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1
INTERNSHIP REPORT
Work completed at
Soil Physics Research ProgramLAND RESOURCES RESEARCH INSTITUTE
NATIONAL AGRICULTURAL REASERCH CENTRE ISLAMABAD
Relationship of Soil Physical & Chemical Properties with Aggregate Stability in Rice-Wheat Soil
Submitted by:
SALEEM ULLAHReg. No. 10-US-AGR-186
Roll No. BAGF10E027
2
Department of Soil & Environmental ScienceUNIVERSITY COLLEGE OF AGRICULTURE
UNIVERSITY OF SARGODHA
LIS T O F CONTENTS
Title Page i
Introduction to Soil Physics Program ii
Research Title 1
Introduction 1
Materials and Methods 3
Results and Discussion 13
Conclusion 14
Table 1 14
Table 2 15
Figure 1 16
Figure 2 17
References 18
3
CERTIFICATE
This is to certify that SALEEM ULLAH (Reg. No. 10-US AGR-186) is a student of department
of Soil science from University College of Agriculture, University Of Sargodha has successfully
completed his internship on, “Relationship of Soil Physical & Chemical Properties with
Aggregate Stability in Rice-Wheat Soil” at Soil Physics laboratory’ Land Resources Research
Institute (LRRI), National Agriculture Research Center (NARC), Islamabad.
Supervisor (s)
Supervisor at NARC: Supervisor at university
Dr. Ghulam Nabi Dr. Ghulam Sarwar
____________________ ___________________
Principal Scientific Officer Head of DepartmentLRRI /NARC University College of agriculture
University of Sargodha
4
5
Dedicate to
My parents
(Mother)
Who guided me to the right path,
Who’s kind and motivative behavior let me able to
accomplish this task.
Especially to
My uncle, Brother & sister who support me
In each step of my life.
6
ACKNOWLEDGMENT
Each and every praise is to almighty “ALLAH” The most kind and merciful, the most beneficent. Who is
entire source of knowledge and wisdom endowed to mankind and countless salutations be Holy Prophet
Muhammad (PBUH), who is forever a true torch of guidance and knowledge for humanity
It gives me great pleasure to acknowledge the consideration of Dr. Ghulam Nabi, PSO/PL,NARC
Islamabad who accepted our request and gave me an opportunity to learn under his guidance.
I would also like to thanks Mr. Shahid Maqsood Gill, PSO, NARC & Mr. Ijaz Ali, SSO, NARC and
Dr. Ghulam Sarwar Head of Department (Soil& Environmental science) who was with me right from
the start till the end and gave me latest information regarding the relevant field, shared knowledge with
me in the form of lectures or discussion which gave me the confidence to perform practical work. I totally
attribute my modest success and achievements I had during this internship to them.
I have no words to express my deepest gratitude and heartiest thanks to Mr. Ghulam Haydar (Lab
Assistant) Soil Physics.
To pen off, I’m very thankful to My parents to MALIK FAIZ ULLAH BOURANA and MALIK
NASAR ULLAH NASIR BOURANA for always being there for me when I needed them, My Soil
Physics Laboratory Internship Fellow especially Ms. Asma Tanveer and Ms. Seemab Liaqat who
shared their wisdom with me, and my fellows Mr. Adeel Ashraf, Syed Hamad Haydar, Saddam
Hussain, Malik Gul Hassan Awan,. Muhammad Tayyab and my seniors Mr Shahid Ul Qadri,
Shahbaz Ali & Osama Baloch and all friends who always wanted me to be successful and shared the
most memorable moments of my life. Their encouragement, helpfulness and support kept me going.
(SALEEM ULLAH)
7
LAND RESOURCES RESEARCH INSTITUTE
NARC
Land Resources Research institute (LRRI), established in 1982, focuses on producing more food
and fiber on less land using fewer inputs while protecting the environment. The proceeding
pages provide an overview of its mandate, accomplishments, services offered and future thrusts.
