampled 21/2/29. Good clover response, but hay weights did not show this up. Hay weights—Control 22.6; limed 22.9.

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III. Spencer. Taieri Plain, near Contour Channel at Berwick.

Swamp soil. Seven-year-old pasture that had run out. 1 ton lime 29/8/21. Harvested 20/1/28. Sampled 21/7/29. Lime gave a visible response, but mower could not be set low enough to cut the clovers. Hay weights—Control 37.2; limed 37.9.

IV. Garden soil, University of Dunedin.

V. Silt deposited by the Leith Flood in March, 1929, at Dunedin.

VI. Borrie. Papakaio, North Otago.

“Tarry” soil. Response to lime shown by hay weights.

VII. Green. Patearoa, Central Otago.

Idaburn stony loam (Ferrar). Drained swamp at foot of irrigated downs. Fifteen-year-old pasture that had run out, large proportion of Yorkshire fog, sweet vernal, and white clover. No response to lime. 1 ton lime 10/8/27. Harvested 15/12/29. Sampled 1929. Hay weights—Control 42.9; limed 41.2.

VIII. Cratchley. Kyeburn, Central Otago.

Idaburn stony loam (Ferrar). Old river bed of mica schist gravel now forming a terrace to Kyeburn River. Light loam. Pasture run out to goose grass and gorse. Great response to super, but none to lime. Hay weights—Control 12.6; limed 12.8. 1 ton lime 10/8/29. Harvested 15/12/27. Sampled 1929.

IX. Kearney. Ranfurly, Central Otago.

Naseby stony loam (Ferrar). Practically flat land inclined to heaviness, now under irrigation. Twenty-three-year-old pasture, ryegrass and white clover existing in weak condition. Top dressed 1 ton lime 8/8/27. Sampled 1929. No visible response to lime.

X Reese. Berwick.

Swamp soil similar to III. Response to lime.

XI. Robinson. Maropuna, South Otago.

1 ton lime August, 1927. Sampled 5/8/29. Lime response on pasture.

XII. Tweed. Moneymore, South Otago.

1 ton lime August, 1927. Sampled 5/8/29. No response to lime.

XIII. Waikouaiti.

Response to lime.

XIV. Gore, South Otago.

Potash response, but no information yet re lime.

XV. Repeat Sample on XI.

Sample taken from different parts of the field. Sampled October, 1929.

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Nelson:

XVI. Pakihi lands, West Coast.

Lime and phosphate are limiting factors. Burnt and topdressed in 1928 with two tons slaked lime and ten cwt. basic slag.

XVII. Anderson. Riwaka.

Untreated fine sand, used in peach experiments for last four years. Very well supplied with phosphates. Ideal soil for peaches, raspberries, and tobacco.

XVIII. Fry. Riwaka.

Good pasture on coarse sand loam, derived mainly from hornblende granite wash. This pasture, which is high in phosphates, has not been treated for 40 years.

XIX. Mildura. Alongside Sunrise Valley road.

Moutere Hills type. Markedly deficient in lime and phosphate. Responds wonderfully to lime. Control had super alone. Limed—two tons 1922 and 24 cwt. / acre in March, 1926.

XX. Mildura. Near Sunrise Valley road.

Control 5 cwt. of basic slag in 1922. Limed—2 tons limestone and 5cwt. superphosphate in 1922. Good response to lime.

XXI. Saxton. Stoke.

Limed—1 ton per acre. Good response to lime over Control and super alone. (a) Control; (b) Limed; (c) Super alone; (d) fine lime + super; (e) Coarse lime + super.

Southland:

XXII. Udy. Wyndham.

Heavy soil; (a) good turnip land; (b) excellent pasture.

XXIII. Morton Mains.

Good response to lime. Sheep mortality higher than in surrounding districts.

XXIV. Clark. Tussock Downs.

Good heavy country. Response to lime.

