Interpreting Soil Tests
•
•
•
•
•
1.
2.
3.
4.
5.
What analytes
What do they mean
Value of them, cost, etc.
How frequent do I test?
Sampling procedure.
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• developed in
1869
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Essentiality
1. Element is essential for plant to complete
its life-cycle.
2. Role of the element must be unique.
3. Essentiality is universal among plants.
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Inputs
Fertiliser
Water
Natural weathering
Atmospheric fixation
Crop residues
Carbon
Outputs
Leaching
Run-off
Crop removal
Residue removal
Burning
Carbon
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Essential Nutrients
•
16 mineral nutrients known to be essential
for plant growth (17 including Si for cane)
• Major nutrients
» (macronutrients – primary & secondary)
• Minor nutrients
» (micronutrients or trace elements)
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Dynamic Equilibria occurring in soils
Nutrient
Uptake by
Plants
Organic matter
and
8
1
2
3
Soil solution
microorganisms
7
Exchange and
surface
adsorption
4
6
5
Crystalline minerals
and properties
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Analyte
Depth (cm)
Organic Carbon %
Colour
Texture
pH (water)
pH (CaCl)
Nitrate nitrogen mg/kg
Sulfate sulfur mg/kg
Phosphorus (colwell) mg/kg
Potassium meq/100g
Calcium meg/100g
Magnesium meq/100g
Sodium meq/100g
Chloride mg/kg
Copper mg/kg
Zinc mg/kg
Manganese mg/kg
Iron mg/kg
Cation Exchange Capacity (CEC) meq/100g
Calcium/Magnesium Ratio
Electrical Conductivity (Sat. Extract)
Sodium % Cations
Result
15 - 60
60 - 90
med. Clay
7.7
6.7
12.6
26
11
0.3
17.95
11.1
2.6
165
0.9
< 0.1
12
20
med. Clay
8.3
7.6
6.3
125
7
0.21
18.03
13.64
5.22
276
0.8
< 0.1
6
16
med. Clay
7.8
7.7
1.4
2520
7
0.25
55.31
14.65
6.51
381
0.6
0.1
2
9
31.95
1.62
0.7
8.15
37.1
1.32
2.8
14.08
76.72
3.78
22.3
8.49
0 - 15
1.1
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Soil pH and nutrient availability
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Soil pH
• pH is measured on a logarithmic scale
– A one-unit decrease or increase in pH is a
tenfold change in acidity or alkalinity
• pH water 7 is neutral
– pH 6 is 10 times more acidic than pH 7
– pH 5 is 100 times more acidic than pH 7
– pH 4 is 1000 times more acidic than pH 7
– this does not mean a log increase in lime rates
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Analyte
Depth (cm)
Organic Carbon %
Colour
Texture
pH (water)
pH (CaCl)
Nitrate nitrogen mg/kg
Sulfate sulfur mg/kg
Phosphorus (colwell) mg/kg
Potassium meq/100g
Calcium meg/100g
Magnesium meq/100g
Sodium meq/100g
Chloride mg/kg
Copper mg/kg
Zinc mg/kg
Manganese mg/kg
Iron mg/kg
Cation Exchange Capacity (CEC) meq/100g
Calcium/Magnesium Ratio
Electrical Conductivity (Sat. Extract)
Sodium % Cations
Result
15 - 60
60 - 90
med. Clay
7.7
6.7
12.6
26
11
0.3
17.95
11.1
2.6
165
0.9
< 0.1
12
20
med. Clay
8.3
7.6
6.3
125
7
0.21
18.03
13.64
5.22
276
0.8
< 0.1
6
16
med. Clay
7.8
7.7
1.4
2520
7
0.25
55.31
14.65
6.51
381
0.6
0.1
2
9
31.95
1.62
0.7
8.15
37.1
1.32
2.8
14.08
76.72
3.78
22.3
8.49
0 - 15
1.1
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Exchangeable Cations, and
Cation Exchange Capacity
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What is Cation Exchange Capacity - CEC?
