COLLECTION AND PREPARATION

OF SOIL SAMPLES
COLLECTION AND PREPARATION OF SOIL SAMPLES

• Test data are practically useless if the sample is not representative of the area to
be analyzed

• Variation in slope, colors, texture cropping and management should be taken into
account

• Separate sets of composite samples need to be collected from each of such area
and tested separately

• Large areas should be subdivided into smaller parts of uniform appearance

• The method of soil sampling and the amount of soil to be taken mainly depends on
the purpose of which sample is required and the nature of soil
Purpose for which soil are collected are

• Soil fertility evaluation

• Reclamation of saline soils

• Plantation of crops

• Selection of site for aquaculture

Tools and Materials

• Soil sampling equipments - soil tube, auger, screw type auger, post hole auger,
spade and khurpi

• Sampling of soft and moist soil - the tube auger, spade, Khurpi are satisfactory

• A bucket for collecting and mixing the composite sample

• Clean well labeled bags of size (13x15cm)

Sampling for fertility evaluation

• Divide the field into similar kind according to soil heterogeneity

• Take a composite sample from each area after scraping away surface litter by
inserting auger or sapling tube or spade to a plough randomly are selected
plot/area

• Dig a V shaped hole to a plough depth and cut 1.5cm. thick slice of soil from top to
bottom of the exposed face of the ‘V’shaped hole and place in a clean bucket

• Thoroughly mix the soil samples taken from each plot/area in the buckets
• By quartering reduce the bulk and retain 500g. of the composite sample

• Quartering is done by dividing thoroughly mixed soil into four equal parts and
discard opposite quarters

• Remix the remaining two quarters. Repeat the procedure until about 500g of soil

• Store the soil in a clean, labeled beg after air drying in shade at room temperature
Soil information sheet

The labeled tag should have Name and address of the farmer with other details of the
soil and area
• Village _________,
• P.O___________,
• District __________,
• State___________,
• Field No.__________,
• Depth of sampling______,
• elevation (uplad/lowlad) _____,
• Drainage (good/poor)___________,
• Irrigated or Rainfed_________,
• Sources of irrigation_______,
• soil type (Course weathering water logged, salt affected etc.),
• crop grown__________ etc
Sampling for soil reclamation or site of Aquaculture

• Samples - either using soil auger or drying a 100cm. deep pit

• The soil /samples should be collected as follows:

– Make one side of the pit vertical and collect 500g

– soil sample from marked layer i.e., 15-30, 30-60 60-100cm

– put them separately after drying in shade

Processing and storage of samples

• Soils samples received in the laboratory should be allotted lab numbers

• Should be air dried, and then ground to powder using wooden paste and mortar
and sieved through a 0.5mm. polyethylene sieve

• The samples thus prepared should then be transferred to the soil samples storage
room
Precautions:

• Soil samples should be dried only under shade and not in the bright sun or in an
oven

• All materials used for collection and processing of samples should preferably be
made up of stainless steel, plastic or wood in order to avoid contamination due to
undesirable materials

• During processing of samples efforts should be made to repeatedly crush and the
whole of the soil sample through the polyethylene sieve and contamination
through carryover from one sample to the other should be avoided
DETERMINATION OF SOIL CHARACTERISTICS

• Soil texture

• Water holding capacity of soil

• Soil pH

• Soil conductivity

• Soil organic carbon

• Soil nitrogen, phosphorus

• Lime requirement
SOIL TEXTURE

• Soil - mineral and organic particles of various sizes

• The variation in size of the particles and the proportionate amounts of fine and
course materials - soil texture

MECHANICAL ANALYSES OF SOIL

• The process of determining the amount of individual soil separates below 2.0
mm in diameter (sand, silt and clay) - mechanic of analysis.

METHODS

• Interventional pipette method

• Hydrometer method
PIPETTE METHOD

• Based on the principle of sedimentation of soil particles known as stocks law

(Stocks, 1851)

• Stock law stated that the velocity of a falling particle in a liquid medium is
proportional to the radius square of particles and not of its surface

2 (dp-d) r2
V= ---- g X ----------
9 n

Where V= Velocity of following particle

g = Acceleration due to gravity
dp =Density of particle
d = Density of liquid
n = Viscosity of liquid
r = Radius of particle
International pipette method

Soil fractions can be determined by this method

• Coarse sand : 2.0 - 0.2 mm dia.

• Fine sand : 0.2 - 0.02 mm dia.