South Canterbury:

XXV. Gillingham. Cave.

Medium clay downs. No observed response to lime. 1 ton lime 13/6/28. Sampled 26/8/29.

XXVI. Cleland. Upper Totara Valley.

Good warm clay downs. Observational plot. Excellent response in red clover due to lime. 1 ton lime 23/8/28. Sampled 27/8/29.

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XXVII. Orbell. Levels.

Medium clay downs. Observational plot. Slight response to lime. 1 ton lime 29/6/28. Sampled 28/8/29.

XXVIII. Talbot. Claremont.

Cold clay downs. Observational plot. Excellent response in red clover. 1 ton lime 22/6/28. Sampled 28/8/29.

XXIX. Paterson. Temuka.

Sandy loam with stiff clay bottom. Results expressed as hay weights. Marked response to lime both in 1927 and 1928. Limed 25cwt. 19/7/27, 20cwt. 2/7/28. Sampled 4/9/29.

XXX. Oakley. Albury.

Medium clay downs. Observational plot. Slight response to lime. 1 ton lime 6/7/28. Sampled 27/7/29.

XXXI. Black. Salisbury.

Cold clay downs. Observational plot. Response to lime. 1 ton lime 20/7/28. Sampled 18/10/29.

XXXII. Kelland. Fairview.

Medium clay downs. Observational plot. Limed 1 ton 20/7/28. Sampled 18/10/29. Improvement due to lime.

XXXIII. Orbell. Rosewill.

Warm clay downs. Definite response to lime. 1 ton lime 3/7/28. Sampled 18/10/29.

XXXIV. Brosnahan. Seadown.

Coastal area. Good loam. Slight improvement due to lime. 1 ton lime 21/6/28. Sampled 18/10/29.

North Canterbury:

XXXV. McMullan. Kaiapoi.

No marked response to lime. Pasture sown with wheat in 1927. 1 ton lime 20/7/28. Sampled 13/9/29.

XXXVI. Morgan Williams. Kaiapoi.

No marked response to lime. Peaty soil overlying fairly heavy silty clay. Old grassland. 1 ton lime 20/7/28. Sampled 13/9/29.

XXXVII. Cross. Oxford.

Very good response to lime. Pasture sown down with oats September, 1927. Natural drainage excessive. Light silty loam over clay and shingle. 1 ton lime 3/8/28. Sampled 17/9/29.

XXXVIII. Skurr. Oxford.

Good response to lime. Down in pasture at least 12 years. Heavy clay loam overlying heavy clay subsoil. 1 ton lime 3/8/28. Sampled 17/9/29.

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Mid-Canterbury:

XXXIX. Morris. Winchmore.

Stony medium plains. Pasture two years old, consisting of ryegrass, cocksfoot, fog, and clovers. Slight response to lime. Limed 1 ton 18/8/28. Sampled 2/8/29.

XL. Bonnington. Riverside.

Stony medium plains. Two-year-old pasture composed of ryegrass, brown top, yarrow, ribgrass, and clovers. Response to lime. Limed 1 ton 18/7/28. Sampled 5/8/29.

XLI. Stewart. Rakaia.

Heavy land on terrace adjoining Rakaia River. Silty formation. Pasture two years old, composed of ryegrass, twitches, fog, and clovers. Response to lime. 1 ton lime 26/7/28. Sampled 30/7/29.

XLII. Bonifant. Wakanui.

Medium land. Two-year-old pasture—twitches, ryegrass, fog, and clovers. Lime response. 1 ton lime 18/7/28. Sampled 5/8/29.

XLIII. Goodwin. Lauriston.

Medium soil. Pasture one year old, composed of ryegrass, goosegrass, twitches, and clover. Strong lime response. 1 ton lime 18/8/28. Sampled 2/8/29.

XLIV. Wilson. Dromore.

Stony plains. Sown down with rape in November, 1928. Showing response 27 days after liming. Pasture brown top, ryegrass, red and white clovers. 1 ton lime 3/7/29. Sampled 30/7/29.

