AG 801 85 011 FIELD DOCUMEN I 3
Soil Mapping and Advisory Services Botswana
SOIL TESTING PROCEDURES
FOR SOIL SURVEY
Part 2 Laboratory Procedure Manual
UNITED NATIONS
FOOD & AGRICULTURE
44
ORGANIZATION OF THE
0 DEVELOPMENT
UNITED NATIONS
7431
PROGRAMME
GABORONE, 1988
REPUBLIC CF
BOTSWANA
AG: BOT/85/011 Field Document 3
Soil Mapping and Advisory Services Botswana
SOIL TESTING PROCEDURES FOR SOIL SURVEY
Part 2
:
Laboratory Procedures Manual by
Reinhard Breitbart FAO Expert
Food and Agricultural Organization Of The United Nations United Nations Development Programme
Gaborone, 1988
TABLE OF CONTENIN
SAMPLE RECEPTI()N, GRINDING AND STORAGE
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Preparation of saturated soil paste Saturated paste extract . . . . . . . . ELECTRICAL CONDUCTIVITY Procedure . . . . . . .
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Temperature correction
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SOLUBLE SALTS DETERMINATION
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Procedure . Calculations
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PHOSPHORUS DETERMINATION
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Procedure . Calculations
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OR(;ANIC CARBON DETE1RMINATION
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1 normal, neutral ammonium acetate solution 1 normal, acidified potassium chloride solution 4% boric acid solution . . . . . . . . . . . . . . . . . . . . . . Mixed indicator 50% sodium hydroxide solution . . . . . . . . . Sulfuric or hydrochloric acid 0.01 n . . . . . . . .
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Procedure . Calculations
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Equipment. . Reagents. . .
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CEC-DETERMINATION
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Digestion solution . . . . . . . . Standard solutions . . . . . . . Supertloc 127 Flocculant solution
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Extracting solution for Bray and Kurtz I Extracting solution for Bray and Kurtz II Color reagent A . . . . . . . . . . . . . . . . Color reagent B . . . . . . . . . . . . . . Standard solutions for calibration curve .
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Equipment, reagents and standards .
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SATURATED PASTE EXTRACT .
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EXCHANGEABLE CATIONS DElERMINATION . .
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Preparation of Ca/Mg standard solutions (meq/litre) Preparation of K/Na standard solutions (meq/litre) .
Alternative K/Na standard solution in ppm ..... .
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PARTICLE SIZE DETERMINATION Equipment
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Preparation of Solutions Pretreatment of Samples Procedure .
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Ca/Mg and K/Na with Atomic Absorption Spectrometer . . . . . . Preparation of the Varian AAl275 Atomic Absorption Spectrometer Calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . K/Na determination with 'CORNING 400' flamephotometer . . . . .
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SAMPLE RECEPTION, GRINDIN(; AND STORA ;E
Sample reception:
Incoming samples must always be accompanied by a list of all sample numbers in the lot. Check the samples against this list immediately after arrival. Report any irregularities to the soil chemist. The soil chemist or a senior laboratory technician decide which laboratory numbers are to be assigned to the samples.
Record sample numbers and the respective lab numbers in the sample reception book and enter them into the computer data base.
Sample grinding:
Before grinding most samples first have to be dried.
Spread each sample on a tray, together with the sample bag and sample number card. Place in a wind protected spot until dry. Then till back into bag. Write lab numbers on the sample containers with a permanent marker. Arrange sample bags and sample containers in serial order to avoid any possibility of mixing up samples.