• Silt : 0.02 - 0.002 mm dia.

• Clay : Below 0.002 mm dia.

Method

Pretreatment and dispersion of soil:

• Pretreatment of soil - to obtain and maintain maximum dispersion

• Weight out exactly 20 gm of 2.0 mm size soil sample into a conical flask

• To dissolve carbonate (Co32- ) and to remove all exchangeable metal ions, the soil is
treated with dilute HCl (2.0N.HCl)

• After acid treatment the organic matter in soil is oxidized by H2O2

• Sometimes removal of iron and alumina by using sodium dithionate citrate

Separation of sand

• After pretreatment, pour the suspension in to the sieve and wash the sieve into
sediment cylinder with excess water to remove silt and clay

• Transfer the coarse material retained in the sieve is transfered to the weighed
bottle, Dry at 105o c and weigh calculate the percentage of coarse sand weight of
dish -----X.g. weight of the dry dish is 4 gm

Weight of dish + dry coarse sand = 7.8

Weight of coarse sand = (Y-X) g

% of coarse sand pair dry soil = Y-X x 100

20

Note: 20 is weight of the soil sample in gram

SEPARATION OF SILT AND CLAY
Separation of clay
• Shake the contents and pour sample into the sedimentation cylinder

• Allow it for settlement Withdraw 25ml. suspension using volumetric bulb pipette
pour a depth of 10 cm. after ____ lapse g.

• Dry it at 105oC.

Weight of dish: xg

Weight of dish + clay: yg

Weight of clay = (y-x)g

% of clay in soil = (y-x) x 1000x100

25x20
MECHANIC ANALYSIS

• Mechanical analysis separates the inorganic mineral portion of soil

• Size grade below 2.0mm dia.

Procedure:

• Weight out 100 gm soil sample.

• Take powdered soil samples on the top of the sieve set of different mesh size (2.0
mm sieve set) on the mechanical sieve.

• Shake the mixture for 5 to 15min.

• Weigh the sample retained in each sieve separately.

• Calculate % of sand silt and clay according to international system

WATER HOLDING CAPACITY OF SOIL
• Laboratory method
• Field method

Laboratory method:
• Crush the collected soil sample gently

• Dry the sample in oven at 105oC

• Keep the filter paper (Whatman No.1) inside the perforated bottom of the circular
soil box and weigh the box – W1.

• Fill the box with dried soil and record the weight of box with dried soil – W 2.

• Keep the box in a Petri dish, having water for about 12hrs for saturation of soil.

• Remove the box from the Petri dish and wipe it to dry weigh the box and record
the weight – W3.
Calculation:

Water holding capacity % = (W3-W2)-(W2-W1) x 100

(W2-W1)

Where

W1 = Weight of empty box

W2 = Weight of box with dried soil
W3=Weight of box with water saturated soil
Field method

• Weight the breaker (W1)

• Fill the beaker with dried soil and record the weight (W2)

• Fill the water drop by drop on soil till the soil completely saturated with water
next record the weight in grams – W3.

Calculation:

Water holding capacity W (HC %): (W3-W1)-(W2-W1) x 100

(W2-W1)
SOIL PH
• The pH value of soil is the particles in solution

• Fluctuate due to climate condition, cultivation, crop growth and other factors

• Soil pH is determined using pH meter-potentiometrically

Procedure:
• Take 10 or 20g. of air dried soil sample in screw capped Jar (80-100ml capacity)

• Add 50ml. of distilled water or salt solution

• Screw the lid and keep it on the mechanical shaker and shake for 15min

• Allow the mixture to stand for 30 to 60min. so that soil settles completely

• Measure the pH using pH meter by following standard procedure

• Express results
SOIL CONDUCTIVITY

• Conductivity - ability to transmit electric current using conductivity meter

• Conductivity values - expressed as (millimhos) mmho/cm

• The saturated mixture 2:5 or 1:5 soil:water ratio extract is used for conductivity
estimation
Procedure:

• Take 10 or 20 g. of accurately weighted air dried soil in a wide mouth screw caped
jar

• Add 50ml of distilled water

• Shake the soil mixture on mechanized shaker for 30-60 min.

• Allow the soil particles to settle down completely(30 to 60min)

• Centrifuge at 4000 rpm. for 10 min.