The Mission
Provide scientific bases for enhancing and sustaining soil productivity and protecting the environment.
Objectives
Conduct strategic soils research to understand soil physical, chemical and biological processes.
Develop technologies for efficient soil input management and environmental protection. Provide technical support to other research organizations, educational institutions, and
relevant industry.
8
INTRODUCTION
Soil aggregates are groups of soil particles that bind to each other more strongly than to adjacent
particles. Aggregate stability refers to the ability of soil aggregates to resist disintegration when
disruptive forces associated with tillage and water or wind erosion are applied. Aggregate
stability suggests how well a soil can resist raindrop impact and water erosion, while size
distribution of aggregates can be used to predict resistance to abrasion and wind erosion.
Changes in aggregate stability may serve as early indicators of recovery or degradation of soils.
Aggregate stability is an indicator of organic matter content, biological activity, and nutrient
cycling in soil. Generally, the particles in small aggregates (< 0.25 mm) are bound by older and
more stable forms of organic matter. Microbial decomposition of fresh organic matter releases
products (that are less stable) that bind small aggregates into large aggregates (> 2-5 mm). These
large aggregates are more sensitive to management effects on organic matter, serving as a better
indicator of changes in soil quality. Greater amounts of stable aggregates suggest better soil
quality. When the proportion of large to small aggregates increases, soil quality generally
increases.
Stable aggregates can also provide a large range in pore space, including small pores within and
large pores between aggregates. Pore space is essential for air and water entry into soil, and for
air, water, nutrient, and biota movement within soil. Large pores associated with large, stable
aggregates favor high infiltration rates and appropriate aeration for plant growth. Pore space also
provides zones of weakness for root growth and penetration. Surface crusts and filled pores
occur in weakly aggregated soils. Surface crusts prevent infiltration and promote erosion; filled
pores lower water-holding and air-exchange capacity and increase bulk density, diminishing the
conditions for root growth.
The size of aggregates and aggregation state can be influenced by different cropping processes
and agriculturalactivities that alter the content of organic matter and the biological activity of the
soil. Over short periods of time,the stability of soil aggregates is modified under the influence of
different cropping treatments, probably beingmore related to changes in the organic constituents
than to the actual total organic matter content .However, over long periodsof time, the stability of
the aggregates diminishes as the organic matter content declines as a result of it being usedas an
energy source by the microorganisms of the soil.
9
Crop systems present a differentiated behavior on soil aggregation. Grasses, due to their
extensive root system, arethe plants that present the greatest effect on the aggregation and the
highest aggregate stability (Harris et al., 1996). On the other hand,the different crop systems
exercise their effects on the formation and stabilization of the aggregates in adifferentiated way
and that depending on the type of cropping and soil use, their effects will be bigger or smaller
interms of degradation. Considering these aspects, the objective of this work was to evaluate the
impact of croprotation and soil management systems on its structural stability, measured from
the distribution of the size of water.
The aggregation is strongly affected by physic-chemical characters of any given soil. Rice wheat
soils are intensively cultivated and are characterized of having low organic matter content. How
its aggregation is related to soil physical characters is not explored. Therefore present study was
undertaken to evaluate the relationship between physic- chemical properties of rice- wheat soil
and soil aggregation parameters.
10
MATERIALS AND METHODS
Soil Sample Description
Soil Physics Research Program, LRRI, NARC had collected soil samples from the rice-wheat
area district Gujranwala and Sheikhupura after harvesting rice during 2011-2012. The samples
had been air dried,prepared and passed through 2mm sieve. The prepared samples had been
stored in Soil Physics Laboratory. The surface soil samples (0-12cm) differing in physic-
chemical character were used in the study reported here.