Table.—Column 4 gives the Hutchinson-McLennan lime requirement determined in the ordinary way, while column 5 gives the figure corrected to.015 N. dilution. From the figures in column 5 the amount of CaO present has been calculated (column 6) for comparison with other lime requirement methods and replaceable lime (13). Columns 7 and 8 are derived from the two other methods of determining lime requirement, while column 9 figures are from the Comber test. In columns 10, 11, and 12 the ph figures are compared, and in 14, 15, 16 the ratios from lime requirements and replaceable lime. Column 17 gives a rough measure of the capacity of the soil for lime—the amount of lime available if the soil were fully saturated.

Although not shown in the table the active acidity has been measured by the method of Truog, and the ph determined colorimetrically using B.D.H. Universal Indicator. The results of both these methods followed closely the electrometrically measured ph, and distinguished between soils at intervals of.5 ph.

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Lime Requirement Methods
CaCO3 CaO pH CaO Replac. Ratios Capacity
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
Sample Description Response to Lime Lime Reqm. as found CaCO 3% Lime Reqm. (4) corrected CaCO 3% (5) Recal. as CaO % CaO Reqm. cal. from Replac. H CaO reqd. to titrate to pH = 7 Comber Test. lbs. CaCO 3 per acre pH on aq. extr. pH on Bacl 2 extr. pH on CaCl 2 extr. Replac. Lime CaO % CaO Reqd. (6)
CaO Replac. (13)		 CaO Reqd. (7)
CaO Replac. (13)		 CaO Reqd. (8)
CaO Replac. (13)		 Sum Replac. CaO (13)
CaO Reqd. (6)
I a Yes .37 .36 .20 .14 — 2200 5.8 4.9 — .16 1.3 .9 — .36
b .27 .26 .14 .11 — 1850 6.0 5.1 — .17 .9 .7 — .31
II a Yes .27 .26 .14 .12 — 1900 5.8 4.9 — .16 .9 .8 — .30
b .24 .23 .13 .10 — 1770 5.9 5.1 — .17 .8 .6 — .30
III a Yes .68 .76 .42 .29 — 5460 4.7 4.6 — .28 1.5 1.0 — .69
b .68 .76 .42 .25 — 5050 4.8 4.7 — .31 1.3 .8 — .73
IV .15 .13 .07 .04 — 890 7.2 5.8 — .62 .1 .06 — .70
V .06 .05 .03 .03 — 4070 6.8 5.8 — .49 .06 .06 — .52
VI a Yes .18 .16 .09 .06 — 1010 6.2 5.3 — .55 .2 .1 — .64
b .08 .07 .04 .03 — 260 6.7 6.2 — .46 .09 .07 — .50
VII a No .01 .01 .004 .04 — 90 7.7 5.8 — .29 .01 .1 — .29
b .04 — — — — 20 7.9 — — .28 — — — —
VIII a No .02 .02 .01 .05 — 260 6.8 5.4 — .29 .04 .2 — .30
b .03 .03 .01 .05 — 220 6.6 5.4 — .30 .04 .2 — .31
IX a No — — — .06 — 410 7.0 5.5 — .19 — .3 — .19
b .02 .02 .01 .05 — 410 6.5 5.7 — .18 .05 .3 — .19
X a Yes .66 .72 .41 .29 .49 6970 4.9 4.8 4.3 .24 1.7 1.2 2.0 .65
b .65 .70 .40 .29 — 5940 4.9 4.7 — .26 1.5 1.1 — .65
XI a Yes .07 .06 .04 — .07 — 6.3 — 5.3 .26 .1 — .3 .30
b .12 .11 .06 — .12 — 5.3 — 4.8 .19 .4 — .6 .25
XII a No .07 .06 .03 — .07 — 6.4 — 5.4 .20 .2 — .4 .23
b — — — — .12 — 5.6 — 4.7 .13 — — .9 —