• ion = atom with charge (+ or -)
• ion -ve charge = anion
•
e.g. NO3- SO42- Cl- H2PO4- MoO42-
• ion +ve charge = cation
• e.g. K+ Na+ Ca++ Mg++ Al+++ NH++++
•
Mn++ Fe++ Cu++ Zn++ Fe+++
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Cation Exchange Capacity
Cations are attracted to negatively charged soil particles and OM
Al+++ Mg++
Ca++
K+ Ca++
Ca++
++
Mg
Al+++
Na+
- ve
- ve
- ve - ve
Mg++
Ca++
K+Mg++ Al+++ Na+
Ca++
++
K+ Ca++ Mg
- ve
- ve - ve
- ve
++
- ve
Ca
- ve
ve
- ve
ve
- ve Soil Colloid - ve
- ve
Na+
ve
ve
- ve - ve Ca++
- ve
ve
- ve
- ve
- ve - ve
- ve - ve
Mg++
ve
Mg++
ve
ve
+
- ve
K
Ca++ Na+ Ca++ - ve
Ca++
Ca++
++
+
Mg
K
K+
Mg++ Ca++
Al+++
Mg++
K+
+ Na
Ca++ K
+
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Calculating exchangeable %
Cation
Value (cmol(+)/kg)
% of ‘Effective CEC’
Calcium (Ca2+)
16.3
62.93*
Magnesium (Mg2+)
6.7
25.87
Potassium (K+)
1.6
6.18
Sodium (Na+)
1.3
5.02
0
0
Aluminium (Al3+)
Total (‘Effective CEC’)
or meg/100gms
25.9
Calcium (% of CEC) = 16.3/25.9 x 100 = 62.93
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Converting Ex Cations:
mg/kg to cmol(+)/kg
Aluminium:
20mg/kg divided by 90 = 0.22 cmol(+)/kg
Calcium:
3200mg/kg divided by 200 = 16.0 cmol(+)/kg
and visa versa: to convert cmol(+)/kg to mg/kg, multiple by figures in table
mg/kg = cmol(+)/kg x Eq. wt. x 10
E.g. Potassium:
117 mg/kg = 0.3 cmol(+)/kg x 39.1 x10
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Analyte
Depth (cm)
Organic Carbon %
Colour
Texture
pH (water)
pH (CaCl)
Nitrate nitrogen mg/kg
Sulfate sulfur mg/kg
Phosphorus (colwell) mg/kg
Potassium meq/100g
Calcium meg/100g
Magnesium meq/100g
Sodium meq/100g
Chloride mg/kg
Copper mg/kg
Zinc mg/kg
Manganese mg/kg
Iron mg/kg
Cation Exchange Capacity (CEC) meq/100g
Calcium/Magnesium Ratio
Electrical Conductivity (Sat. Extract)
Sodium % Cations
Result
15 - 60
60 - 90
med. Clay
7.7
6.7
12.6
26
11
0.3
17.95
11.1
2.6
165
0.9
< 0.1
12
20
med. Clay
8.3
7.6
6.3
125
7
0.21
18.03
13.64
5.22
276
0.8
< 0.1
6
16
med. Clay
7.8
7.7
1.4
2520
7
0.25
55.31
14.65
6.51
381
0.6
0.1
2
9
31.95
1.62
0.7
8.15
37.1
1.32
2.8
14.08
76.72
3.78
22.3
8.49
0 - 15
1.1
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The Nitrogen Cycle
Urea
• It is Nitrogen in the organic form
• Can add 3 days to the process
before it becomes plant available
• Is NOT plant available
• Requires microbial action to
convert to Ammonia
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Nitrogen Pathway
Urea
Ammonia
NH 3
This step can add
an extra 3 days for
your nitrogen to
become plant
Ammonium
NH4: quite
stable, is
fixed onto
the soil
clays
Nitrite:
NO 2 an
intermediate
step and
easily lost in
wet soil, toxic
if allowed to
accumulate in
the plant.