1. Soil Reaction (pH)
The soil pH is determined to evaluate wither the soil is acidic or alkaline. It is an important soil property
since it directly affects availability of plant nutrients. The ideal pH range for a soil is from 6.5 to 7.5
because most of the nutrients are available in this range. The pH was measured in 1:2 soil to water ratio as
described by (Ryan 2001) as under:
Apparatus:
i. pH meterii. Plastic cups, Beakersiii. Distilled water
i. Soil Extraction
For pH measurement, 10g air dry soil having particle size <2mm was taken into 40 ml glass beaker and
20 ml of distilled water was added using a graduated dispenser. It was mixed well with glass rod and
allowed to stand for 30 minutes. After this the contents were stirred with every 10 minutes interval.
ii. pH Meter Calibration
Before pH measurement, pH meter was calibrated
and standardized with buffer two solutions. The
buffer solution of pH 7.0 and pH 9.2 were prepared
by dissolving respective buffer tablets in 100 ml
distilled water. The pH meter was standardized with
these buffer solution.
For calibration, theelectrode was dipped in buffer
solution of pH 7.0 and reading on meter displaywas
adjusted to exactly 7.0 by rotating pH meter knob.
Then pH electrode was removed from the buffer
11
solution, washed with distilled water and whipped dry with tissue paper then pH electrode was dipped
into second buffer solution of pH 9.2, when stable reading on pH meter display appeared, it was adjusted
to 9.2 by rotating pH meter knob. After adjustment the electrode was removed from the buffer solution
and calibration process was repeated 3-4 times to ensure exact calibration.
iii. Recording of the Reading
After 1 hour the suspension was stirred and electrode of pH meter was dipped 3cm deep into the
suspension and reading was recorded after 30 seconds. After taking the reading the combinedelectrode
was removed from the suspension and rinsed with distilled water and dried with tissue paper thoroughly.
2. Electrical Conductivity
The main objective to determine the EC value is evaluate concentration of total salts present the soil. The
EC value reflectssalinity status of a soil. The Ec was measured in 1:2 soil to water ratio as described by
(Ryan 2001) detailed as under:
For measurement 10g air dry soil having particle size <2mm was taken into 40 ml glass beaker and 20
ml of distilled water was added using a graduated dispensator. The contents were mixed well with glass
rod and allowed to stand for 30 minutes. After this the contents were stirred with every 10 minutes
interval.
Apparatus:
iv. Conductivity meter
v. Plastic cups, Beakers
vi. Standard Potassium Chloride (KCl) Solution (0.01N)
vii. Distilled water
For calibration, a portion of the standard KCl solution was taken in the plastic cup and electrode
of conductivity meter was dipped in it. The instrument was turned on and allowed to settle in the
standard solution for few minutes. Calibration knob was rotated till reading on meter display was
achieved 1.413 mS/cm. After adjustment the conductivity electrode was removed from the
solution and calibration process was repeated 3-4 times to ensure exact calibration.Once
calibration was complete, the conductivity meter was ready for use.
After calibration, the suspension was stirred and electrode of EC meter was dipped deep into the
suspension and reading was taken. After taking the reading the conductivity electrode was removed from
the suspension and the cell was rinsed with distilled water and dried with tissue paper thoroughly and
stored in laboratory for future use.
O.M (%) =(ml for blank – ml for sample)
Weight of Sample ().
X0.069X 0.5
12
3. Soil Organic Matter
Soil Organic matter is defined as a group of carbon containing compounds that have been originated from
living beings (plants parts, roots, macro and microorganism) and deposited on or within the earth surface.
It includes the remains of all plant and animal bodies which have fallen on earth’s surface or purposely
applied by man in any form.