XIII a Yes .24 .23 .13 — .17 — 5.4 — 4.6 .12 1.0 — 1.4 .25
b — — — — .16 — 5.6 — 4.6 .14 — — 1.1 —
XIV a .27 .24 .13 — — — 5.3 — — .16 .8 — — .30
XV a Yes .13 .11 .06 — — — 5.9 — — .22 .3 — — .28
b .13 .11 .06 — — — 5.5 — — .18 .3 — — .24
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XVI a Yes .47 .48 .27 .31 — 5710 4.4 4.2 — 0 — — — .27
b .39 .39 .22 .25 — 3620 5.2 4.7 — .21 1.0 1.2 — .43
XVII No .09 .08 .05 .09 — 1770 6.2 5.1 — .13 .4 .7 — .18
XVIII .35 .34 .19 .20 — 4930 5.5 4.8 — .15 1.2 1.3 — .34
XIX a Yes .31 .30 .17 .24 — 6280 5.2 4.9 — .02 7.0 12.0 — .19
b .17 .15 .09 .14 .12 3650 5.6 5.5 4.5 .09 1.0 1.6 1.3 .17
XX a Yes .18 .17 .10 .13 .16 3480 5.3 4.9 4.4 .03 3.3 4.3 5.3 .12
b .10 .09 .05 .09 .07 1980 6.0 5.0 4.8 .14 .4 .6 .5 .19
XXI a Yes .24 .23 .13 .17 .16 3620 5.8 4.9 4.5 .08 1.5 2.1 2.0 .21
b .20 .19 .12 .13 — 2340 5.9 5.1 — .11 1.4 1.2 — .21
c Yes .23 .22 .10 .16 — 3790 5.7 4.9 — .09 .9 1.8 — .21
d .13 .12 .07 .09 .08 2070 6.2 5.5 5.0 .16 .4 .6 .5 .22
e .19 .17 .10 .13 .14 2620 5.7 5.3 4.7 .13 .7 1.0 1.1 .23
XXII a — — — — .14 — — — 4.9 .21 — — .7 —
b — — — — .16 — — — 4.9 .12 — — 1.3 —
XXIII Yes — — — — .23 — — — 4.5 trace — — — —
XXIV Yes — — — — .20 — — — 4.5 .06 — — 3.3 —
XXV a No .17 .15 .08 — — — 5.8 — — .15 .6 — — .24
XXVI a Yes .24 .22 .12 — — — 5.2 — — .12 1.0 — — .34
b .19 .17 .09 — — — 5.7 — — .16 .5 — — .25
XXVII a Yes .25 .22 .13 — — — 5.3 — — .12 1.1 — — .24
b .22 .20 .11 — — — 6.0 — — .16 .6 — — .27
XXVIII a Yes .29 .26 .15 — — — 5.5 — — .10 1.4 — — .25
XXIX a Yes .32 .29 .17 — — — 5.2 — — .14 1.2 — — .31
b .19 .17 .10 — — — 6.1 — — .27 .4 — — .36
XXX a Yes .48 .46 .26 — — — 4.6 — — .04 6.9 — — .29
b .40 .37 .21 — — — 4.9 — — .13 1.5 — — .34
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XXXI a Yes .21 .18 .10 — — — 5.7 — — .09 1.2 — — .19
XXXII a Yes .25 .23 .13 — — — 6.1 — — .11 1.1 — — .14
XXXIII a Yes .22 .20 .11 — — — 6.1 — — .15 .7 — — .25
XXXIV a Yes .23 .20 .11 — — — 5.8 — — .10 1.1 — — .21
XXXV a No .15 .13 .07 — — — 6.0 — — .24 .3 — — .31
XXXVI a No .36 .33 .19 — — — 5.7 — — .29 .6 — — .47
XXXVII a Yes .44 .42 .24 — — — 4.9 — — .05 4.9 — — .29
XXXVIII a Yes .28 .25 .14 — — — 5.3 — — .11 1.4 — — .25
XXXIX a Yes .27 .25 .14 — — — 5.5 — — .12 1.0 — — .26
XL a Yes .19 .16 .09 — — — 5.8 — — .09 1.1 — — .18
XLI a Yes .16 .14 .08 — — — 5.8 — — .10 .8 — — .18
XLII a Yes .18 .15 .09 — — — 5.6 — — .09 .9 — — .18
XLIII a Yes .24 .21 .12 — — — 5.3 — — .09 1.4 — — .21
XLIV a Yes .22 .19 .11 — — — 5.4 — — .06 1.9 — — .17
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Practically all the soils behaved normally in that the process of liming decreased the lime requirement, and increased the ph and replaceable lime. Three soils, however, showed abnormal features.

