Soils 206 -52
09 DEC 03
Introduction: The purpose of this report is to review and evaluate data which
was gathered in lab. The areas which we will evaluate are: Cation Exchange Capacity
(CEC); salt-affected soils; soil organic matter and pH; nitrogen; and soil survey and
Geographical Information System (GIS). By analyzing these soils, a better understanding
of their formation can be gained.
Methods and Results: To obtain the data, a variety of methods were used.
Obtaining the CEC involved three parts: 1) Saturating all the exchange sites with a
known cation. For this we used H+; 2) Replacing all of the cations on the exchange sites.
Ca2+ was used to displace the H+ cations on the exchange sites; 3) Quantify (measure) the
displaced cations. When measuring the CEC we used the two soils, Devoignes and
Quincy and started with 5 grams of each soil. Quincy, which is a sandy soil, resulted in a
low CEC of 10, compared to Devoignes which is finely textured and having a high CEC
of 107 (appendix a, figure a-1).
We classified a salt-affected soil as either saline, sodic, or saline-sodic, or how
much sodium vs. calcium, based on the EC, ESP (appendix a, figure a-2), and the PH of
the soil. Through this we decided whether the soil would need reclamation or not, and
decided what the best method of reclamation should be. First we saturated the soil with
the initial saturating reagent NaCl. We then leached the soil with the first leaching
reagent, NaCl and then the second leaching reagent DI water.
The two soils Latacho and UVI were measured for pH and soil carbon and
organic matter. To obtain the pH of the two soils we first put 10g of each soil into
separate plastic cups and added 10 ml of deionized water to each. We then mixed both
cups and allowed them to stand for 10 minutes. We determined the pH of the suspension
with a calibrated pH meter. Latacho had a pH of 5.19, while UVI had a pH of 6.15. Based
on the pH of the soil we could then calculate the liming requirements (appendix a, table
a-3). The total carbon and nitrogen in our soils was measured by dry combustion using a
C/N/S analyzer. The total carbon measurement consists of both organic and inorganic
1
forms. A ground soil sample was heated to approximately 1000o C in a sealed
combustion tube. Both carbon dioxide and nitrogen gases are analyzed by an interlan
thermal conductivity detector and the computer calculates the %C %N, and the C:N ratio
of the soils (appendix a, table a-4). Latacho contained 145.7% carbon and 10.3%
nitrogen, while UVI contained 28.6% carbon and 1% nitrogen. This resulted in a 14:1
C:N ratio for Latacho and a 28.6:1 C:N ratio for UVI.
To observe the nitrogen cycle process we incubated a soil under various
treatments for a period of 4 weeks (appendix a, figure a-6). All jars were covered with
saran wrap and perforated to allow oxygen to enter the jar. Additional water was added to
the anaerobic jar in order to keep it saturated and was not oxygenated as the other jars
were through perforated holes. The jars were checked approximately midway through
their incubation period to ensure proper moisture was available. The content of the jars
was also thoroughly mixed at this time. Because the lab ran out of test strips to measure
the nitrate and nitrite concentration we did not finish the lab to attain our results.
However, we do have expected data for the six jars (appendix a, table a-7)
Discussion: The relatively high CEC of Devoignes suggests that its colloidal
fraction is a 2:1 type clay (constant charge) compared to Quincy’s low CEC, which
would make it a 1:1 type clay (pH dependant charge). The high amount of organic matter
or humus contained in Devoignes was probably a factor contributing to the high CEC.
Quincy would not have appreciable permanent net negative charge compared to
Devoignes which would have a high net negative charge. Devoignes would as well have
a higher nutrient availability than Quincy due to the difference in CEC.
Salt affected soils are classified using electrical conductivity (EC), exchangeable
sodium percentage and pH measurements as saline, sodic or saline-sodic. After the first
leaching treatment the EC went up, but after the second leaching treatment the EC started
to drastically increase, suggesting that the soil was changing from flocculated to
dispersed allowing better infiltration due to less macropores (appendix a, figure a-5).
Of all soil chemical variables pH is the most important, influencing properties as
diverse as nutrient availability, the functioning of micro-organisms and the fate of many
pollutants as well as soil quality. Since Latacho had a pH of 5.19 which is relatively close
to 5 it could contain soluble aluminum in amounts that would be toxic to some plants.