The soilorganic carbon was determined according to Nelson and Sommers(1982) as described by
Ryan etal (2001) as under
Reagents:
a. Potassium Dichromate Solution (K2Cr2O7) 1.0 N
b. Concentrated Sulphuric Acid (H2SO4)
c. Orthophosphoric Acid (H3PO3)
d. Ferrous Ammonium Sulphate solution [(NH4)2 SO4. FeSO4.6H2O]
e. Diphenylamine indicator (C6H6)2NH
Procedure:
For organic matter measurements2g air dry soil having particle size <2mm was taken into 500 ml flask
and 10 ml of 1.N Potassium di Chromatesolution was added using a 10 ml pipet and mixed well. Then 20
ml concentrated Sulfuric Acid (H2SO4) was added by using a dispenser and allowed to stand for 30
minutes.After this about 200 ml of distilled water was added. Then20 ml concentrated Orthophosphoric
acid was added by using a 25 ml glass cylinder and mixture was allowed to cool. Then 10-15 drops of
Diphenylamine indicatorwere added. The color of mixture appearedviolet-blue. The contents were titrated
against 0.5 M Ferrous Ammonium Sulfate solution taken in a buretteuntil color changed to bluish green.
A duplicate set of blank samples was also run in parallel. The soil organic matter was calculated as under:
Where
i. 0.069Correction Factor
ii. 0.5 Molarity of Ferrous Sulphate solution
13
4. Soil CaCO3
Ca Co3 was determined by calcimeter method. Three gram of prepared soil was taken into 500
ml reaction flask and 20 ml of distilled water was added. Then 7 ml of 4 M HCl was taken in a
reaction vial. Reaction vial was carefully shifted into
the reaction flask taking care no HCl in the vial should
spill out. Then the reaction flask was connected to the
Calcimeter in such a way that it attained completely air
tight. The reaction vessel was tilted gently until HCl in
the vial leaked out and reacted with vessel contents. The
carbon dioxide (CO2) produced inside the vessel
developed pressure and pushed the water column in
Calcimeter upward. The water column reading in the
Calcimeter before and after the chemical reaction were
recorded to or work out in rise the water column due to
CO2 determine produced.
A calibration curve of known concentration of CaCo3 was drown to calculate the Ca Co3
contents in the unknown sample.
5. Particle Size Distribution
The particle-size distribution of soil expresses the proportions of the various sizes of
particles which it contains. The proportions are commonly represented by the relative numbers of
particles within stated size classes, or by the relative weights of such classes. The determination
of a particle-size distribution is commonly referred to as a particle-size analysis, a term which
has a largely superseded the older and somewhat ambiguous term “mechanical analysis” (Soil
Sci. Soc. Am.,1946, 1949; Am. Soc. Testing Mater., 1959; Inst. Chem. Eng., 1947, P.114).
Particle-size distribution is one of the most stable soil characteristics, being little
modified by cultivation or other practices. Although the usefulness of particle size analysis in
practical agriculture has sometimes being questioned, its indirect benefits have been extensive. It
has been used in many countries as a basis of soil textural
14
Particle size distribution of <2 mm fractions was measured by the hydrometer method as
described by Gee and Bauder (1986). The hydrometer method measures the particle size on the
differential settling velocities within a cylinder. The procedure consists of two partsi.e dispersion
of sample and sedimentation.
(1) Dispersion
40 g of soil was taken in plastic beaker. 60mL dispersion solution of sodium
hexametaphosphatewere added. Volume was made to 200mL by adding distilled water. The
samples were left overnight. Next day samples were transferred to dispersion cup. Sufficient
distilled water was added in the dispersion cup. The dispersion was carried out by mechanical
shaker for 3 minutes.
(2) Sedimentation
The contents of cup were transferred to 1000ml
cylinder and volume was made up to 1000 ml. The
samples were stirred with the help of plunger. Time
recoding on stop watch was started immediately when
en stirring was stopped. The hydrometer was also
inserted immediately into the cylinder to record first
hydrometer reading after 40 seconds of stirring.After 40
seconds 1st hydrometer reading was taken and
temperature was also noted.The second reading was
taken after 2 hours and then correction factor was
applied according to the Stock’s law.
Calculations
Corrections for Temperature and density:
- If temperature of the sample was higher than 20 ° C, 0.36 units were added to every
hydrometer reading of sample and 0.36 unit were subtracted for every 1° C below 20° C.