Fill an appropriate amount of soil from the sample bag into the 'llynucruste sample grinder. Alter about 1 minute switch oft Fill the tine earth fraction which has passed into the receiver through the 2 mm sieve at the bottom of the grinder into the sample container and discard the reminder. NOTE: Some samples, especially very clay rich samples, form extremely hard aggregates when dry. These aggregates cannot be grinded successfully with the Dynacrush grinder, they might
even destroy it. Crush the aggregates first with a stone or a hammer before filling into the grinder. Be careful not to crush any stones. It no grinder is available crush the aggregates with u rounded piece of wood on a tlat tray and pass the soil through a 2 mm sieve. Store the samples in the sample store room with incrementing lab numbers.
pH-DETERM1NATION
Reagents:
For pH-1120: For pH-CaC12:
distilled water 0.01tn CaCI, solution ( 0.01m CaC12 =
1.11 g CaC12 per
1
litre or
27.75 g CaCI, per 25 liters. ) Buffer solutions: Use pH 7-, pH 4-, pH 9.2-buffer tablets. Prepare according to instructions on the packet.
Equippient:
Two 25 litre drums for water and CaC12-solution.
One pll-meter with electrode. (Zeiss pH-meter 300 with plastic protected 'Orion' electrode 91-55). Two "AD 1-3 three volume one aliquot" dispensers. Procedure:.
Switch the pll-meter in "stand by" position for warning up. Of each sample weigh two times 20g into 100m1 plastic bottles. (One set of bottles is marked 'pll-H20', the other 'pli-CaC12..)
To the samples in the bottles marked pH-1-120' add 50 ml H20
dist. with the dispenser
connected tu the water drum.
l'o the samples in the bottles marked 'pH-CaCI,' add 50 inl
CaCI,-solution with the other
dispenser.
Close bottles tightly, put on shaker in horizontal position and shake for two hours. After shaking retnove samples from shaker and let stand for one hour. Switch the pH-meter into 'measuring' mode. Place the electrode in the pll 7 buffer solution. Wait for stable reading.
(Less than 30 seconds should be required
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if it
takes much
longer the electrode might
require cleaning.)
Set the meter to 7.00 with the calibration control.
Rinse the electrode with distilled water. Place it in the pH 4 buffer solution (for acid soils), reading with respectively in the pH 9.2 buffer solution (for alkaline soils). Set the meter the slope control. (The slope should be greater than 92% - if not the electrode might require cleaning.)
2
7.
Alter calibration immerse electrode into upper part of sample suspension.
Do not stir the suspension. Wait for a stable reading. A change of 0.01 units in 10 seconds is considered a stable reading. Note the value,rinse the electrode with distilled water from a wash bottle and continue with the next sample. S.
Alter pH4120 measurement also measure electrical conductivity of this extract.
(To decide whether or not preparation of saturated paste extracts for electric conductivit. and/or soluble salts determination is required.)
SATURATED PASTE EXTRAC'T
Reagent:
distilled water
1(juif)ntenit:
24-place
.hanical vacuum extractor cups for extractor.
large beakers (800-1000m1) burctie (1(1(1 ml)
spatuLt
Prsparation of saturated soil paste: Weigh 200 g of soil into beakers
With fly.' burette add few ml of water and mix with spatula. Slowly add more water and mix until soil paste glistens as it reflects light, flows slig,htly when
the container is tipped and the paste slides freely and clean off the spatula (for all soils but the soils with high clay content). 4
tfft'
mìxing allow Hie soil to stand for one hour or more. Then check satura
If Ow past,: stiffens or loses its glistening appearance remix svith water.
Free water should not collect on the surface. If the paste is too wet, add addithrwi if soluble salts are to be determined record total amount of water and soil. Cover beakers with watt], glasses and let stand for an appropriate time.
4
criierizi
Saturated paste extract:
For conductivity determination the extraction can be nade a few minutes after preparing the saturated paste. If the soil contains gypsum the conductivity can increase by 1 or 2 mS/cm upon standing.
Therefore it' gypsum is present allow the saturated paste to stand several hours (4-6 hours) before extracting the solution.
If the solution is to be analyzed for its chemical constituents, the saturated paste should stand for 12 hours or more (over night). Place 9cm fine porous filter paper (i.e Whatman no 42,44 or 50) in extraction cups. Moisten with few drops of water and press it on the bottom of cups.
Hang cups into extractor and connect syringes. Transfer samples into cups. Set extractor to about 1 hour extraction time and start extraction.