2
With UVI’s pH at 6.15 it would provide conditions which would be best overall for
optimizing nutrient availability. Pollutants which could contribute to soil acidity would
be chemical fertilizers and organic wastes. Active, exchangeable and residual are three
types of acidic soils. The ability for these soils to resist changes in pH would be their
buffering capacity.
Immobilization refers to the process where decomposition and nutrient cycling
stops, and nitrogen is scavenged from the soil making it unavailable to the plants (C:N
>24:1). Because Devoignes has as C:N ratio of 28.6:1 it would fall into this category.
When there is more nitrogen than is needed for cellular growth the nitrogen is
mineralized (C:N < 24:1) such as in the case of the Quincy soil which has a C:N ratio of
14:1. As the organisms eat the organic material about 66% of the carbon is lost as CO2
through respiration.
There are three forms of nitrogen in the soil; organic nitrogen, ammonium
nitrogen, and soluble inorganic nitrogen. Organic nitrogen makes up the bulk (95%) of
the nitrogen in the soil and is also a product of immobilization from the inorganic or
NH4+ form to the organic form. This was the intended result of the jar containing
sawdust. Because the sawdust has a high C:N ratio (greater than 24:1) soil
microorganisms (a variety of chemoautotrophic actinomycetes, fungi, and bacteria) could
not break it down without requiring excess nitrogen in the form of NH4+ from the soil.
Mineralization is the conversion of organic nitrogen into inorganic nitrogen.
Mineralization was expected to be seen in the B. napus and B. juncea jars. The low C:N
ratio of the B. napus and the B. juncea (less than 24:1) allowed the soil microorganisms
to break it down without requiring excess nitrogen from the soil. This allowed them to
convert the organic nitrogen into inorganic nitrogen thus making it a usable form for
plants. The process of nitrification is the enzymatic oxidation of ammonium to nitrate and
is performed by chemoautotrophic bacteria. This was what was expected from the jar
containing (NH4)2SO4. Denitrification involves the loss of nitrogen to the atmosphere
when nitrate ions are converted to gaseous forms of nitrogen. This process is carried out
by anaerobic bacteria (autotrophic which makes its own food and heterotrophic which
feeds on other organisms) and was the intended result of the anaerobic jar containing B.
juncea. The conditions which favor this type of reaction are the presence of nitrate,
3
readily decomposable organic matter (B. juncea), soil air with less than 10% oxygen
(non-perforated saran wrap), and a soil temperature between 25 and 35 degrees Celsius.
A soil survey can be used to gain information and data about the use and
management of the soil as well as the capabilities and limitations. Soil mapping units
represent the boundaries between different soil series. The rectangular survey system is
the basis for location of a particular tract of land and is also called the township-range
system. The Universal Transverse Mercator (UTM) is often used as a coordinate system
in GIS. The UTM is also used as a map projection to overcome the problem of portraying
a spherical surface of the earth onto a planer surface. Some management uses of GIS
would be that of defining property lines. GIS also has many engineering uses through a
graphical representation to gain vegetation information. In the fisheries discipline, which
is my field of study, GIS is used to obtain stream data for an area which can be used prior
to field research being conducted. GIS can also be used after stream data is collected, as a
graphical representation of what data was found where.
Conclusion: The CEC of a soil can be used to help determine soil chemistry and
the study of colloids. This data can then be useful in the determination of the potential
use of a soil. While the CEC of Devoignes was higher than expected it is still within the
range of CEC for this soil, therefore the data cannot be discounted. Identification of salt
affected soils can be used to determine reclamation procedures which help in determining
the ability of the soil to be productive for a variety of uses. All data taken was within the
expected values. Soil organic matter and pH can be obtained to determine soil quality
through the percentages of nitrogen and carbon to determine the C:N ratio. The C:N ratio
can tell you whether the quality of the soil would suit certain vegetation as well as
support microbial growth. The C:N ratio for Latacho was relatively low suggesting that
the data was incorrect. This experiment should probably be done again in order to
confirm or deny this C:N ratio. While we did not get to finish the nitrogen experiment,
expected values were used and concepts were applied. Time, microbial activity and
nitrate levels are what drive the nitrogen cycle. Soil survey and GIS is used by a variety
of disciplines such as engineering, ranching, agronomists, farmers and foresters just to
name a few. The information which they can access using GIS can aide them in many
ways including definition of property lines, vegetation, slope etc.