CHR= H ±[(T ±20)*0.36]
Where
CHR= Corrected hydrometer reading
15
H= Observed hydrometer reading
The silt+clay in the suspension was calculated using the formula;
% Silt+ clay = (CHRI )−(CHRb)
ODsoil wt x 100
Where
CHR1 is corrected Hydrometer reading 1, (taken after 40 seconds)
CHRb is corrected hydrometer reading for blank
OD soil wt = Oven dry weight of soil used
Similarly clay in the suspension was calculated by
Clay (%) = (CHR 2 )−CHRb
OD soilwt x 100
Where
CHR2 is corrected Hydrometer reading 2, (taken after 2 hours)
CHRb is corrected hydrometer reading for blank
The individual quantities of silt and sand were worked out from the above data as under:
Silt (%) = (silt+clay) – clay
Sand (%) = 100- (silt+clay)
The quantities of sand, silt and clay obtained from these calculations were plottedon USDA Soil
Textural Triangle and the corresponding soil textural classes were obtained.
16
Figure 1. The USDA Soil Textural Triangle
6. Sodium (Na) and Potassium (K)
Sodium and potassium concentration was determine in 1:2 ratio of soil water solutionby Flame
Photometer method (Ryan 2001). The determination comprised of two steps i.e soil extraction
and concentration measurements on flame photometer
Apparatus and reagents:
Extraction flasks
Reciprocating shaker
Whatman 42 Filter paper
Storing bottle
Test tube
Flame photometer
Burretts
17
Reagents:
Lithium chloride (LiCl) 200ppm
i. Soil Extraction
10g air dry soil particle size <2mm was taken into
250 ml conical flask and 20 ml of distilled water was
added using a graduated dispenser and were shaken
samples for 30 minutes on mechanical shaker. After
shaking sample were filter through filter paper
Whatman No.42 and theclear filtrate was received in
the bottle.
Concentration measurement:
One ml of extract was taken into a test tube and 4 ml
of distilled water was added. Then 5 ml of Lithium
chloride (LiCl2) was added and stirred on vortex mixture.
Flame photometer was operated according to the instruction provided for equipment. A series of standard
was run ranging from 0 to 10 ppm for Na+/K separately and astandard curve was drawn. The prepared soil
extract was runin the flame photometer accordingly and Na/K concentration was back calculated from the
standard curve (soil extract)
Na was Calculate by
Na=Absorbance value*Dilution*Dilution factor
6.2 Calcium and Magnesium (Ca+Mg)
Ca and Mg in the extract was determined by titration method according to Richards (1954).
An aliquot of 2 ml from extract was taken by pipet and poured into the china dish. Then 10 drops of
buffer indicator and 2-3 drops of Ericrome black-T and titrate against with 0.01 N EDTA then titrate
until the color changes from red to blue .The dark blue color was end point and note the end point.
Calculation:
Ca+Mg (me/l)=mlof EDTA used x normalityof EDTA
sa mplevolumex 100
Sodium Absorption Ratio (SAR):
18
SAR was calculated by following equation
SAR =Na
√Ca+Mg2
Na, K and Ca,+ Mg are in meq/l
7. Mean Weight Diameter
The method of Kemper and Rosenau (1986) wasused to determine mean weight diameter. A nest
of four sieves (1.00, 0.50,0.25 and 0.125mm) was used for MWD determinations. 40 g of <2.0
mm air-dried soils were put in thetopmost of a nest of four sieves of 1.00, 0.50,,0.25 and 0.125
mm mesh size and pre-soaked for 30 minin deionized water. Thereafter, the nest of sievesand its
contents were manuallyoscillated vertically in tank of waterfor 4 minutes using 4-5 cm amplitude
at the rate of 30 times per minutes. After sieving, thesoil aggregatematerials retained on each
sieve were transferred intobeakers, dried in the oven at 105◦C until steadyweight was achieved.