Nitrate: NO 3
plant available
form, also very
soluble and
therefore
subject to
leaching
available
Converted by
natural
soil bacteria
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Nitrogen Balance Sheet
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Analyte
Depth (cm)
Organic Carbon %
Colour
Texture
pH (water)
pH (CaCl)
Nitrate nitrogen mg/kg
Sulfate sulfur mg/kg
Phosphorus (colwell) mg/kg
Potassium meq/100g
Calcium meg/100g
Magnesium meq/100g
Sodium meq/100g
Chloride mg/kg
Copper mg/kg
Zinc mg/kg
Manganese mg/kg
Iron mg/kg
Cation Exchange Capacity (CEC) meq/100g
Calcium/Magnesium Ratio
Electrical Conductivity (Sat. Extract)
Sodium % Cations
Result
15 - 60
60 - 90
med. Clay
7.7
6.7
12.6
26
11
0.3
17.95
11.1
2.6
165
0.9
< 0.1
12
20
med. Clay
8.3
7.6
6.3
125
7
0.21
18.03
13.64
5.22
276
0.8
< 0.1
6
16
med. Clay
7.8
7.7
1.4
2520
7
0.25
55.31
14.65
6.51
381
0.6
0.1
2
9
31.95
1.62
0.7
8.15
37.1
1.32
2.8
14.08
76.72
3.78
22.3
8.49
0 - 15
1.1
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Fertilisers and acid soils
• Fertiliser selection and management play an important
role in arresting acidification
• Nitrogen fertilisers can be acidifying
• As NH4+ is converted to NO3-,
H+ is produced
Ammonium (NH4+) + Oxygen
Nitrifying bacteria
CO2 + S + O2 + 2H2O
Nitrate (NO3-) + 2 H+
CH2O + SO42- + 2H+
Thiobacillus
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Soil Phosphorus Fractions
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Phosphorus Buffering Index
Amount of P fertiliser required to raise soil P by one mg/kg, 6-12 months
after application, according to its P buffer index (PBI)
PBI
PBI Class
kg P to raise
Olsen P
1mg/kg
kg P to raise
Colwell P
1mg/kg
< 36
Very Very Low
5
2.0
36 - 70
Very Low
7
2.0
71 - 140
Low
9
3.0
141 - 280
Moderate
11
3.0
281 - 840
High
13
4.0
> 840
Very High
15
4.0
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Predicted critical Colwell P soil test values for
Standard PBI categories.
PBI category
<15
15-35
36-70
71-140
141-280
281-840
>840
Extremely low
Very very low
Very low
Low
Moderate
High
Very High
Source: Better Fertiliser Decisions for Grazed Pastures
Critical value for mid
point PBI category
(range)
23 (20-24)
26 (24-27)
29 (27-31)
34 (31-36)
40 (36-44)
55 (44-64)
na
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Phosphorus (Colwell) mg/kg
35
31
30
29
25
23
20
21
Phosphorus (Colwell)
18
17
Lower
15
Upper
12
10
5
0
2006
2007
2008
2009
2010
2011
2012
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Electrical Conductivity EC
• Definition: a measure of the conductivity of
electricity through water. The value reflects
the amount of soluble salts in an extract and
therefore provide an indication of soil salinity.
• Electrical Conductivity dS/m
• Electrical Conductivity (saturated extract)
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Saline soils
• Salinity is the presence of soluble salts in the plant
root zone or on the soil surface at a concentration high
enough to impact plant growth
• In Australia, soil salinity is predominantly due to salts
of sodium: NaCl, Na2CO3 & NaHCO3
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What is a salt ?
• By the combination of an acid and a base, the
hydrogen of the acid is replaced by the metal
of the base, and the result is the formation of
a salt.