1.—VI, where the application of lime had apparently decreased the replaceable lime on the limed plots compared with the Controls.

2.—XI, duplicated by XV, where the application of lime had decreased the replaceable lime and ph, and increased the lime requirement as shown by two different methods. In both these soils (VI, XI, XV) the Agricultural report on the response obtained was at variance with the predictions of all the chemical tests.

3.—XII, where the application had decreased the replaceable lime and ph and increased the lime requirement. The Agricultural report agreed with the predictions of the chemical analyses.

Although the cores collected to make the samples, and the analyses made on them were sufficiently numerous to make the results reliable, in view of the possibility of there being an error in the field work, it was thought advisable to neglect these in drawing general conclusions.

Conclusions.

The general correlations between field response and chemical tests are given below. The soils examined are classified into two groups:—

  • A. Sufficient soils have been examined by the methods of this group to make results reliable.

  • B. A limited number of soils have been examined by the remaining methods and only approximate conclusions can be drawn. The methods used for this examination compared less favour ably with those used in Group A.

  • A. (1) Lime requirement (CaCO3) Hutchinson-McLennan.

  • Response to lime <(.17–.18%)> No response to lime. Two exceptions in 38 soils.

  • (2) Replaceable lime (CaO).

  • No response to lime <.25% < Response to lime. Five exceptions in 40 soils.

  • (3) ph Value (electrometric).

  • No response to lime < (5.8–5.9) < Response to lime. Five exceptions in 38 soils.

  • [The section below cannot be correctly rendered as it contains complex formatting. See the image of the page for a more accurate rendering.]

    (4) Ratio given by CaO required/CaO replaceable. (From Hutchinson-McLennan corrected figure).

  • Response to lime < (.5–.6) < No response to lime. No exceptions in 38 soils.

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  • B. (1) Comber test. Eight soils.

  • Response to lime < (approx. 1000lb CaCO3 /acre).

  • > No response to lime.

  • (2) Lime requirement CaO (Hardy and Lewis). Eight soils.

  • a. Original ph < ph = 5.4. Response to lime.

  • b. Lime requírement (CaO) <.16%. Response to lime.

  • [The section below cannot be correctly rendered as it contains complex formatting. See the image of the page for a more accurate rendering.]

    c. Ratio.CaO required/CaO replaceable.

  • Response to lime < 1.0 < No response to lime.

  • (3) Lime requirement (BaCl2 extract). Fourteen soils.

  • a. Origínal ph.

  • No response to lime> (ph = 5.1) < Response to lime.

  • b. Lime requirement (CaO).

  • Response to lime <.09% < No response to lime.

  • [The section below cannot be correctly rendered as it contains complex formatting. See the image of the page for a more accurate rendering.]

    c. Ratio.CaO required/CaO replaceable.

  • Response to lime <.7 < No response to lime.

General:

1.

Comparison of values given by lime requirements (CaO) from three methods.

A1 : B3B : B2b : = 1 : 1.2 : 1.5.
2.

Between the lime requirement and ph methods there is only a rough correlation.
3.