• Filter the supernatant to obtain clear solution

• Place the sensor of conductivity meter in suspension and read the value

• Express results _____ mmho/cm

SOIL ORGANIC CARBON

• Fertility of soil fertility - dependent on the organic carbon contained in the soil

• Principle: The soil organic matter is oxidized under standardized condition with
pot-dichromate in H2SO4

Procedure:

• Take 1.0 gm. of soil sample into a clean 500 ml conical flask

• Add 10.0 ml of 1.0N. Potassium dichromate (K2Cr2O7) and mix well

• Add 20.0ml concentration H2SO4 and allow the mixture under dark for 30min.
• Dilute it with 200 ml distilled water and add 10.0 ml of conc. Phosphoric acid

• Titrate the mixture of excess, pot. dichromate with 0.5N. Ferrous ammonium
sulphate (Fe(NH4)2(SO4)2)using ferrion indicator

• Colour charges blue on addition of indicator and the end point is brilliant green

• Carryout the blak with all reagents but without soil

• Standardize the solution of Ferrous ammonium ssulphate in using standard

potassium dichromate solution following the above procedure
Calculation:

Organic Carbon % = B – A x 0.3

Where,
B = Titration value (ml) of Fe(NH2)2(SO4)2 in blank
A = Titration value (ml) of Fe(NH2)2(SO4)2 with soil

• Note : To over come Chloride ions in the soil, add silver with soil.

• Sulfate solution – organic carbon values between 1.5 – 2.5 % optimum for fish
production; 0.5 % too poor for fish production
SOIL NITROGEN (TOTAL NITROGEN):

• Total nitrogen - forms an important component of soil fertility

• Determined by micro Kjeldhl method

• Principle : The organic matter is oxidized by treating soil with boiling concentrated
H2S04

– Nitrogen converted into ammonium sulphate

– After digestion the mixture is made alkaline and released ammonia is distilled
quantitatively into dilute boric acid and titrated with standard acid
Procedure

• Take 1.0 g of soil sample in Kjeldahl digestion flask

• Add 5 to 10ml distilled water and keep it for 30 min.

• Add 6.0 ml of conc. H2S04. and 2.0g. digestion mixture

• Heat the digestion flash on a heater

• Cool the mixture and make up the volume to 250 ml.in volumetric flask with
distilled water
• Take 10.0ml aliquot of digested mixture in distillation flask

• Neutralize the sample by adding 5.0 ml of 45% NaOH solution

• Collect the distilled ammonia in 10.0 ml 52% boric acid and few drops of mixed
indicator

• Titrate the distillate against 0.01N. H2S04. to get pink color as end point
Calculation

Concentration of N(%) in soil = 0.014 x a x b x 100

Weight of Soil sample
Where,
a. Normality of H2SO4 used in titration

b. Volume of H2SO4 used

• 25 to 75 mg N/100 gm soil ------ indicate the good productivity

• < 25 mg N/100 gm of soil --------- low productivity

LIME REQUIREMENT:

• Liming - application of calcium and magnesium compounds to the soil for the
purpose of reducing the soil acidity

• Liming - stabilizes the pH of the soil

• Lime requirement (LR) denotes the amount of lime required to be added in pond
to bring the pH of the bottom soil to a desirable level
Method

Lime requirement by using buffer solutions

pH of soil : water + buffer
Soil pH

7.9 7.8 7.7 7.6 7.5 7.4 7.3 7.3 7.1

5.7 90 180 270 360 450 540 630 725 820

5.6 125 250 380 500 630 700 880 1010 1130

5.5 200 400 600 810 1010 1210 1410 1610 1810

5.4 290 560 870 1160 1450 1740 2030 2320 2610

5.3 340 680 1020 1360 1700 2040 2380 2720 3060

5.1 440 880 1325 1760 2200 2650 3090 3530 3970

4.9 660 1310 1970 2620 3280 3930 4590 5240 5980

4.8 670 1340 2020 2690 3360 4030 4700 5390 6050

4.7 700 1410 2120 2820 3530 4230 4940 5640 6350
Procedure:

• Weigh 20g of sieved soil sample into 100ml glass beaker

• Add 20ml of distilled water

• Stir intermittently for one hour

• Measure the pH of the soil solution with pH meter

• Add 20ml P-nitro phenol buffer to the soil solution and stir intermittently for 20
minutes

• Set the pH meter to pH 8.0 with 1:1 mixture of P-nitro phenol and d/w

• Measure the pH of the soil solution with constant stirring

• To obtain the liming rate in the table use the pH values of soil sample in distilled
water and buffer solution