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ELECTRICAL CONDUCTIVITY
Procedure:
"Franskr saturated paste extract into small narrow vials. The cell constant of the conductivity elretrode, presently in use is 1.00. If other electrode is used check cell constant usually either engraved on electrode or on the connecting cable.
Switch the range of the Zeiss con 602 conductivity meter on 'cal' and set the display to 1000 with the 'cal' knob (calibration of cell constant). Record the temperature of the solutions.
Switch 'range' into the lowest of the three mS/m positions
(do no use the p.S/m range).
Insert electrode into extract.
NOTE: The two platinum electrodes inside the measuring chamber must be completely immersed in the solution. If the extract is not enough prepare a new saturated paste extract of this sample and combine the two extracts. (this can happen with very clay rich soils). Record the reading and continue with the next sample. If the conductivity is out of the set ) switch to a higher range. range, indicated by display of (1. There are rive range settings 0-2000 micro S/m 0-20.0() mS/m 0-200.0 mS/m 0-2000 mS/m 0-20.00
S/m
As already mentioned above only the three mS/m ranges (2-4) should be used.
II otherwise, it must be clearly indicated in the measuring protocol. Calculations and data storage:
Data are reported in mS/cm. To convert mS/m to rnS/cm divide reading by 100. mS/cm = mS/m/100.
6
Temperature correction:
Use temperature correction table to find correctimt factor Figure 1 page 7 (US. Salinity laboratory staff, 1954).
The correction factor also can be calculated with the formula: corr. factor = 2.581+ (-0.493)*LOG (TENIP).
(Logarithmic regression curve calculated from temperature correction table.)
Soil survey data are calculated and stored with a Hewlett Packard HP 86B Micro computer.
7
Figure
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Temperature correctilin table (US. Salinity Laborator
Staff. 1954)
SOLUBLE SALTS DETERMINATION
Equipment, reagents and standards:
tiaiue equipttietit anti same cheinicals as for exchangeable ations ornbined stock solutions: 200 ineq/1 t'a 50
ineq/I
K
+ +
50 ineq/1
50 ineq/I Na
Prepare diluted stock solutions and standard series in the same vay as
f.
determination, only that
the volumetric flasks are filled up with distilled water and not with ainioni;
atCLli4
111114,'t,
PrOtled re:
l'ipette I nil saturated paste extract in to and shake well tu mix.
0
oil volumetric flask
\ Olt: it absorbance readings of simples are too I,.
up will: dc,ii111.: tt
..1
445
can he
chosen.
The 'I, dilution' then is calculated: Size of volumetric flask
:
nil saturated paste extract
Further procedure is exactly as for exchangeable
Calculations:
If linear regression curve is calculated concentration C of soluble cations in ntc:tsioring sointion is: C =-
a*E+b
a, b = regression coefficients E = Extinction (absorbance reading') If no linear regression curve is calculated concentration C ot° soluble cations in measuring solution is:
E/e Extinction (absorbance reading) e = Extinction coefficient E
e is calculated from standard curve:
e = (El/Cl El, E2, E3, Cl, C2, C3,
E2/C2 + E3/C3 +
En = Absorbance readings of standards CI( = Concentrations of standards = Number uf standards 4)
+ En/Cn)
Concentration I: of soluble salts in soil Imeq/11 K
C
ext rac:
.
Soil ] is:
:11);
2.dilution /
C
Seigio (Million 2
(ItItkiimi
iit': II ,t2ti FOE uscii to/ hut cTrait
s(+il -=
i
1)0.1A ,
110
rctsk)
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PHOSPHORUS DETERMINTION (Bray and Kurtz 18e11,1
`1`wo 25 litre drums for extracting solotim:
\lulti-tunnel rack for 33 funnels ot
,6.aineter.
appywk
Vi'ter paper 1Vhatman 44 or 42, 9 cm
Brinkman eolorimeter PC 600 ooloinneter, preleisthl.$
( niNO 1..
'dip
in' pi-obi'o an othcr
Stoll threngit cet!
N111(1ti: one d1iql1