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The approximate capacity for lime (column 17) indicates to what extent the ratio CaO required/CaO replaceable will change between the limed and unlimed samples. A low figure indicates a big, and a high figure a small change.
4.

No conclusions could be drawn as to the effect of one ton of lime (CaCO3) on the constants obtained for the soil before and after liming, since variable factors such as time, climate, drainage, etc., could not be eliminated.

Summary.

The various methods of attack give general indications of the field response to be expected, but they break down in certain cases. Of the direct lime requirement methods, the Hutchinson-McLennan method combines most satisfactorily accuracy with convenience, and since it measures the immediate lime absorption, it is likely to be more comparable with field conditions than the replaceable hydrogen methods (Hardy-Lewis, etc.) which, no doubt, give the ultimate absorption. The Hardy-Turner method suffers from the defect that the readings obtained are a function of the shaking. On the other hand these methods of electrometric titration to ph = 7 give useful curves showing the buffer action of the soil.

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The work indicates that no single factor determination gives satisfactory evidence of field response. Since the acidity is caused by the hydrogen iron, and since lime can ameliorate its effect by reducing acidity, precipitating toxie iron, alumina (possibly), and manganese, liberating phosphates, flocculating clays and promoting bacterial activity, it is reasonable to suppose that the ratio H+ to Ca++ indicates the soil status with regard to lime. (Compare Hissink l.c.) Saturation value V = 100S/T; Comber, ratio absorbed lime/max. lime requirement. The ratio adopted here CaO required (H. McL.)./CaO replaceable has been compared with field response and a good correlation has been obtained for these normal South Island soils. Where the old method of interpreting the Hutchinson-McLennan lime requirement figure in terms of.1% = 1 ton CaCO3 /acre failed was in not realising that as the lime requirement was reduced by liming, the replaceable lime was increased, with the consequence that only a portion of that lime requirement had to be satisfied for optimum soil conditions. The ratio method takes full account of this factor. An advantage of this method is that it is practically independent of the moisture and gravel content of the soil since it is derived from two percentages determined at the same time.

The correlation between laboratory methods and field results must remain at the moment qualitative rather than quantitative, since the agricultural evidence on the effect of lime is based on methods that do not give quantitative results. Until more reliable field trials—such as sheep weights—are introduced, a more rigid examination cannot be made of the chemical methods.

My sincere thanks are due to Dr J. K. H. Inglis, in whose Department this work was done, for his interest and help throughout the investigation. I am indebted to Mr T. Rigg, of the Cawthron Institute, for literature and arranging for samples; to Mr A. W. Hudson, of the Plant Research Station, for arranging for the collection of samples; to Messrs Tennent, Hume, Selwood, Wallace, Calder, Bates, A. Y. Montgomery, and K. Montgomery, of the Department of Agriculture; and Mr G. A. Holmes, of the National Mortgage Co., for arranging for or collecting samples, and supplying information concerning them. Without their co-operation this work would not have been possible. Acknowledgments are due to the Department of Scientific and Industrial Research for a grant for travelling expenses.

References.

R. H. Carr, 1921. Jour. Industr. Eng. Chem., vol. 13, p. 931.

N. M. Comber. Introduction to Scientific Study of the Soil, p. 103.

E. M. Crowther and W. S. Martin, 1925. Jour. Agric. Sci., vol. 15, p. 237.

F. Hardy and A. H. Lewis, 1929. Jour. Agric. Sci., vol. 19, p. 17.

D J. Hissink, 1923. Soil Sci., vol. 15, p. 269.

H. B. Hutchinson and K. McLennan, 1915. Jour. Agric. Sci., vol. 7, p. 75.

J. S. Joffe and H. C. McLean, 1926. Soil Sci., vol. 21.

A. M. Smith, 1925. Jour. Agric. Sci., vol. 15, p. 466.

E. Truog, 1921. Bull. Wisconsin Agric. Exp. Station, p. 321.

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