The percentage ratio of theaggregates in each sieve represents the water-stableaggregates (WSA)
of size classes: >1.00,1.00–0.50, 0.50–0.25 and <0.125 mm.The mean-weight diameter (MWD)
of aggregates was calculated by the equation;
MWD =ƩXiWi
whereXi is the mean diameter of the ithsieve size and Wi is the proportion of the totalaggregates
in the ith fraction. The higherthe MWD values, higher the proportion ofmacroaggregates in the
sample and thereforebetter stability.
19
8. Soil Aggregate Stability
Soil aggregate stability was
determined by wet sieving
apparatus as described
byNimmo and Perkins (2002),
using a single sieve of 0.25
mm. Weight of 4.0 g of 2 mm
air-dried aggregates were
placed on the sieves of Wet
Sieving Apparatus and washed
in cans with distilled water for
3 minutes. Then these cans were replaced with cans with a dispersing solution (containing 2 g
sodium hexametaphosphate/l) and the sieving continued until only the sand particles (and root
fragments) were left on the sieves. Both sets of cans were placed in an oven and dried at 110°C.
After drying, the weight of materials of unstable and stable aggregates was determined.
Aggregate stability was calculated as by the equation
WSA = Wds/(Wds+ Wdw)
where
WSA is the index of water stable aggregates,
Wdsis the weight of aggregates dispersed in dispersing solution (g),
Wdwis the weight of aggregate dispersed in distilled water (g).
20
RESULTS AND DISCUSSION
Physical and chemical characteristics of 15 soils examined are summarized in Table 1. Their
variations and ranges are large enough to depict the degree and nature of the structural stability
to the soil characters
A perusal of the data Table 1, indicated that soil pH value ranged from 7.39 to 9.46 with a
mean value of 8.15. This indicated that majority of the soils had pH values towards higher side
than neutral (pH 7) a preferred value. Similarly, the Ec ranged from 0.088 to 0.77 dSm-1 with a
mean value of 0.321dSm-1. The soil organic matter valued ranged from 0.16 to 1.08 % with a
mean value of 0.64. It is generally believed that soils of Pakistan have organic matter around 0.5
% like other regions of the world occurring in arid and semi arid areas. Our results conform these
observations.
Majority of Pakistan soils are calcareous in nature due to its parent material. In this study
CaCO3 ranged from 0 to 11.25 % with a mean value of 3.2%. The data indicated that 4 out of 15
soils were non calcareous. Sodium adsorption ratio values ranged from 0.61 to 9.57 with a mean
value of 3.71. Mean weight diameter ranged from 0.106 mm to 0.80 mm with a mean value of
0.426 and water stable aggregated ranged from 6.82 to 22.56 % with a mean value of 16.59 %.
Water stable aggregates ranged from 6.82 to 22.56 % with a mean value of 16.59 %. The soil
under study ranged from medium (loam) to fine textured (clay loam) and majority of them were
heavy textured.
The linear correlation coefficient between various soil parameters and stability indicators
examined is presented at Table 2. The data Table 2 indicated that a strong correlation existed
between soil organic matter and soil pH. Similarly a very strong positive relationship was
observed for soil organic matter and mean weight diameter as well as for water stable aggregates
as depicted in Figure 1. A negatively strong relationship existed between soil pH and mean
weight diameter as well as for water stable aggregates. A non-significant correlation was
observed between SAR and CaCO3 for mean weight diameter and water stable aggregates
(Figure 2) however a significant positive relationship existed between clay and mean weight
diameter. The lower stability with clay fraction may be due to clay type as smectite and
21
illiteclays have lower cementing properties (Kaewano et.al., 2009). A negative but strong
relationship was observed for sand and mean weight diameter (Figure 2)
CONCLUSION
Soil aggregate stability is an important property of soil since it affects sustainability and crop
production. Intensively cultivated rice–wheat soils under report depicted a wide range of
variations in pysico-chemical character and their relationship with aggregate stability parameters.
Based upon the results it can be concluded that stability parameters are strongly related to soil
organic matter status of soil as well as soil texture. Maintaining of high organic matter levels is
essential to improve higher aggregation.