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Appendix a
5
a-1
Weight (g)
NaOH (ml)
NaOH (N)
CEC (cmolc)
Devoignes
5
53.5
.1
107
Quincy
5
5
.1
10
Soil Name
CEC CALCULATION FOR QUINCY
5
.1
ml NaOH
g Soil
5
*
1 molc
1L
mol NaOH
L
*
1 mol NaOH
*
1000 ml
*
100 cmolc
1 molc
*
1000 g
1 kg
10
=
cmolc
kg soil
CEC CALCULATION FOR DEVOIGNES
.1
53.5 ml NaOH
5
g Soil
*
mol NaOH
L
1 molc
1L
*
1000 ml
*
*
1 mol NaOH
100 cmolc
1 molc
1000 g
*
1 kg
=
107 cmol
c
kg soil
a-2
Calculate the percent exchangeable sodium to be replaced and then the total CEC of
the soil that is to be replaced in cmolc
23%
*
60%
30 cmolc
=
=
1kg soil
4.2 cmolc
1kg soil
Next, calculate the kilograms CaSO4 for each kilogram of soil
4.2 cmolc
1kg soil
*
1 molc
100 cmolc
*
1 mol CaSO4
2 molc
*
136 g CaSO4
1 mol CaSO4
1 kg
*
1000 g
=
2.8X10-3 kg
1 kg soil
Finally, calculate the kilograms CaSO4 for each hectare-15 cm of soil
2.8X10-3 kg CaSO4
1 kg soil
2X106 kg soil
*
1 ha-15cm
=
5600 kg CaSO4
1 ha-15cm
6
a-3
Calculate the percent exchangeable acidity and then convert this value to cmolc of
exchangeable acidity.
.80 Exchangeable acidity
25 cmolc
*
1kg soil
20 cmolc
=
1kg soil
Convert the cmolc to grams of CaCO3 per kilogram of soil.
20 cmolc
1 kg soil
*
1 molc
100 cmolc
*
1 mol CaCO3
2 molc
*
100 g CaCO3
1 mol CaCO3
=
10 g CaCO3
1 kg soil
Convert the units to lb CaCO3 per ac-ft of soil
10 g CaCO3
1 kg soil
454 g
2X106 lb soil
1 kg
1 lb
*
*
2.2 lb
*
1 ac-ft soil
=
20,024 lb CaCO3
1 ac-ft soil
a-4
Soil Carbon and Nitrogen Properties.
Soil name or Type
Carbon (%)
Nitrogen (%)
C:N Ratio
Latacho
1.457
0.103
14 : 1
UVI
0.286
0.01
28.6 : 1
7
a-5
Combined Leachate of 1st Treatment
4 = min 7&8 5 = min 9&10
1 = min 1&2
2 = min 3&4
3 = min 5&6
mL
51
50
46
50
44
EC
9.61
10.81
11.15
11.22
11.3
Combined Leachate of 2nd Treatment
4 = min 7&8 5 = min 9&10
1 = min 1&2
2 = min 3&4
3 = min 5&6
mL
39
38
36
37
37
EC
2.25
1.11
.78
.57
.45
a-6
JAR 1
JAR 2
JAR 3
CONTROL
SAWDUST
B. juncea
20g Soil, 1 Tablespoon
Vermiculite, 10 ml Water
20g Soil, 1 Tablespoon
Vermiculite, 30 ml Water, 2
Tablespoons Sawdust
20g Soil, 1 Tablespoon
Vermiculite, 15 ml Water, 2g
B. juncea
JAR 4
JAR 5
JAR 6
B. napus
B. Napus (anaerobic)
(NH4)2SO4
20g Soil, 1 Tablespoon
Vermiculite, 15 ml Water, 2g
B. napus
20g Soil, 15 ml Water, 2g B.
napus
20g Soil, 1 Tablespoon
Vermiculite, 15 ml Water,
1.18g (NH4)2SO4
8
a-7
Jar
EXPECTED RESULTS
PostPrePostPreNitrate Nitrate Nitrite Nitrite Pre-pH Post-pH
(mg/l) (mg/l) (mg/l) (mg/l)
N-process
Control
5
20
.3
.15
8.12
6.21
None,
Specifically
Sawdust
5
2
.3
.15
8.12
5.98
Immobilization
B. Napus
5
50
.3
.15
8.12
5.09
Mineralization
B. juncea
5
50
.3
.15
8.12
5.46
Mineralization
Anaerobic
B. juncea
5
0
.3
.15
8.12
7.12
Denitrification
(NH4)2SO4
5
20
.3
.15
8.12
5.68
Nitrification
9