• HCI + NaOH = NaCI + H2O
• Acid base
salt water
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• developed in
1869
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Measuring soil salinity
• Soil salinity is commonly measured as the electrical conductivity
(EC) of soil water
•
EC is often given in units of deci-Siemens per metre (dS/m) and
is measured in soil using two methods:
– Saturated paste extract (ECse) – most accurate, or
– 1:5 soil:water extract (EC1:5) – most commonly used
– It’s important to know which measurement is taken, as the different
methods give different results
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NUTRIENT
Sulfate Sulphur
0-10cm
10-30cm
30-60cm
60-90cm
90 -115cm
Calcium
0-10cm
10-30cm
30-60cm
60-90cm
90-115cm
Magnesium
0-10cm
10-30cm
30-60cm
60-90cm
90-115cm
Sodium
0-10cm
10-30cm
30-60cm
60-90cm
90-115cm
Chloride
0-10cm
10-30cm
30-60cm
60-90cm
90-115cm
No. 1
No. 2
Medium Clay Soil
% Change Sandy Clay Soil
% Change
23.12.2005 28.8.2006
23.12.2005 28.8.2006
3.4
6.9
4.6
11
200
220
5,882.35
3,188.41
2.4
3.4
3.8
3.8
200
120
8,333.33
3,529.41
24
27
21
13
17
23
70.83
85.19
6
13
17
17
4.9
4
81.67
30.77
9.1
12
12
12
7.7
11
84.62
91.67
2.7
6.4
8.2
9.9
1.4
1.7
51.85
26.56
2.3
5.7
8.3
10
7.4
5.2
321.74
91.23
0.52
2
3.7
6.1
3.6
2.1
692.31
105.00
17
5.7
550
800
460
480
2,705.88
8,421.05
10
18
76
130
310
270
3,100.00
1,500.00
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NUTRIENT
No. 1
No. 2
Medium Clay Soil
% Change Sandy Clay Soil
% Change
23.12.2005 28.8.2006
23.12.2005 28.8.2006
C.E.C. (Cation Exchange Capacity)
0-10cm
10-30cm
30-60cm
60-90cm
90-115cm
Ca:Mg
0-10cm
10-30cm
30-60cm
60-90cm
90-115cm
E.S.P % (Exchangeable Sodium Percentage)
0-10cm
10-30cm
30-60cm
60-90cm
90-115cm
E.C.ds/m (Electrical Conductivity)
0-10cm
10-30cm
30-60cm
60-90cm
90-115cm
36
45
41.6
35.3
32.9
39.7
91.39
88.22
9.66
21.6
29
33.1
10.6
8.2
109.73
37.96
2.5
2.3
1.8
1.1
2.2
2.1
88.00
91.30
2.2
2
2.1
1.7
3.5
2.4
159.09
120.00
6.4
13
20
28
22
13
343.75
100.00
5.4
9.3
13
18
34
26
629.63
279.57
1.2
2.1
4.2
5.4
6.6
6.6
550.00
314.29
0.4
1.5
2.2
3.1
5.7
3.2
1,425.00
213.33
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Natural soil variability with depth
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Sampling method
Zig-zag
B
A
Transect
C
Zone
Cluster
Grid
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SAMPLING; most errors occur here in practice
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Soil Nitrate - Number of Cores
Confidence Level
Number of cores needed for
Medium accuracy
Nitrate N+/- 20% of mean Water +/- 2%
66%
3
2
80%
5
3
90%
8
5
Higher level
66%
80%
90%
Nitrate N +/- 10% of mean
10
18
29
Water +/- 1%
7
12
20
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Analyte
Depth (cm)
Organic Carbon %
Colour
Texture
pH (water)
pH (CaCl)
Nitrate nitrogen mg/kg
Sulfate sulfur mg/kg
Phosphorus (colwell) mg/kg
Potassium meq/100g
Calcium meg/100g
Magnesium meq/100g
Sodium meq/100g
Chloride mg/kg
Copper mg/kg
Zinc mg/kg
Manganese mg/kg
Iron mg/kg
Cation Exchange Capacity (CEC) meq/100g
Calcium/Magnesium Ratio
Electrical Conductivity (Sat. Extract)
Sodium % Cations
Result
15 - 60
60 - 90
med. Clay
7.7
6.7
12.6
26
11
0.3
17.95
11.1
2.6
165
0.9
< 0.1
12
20
med. Clay
8.3
7.6
6.3
125
7
0.21
18.03
13.64
5.22
276
0.8
< 0.1
6
16
med. Clay
7.8
7.7
1.4
2520
7
0.25
55.31
14.65
6.51
381
0.6
0.1
2
9
31.95
1.62
0.7
8.15
37.1
1.32
2.8
14.08
76.72
3.78
22.3
8.49
0 - 15
1.1
And we can save 700 Lira by not taking Soil Tests.