Table 1. Minimum, maximum, mean and coefficient of variation in measured parameter of 15 examined Soil
pH(1:2)
Ec (1:2)
d Sm-1
OM (%)
Lime (%)
SARMWD(mm)
WSA (%)
Sand (%)
Silt (%)
Clay (%)
Minimum 7.39 0.088 0.16 0.00 0.61 0.106 6.82 12.10 16.00 20.00
Maximum 9.46 0.77 1.08 11.25 9.57 0.800 22.56 64.00 59.80 38.10
Mean 8.15 0.321 0.64 3.20 3.71 0.426 16.59 35.54 37.38 27.08
CV (%) 7.10 58.24 39.89 115.72 76.51 50.60 29.27 43.32 34.17 24.29
22
Table 2. Linear Correlation Coefficient between structure stability indicator and soil characteristics
pH
(1:2)
Ec
(1:2)
OM
(%)
MWD
(mm)WSA (%)
SARLime (%)
Clay (%)
Ec(1:2)0.437ns0.103
_ _ _ _ _ _ _
OM (%)0.0646**0.009
0.0100.972ns
_ _ _ _ _ _
MWD-0.738**0.002
-0.1030.714ns
0.949**
0.000_ _ _ _ _
WSA (%)
-0.579**0.024
-0.014
0.961ns0.531*0.042
0.579*0.024
_ _ _ _
SAR0.025 ns0.928
-0.475*0.073
0.127 ns0.651
0.173 ns0.537
-0.2430.384ns
_ _ _
Lime (%)
0.688**0.005
0.798**0.000
-0.2820.308ns
-0.3580.190ns
-0.208
0.458ns-0.446*0.096
_ _
Clay
(%)-0.0129*0.0646
0.0260.927ns
0.3930.148ns
0.465*0.080
0.4190.120ns
0.0340.905ns
0.1970.481ns
_
Silt
(%)-0.561**0.030
0.411 ns0.128
0.732**
0.0020.692**0.004
0.4330.107ns
-0.2080.457ns
-0.0070.979ns
0.1820.516ns
Sand (%)
0.05210.047ns
-0.3520.198ns
-0.755**0.001
-0.733**0.001
-0.538*0.039
0.158 ns0.573
-0.078ns0.782
-0.578*0.024
** = P-value significant at 5% probability level* = P-value significant at 10% probability levelns= non-significant
23
0.00 0.20 0.40 0.60 0.80 1.00 1.200.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
f(x) = 0.800145041395989 x − 0.0795045293546883R² = 0.900655215047508
Organic Matter (%)
Mea
n W
eigh
t Dia
met
er (m
m)
0.00 0.20 0.40 0.60 0.80 1.00 1.200
5
10
15
20
25
30
f(x) = 15.9241060180077 x + 6.44563474515747R² = 0.577940167910289
Organic matter (%)
Wat
er S
tabl
e ag
greg
ates
(%)
Figure 1. Relationship between organic matter and mean weight diameter and Water stable
aggregates
24
0.00 0.20 0.40 0.60 0.80 1.00 1.200.0
2.0
4.0
6.0
8.0
10.0
12.0
f(x) = 1.41311314565601 x + 3.01759004639313R² = 0.0162555422886347
Organic matter(%)
Sodi
um A
dsor
ptio
n R
atio
(SA
R)
0 10 20 30 40 50 60 700.00
0.20
0.40
0.60
0.80
1.00
f(x) = − 0.0108288621864918 x + 0.818849433512524R² = 0.59708711553771
Sand (%)
Mea
n w
eigh
t dia
met
er (m
m)
Figure 2. Relationship between organic matter and mean weight diameter and water stable
aggregates
25
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SSSA, p317-328.
Richards 1954. Diagnosis and Improvements in Saline and Alkalis. USDA, Handbook 60.
Ryan J., G. Estefan and A. Rashid. 2001. Soil and Plant Analysis; Laboratory Manual 2 nd Edition,
ICARDA
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