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Any Questions ?????
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The Function of Organic Material in
Soils.
• 1. Organic Matter
• 2. Organic carbon, nitrogen, phosphorus and
sulphur, etc.
• 3. How does the process work?
• 4. Efficiency of process
• 5. Process drivers
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Organic matter
• Usually < 5% of the soil mass
• Strongly influences the physical and chemical
properties of soils
• Decomposition is more rapid in warmer wetter
climates.
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Functions of organic matter
Stabilising agent – soil porosity
Decreases erosion
Reduces the effects of sodicity
Improves water infiltration and holding capacity
Supplies plant nutrients
Moderates extreme soil temperatures
Buffers against rapid changes in salinity, sodicity, and
pH
• Energy and nutrient for micro-organisms
• Adds to CEC of soil
•
•
•
•
•
•
•
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Decomposition of Organic Matter
Influenced by:
•
•
•
•
•
•
•
•
Type of material – fragile or not
Composition – C:N ratio, chemicals, animal or plant
Age and moisture content
Soil oxygen status – aerobic or anaerobic
Crop rotations – legumes
Tillage options – cultivation levels
Soil type – soil pH
Soil temperature and moisture
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Carbon Cycle
+3.3 Gt/year
Decay
losses
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5 major soil carbon pools
•
. Living organisms and roots (labile)
<5%
•
2. Soluble - fresh residues (labile)
<10%
•
3. Particulate organic C -decomposing (labile)
•
4. Humus (decadal)
•
5. Charcoal/Resistant (inert)
10-50%
33-50%
1-30%
• *Adapted from Skjemstad & Baldock
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Composition of soil organic carbon
• Crop residues on the
soil surface (SPR)
• Buried crop residues
(>2 mm) (BPR)
• Particulate organic
matter (2 mm –0.05
mm) (POC)
• Humus (<0.05 mm)
(Hum C)
• Resistant organic
matter (ROC)
• Extent of decomposition
increases
• Rate of decomposition
decreases
• C/N/P ratio decreases
(become nutrient rich)
• Dominated by charcoal
with variable properties
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Nitrogen Losses
• Leaching
• Denitrification
• Immobilisation
• Volatilisation
• Run-off
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“ Good news bad news ” story
• Immobilisation
Mineralisation
• Immobilisation
Mineralisation
• Immobilisation
Mineralisation
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Nitrogen Pathway
Urea
Ammonia
NH 3
This step can add
an extra 3 days for
your nitrogen to
become plant
Ammonium
NH4: quite
stable, is
fixed onto
the soil
clays
Nitrite:
NO 2 an
intermediate
step and
easily lost in
wet soil, toxic
if allowed to
accumulate in
the plant.
Nitrate: NO 3
plant available
form, also very
soluble and
therefore
subject to
leaching
available
Converted by
natural
soil bacteria
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Nitrifying bacteria
Nitrosomonas
Nitrobacter
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Any Questions ?????
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