Biology IBH1
Design Laboratory
Manuele Cavalli-Sforza
02/03/10
Investigating the relationship between soil salinity and growth in two Philippine rice (Oryza
sativa L.) varieties: Dinorado and IR-841.
Research Question: What is the relationship between the salinity of the soil and the change in the dry
mass of rice (Oryza sativa L.) seedlings in the two different varieties, Dinorado and IR-841, when grown
to mature grain stage?
Background information: Soil salinity has a significant effect on rice yields by several mechanisms and
consequently poses a major obstacle to rice production worldwide1. Although other crops have
exhibited inhibition that is specific to the proportion of soil ions, osmotic pressure has been shown to be
the most significant factor regarding salinity to affect the dry mass of rice at the mature grain stage2.
Although rice exhibits anion specific inhibition by chlorine at the flowering stage2, the mature-grain
stage ultimately determines yields, and therefore will be the stage of growth investigated. All yield
related characteristics, such as fertility, till length, panicle number and panicle length are affected by soil
salinity3. This study will investigate the effect of salinity on the final yield of one plant cycle by measuring
the dry mass of the mature grains.
Other factors affecting photosynthetic rate and plant growth must also be considered. The intensity and
color composition of the light received by the growing rice, for instance. Different plant varieties have
different action spectra and therefore will perform better at different wave lengths4. External
temperature and root temperature also affect rice growth. External air temperature could affect the
rate of enzymatic reactions in the plant, such as the fixation of CO2 by RuBP carboxylase in the Calvin
cycle5, whereas root temperature affects rice growth by influencing root porosity and therefore nutrient
intake5. Soil composition, including the availability and proportion NPK compounds, humus deposits, the
microbiological composition of the soil6, moisture tensions, oxygen7 and carbon dioxide5 levels all affect
rice growth by affecting physiology and levels of limiting factors in key metabolic reactions.
Hypotheses: As the salinity of the solutions used to irrigate Oryza sativa L. increases, the plants from
both varieties will decrease because of the effect of the solutions’ decreased osmotic pressure. A
decreased osmotic pressure limit of solutions surrounding plant roots suppresses the plant’s
transpiration stream and therefore limits its ability to transport minerals and NPK compounds from the
roots to the rest of the plant. When irrigation solutions become hypotonic, the dry mass of the plants
may no longer be able to grow past a certain stage of germination because the transpiration stream will
be so significantly interrupted.
1
Zheng, Linghe, and Michael C. Shannon. "Salinity Effects on Seedling Growth and Yield Components of Rice." Crop
Science 40 (2000): 996-1003. CropScienceJournal.org. Crop Science Society of America. Web. Feb. 2010.
<http://crop.scijournals.org/cgi/content/full/40/4/996>.
2
Ehrler, William. "Some Effects of Salinity on Rice." Botanical Gazzette 122.2 (1960): 102-04. JSTOR. Web. Feb. 2010.
<http://www.jstor.org/pss/2473354>.
3 Shereen, Aisha, S. Mumataz, S. Raza, M. A. Khan, and S. Solangi. "Salinity Effect on Seedling Growth and Yield
Components of Different Inbred Rice Lines." Pakistani Botanical Journal 37.1 (2005): 131-39. Print.
4 Allott, Andrew. IB Diploma Programme Biology Course Companion. New York: Oxford UP, USA, 2007. Print.
5 Setter, T. L., and H. Greenway. "Growth Reductions of Rice at Low Root Temperature: Decreases in Nutrient Uptake and
Development of Chlorosis." Oxford Journal of Experimental Botany 39 (1998): 811-29. Oxford University Press. Web. Feb.
2010. <http://jxb.oxfordjournals.org/cgi/content/abstract/39/6/811?ck=nck>.
6 Studies on nutrient uptake of rice and characteristics of soil microorganisms in a long-term fertilization experiments for
irrigated rice." Journal of Zhejiang University Science 6.2 (2005): 147-54. PubMed. Web.
<http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1389631/>.
7 Patrick, W., and W. Fontenot. "Growth and Mineral Composition of Rice at Various Soil Moisture Tensions and Oxygen
Levels." Agronomy Journal 68 (1976): 325-29. Web. Feb. 2010.<http://agron.scijournals.org/cgi/content/
abstract/68/2/325>.
1
Independent Variable: Concentration of saline solution (± 0.05 𝑀) added to soil sample every two
days. Five levels of treatment will be used: 0.00 M, 0.25 M, 0.50 M, 0.75 M and 1.00 M.
Dependent Variable: The dry mass of the each seedling per level of treatment (±0.01𝑔) after growing
for 12 weeks irrigated in saline solution.
Table 1: Controlled variables and methods for controlling and monitoring them.
Variable
Method to control
Method to monitor
Light Intensity
and Color
Composition
Trays will be placed in the same areas of the High School
courtyard and will therefore receive the same fluctuations of
light composition and intensity.
One data logging probe light intensity
sensor to be placed beside each tray.
Temperature
of roots and
external air:
All trays will be kept at ground level in the same 2 X 2 m space.
Therefore, variations in external air temperature should be
negligible between trays. Consequently, root temperatures
should be negligibly different as the soil is the same volume and
depth in each tray and each tray is made of the same material
and therefore will have the same insulating properties.
Soil
composition:
In order to control for soil composition and moisture, 32 kg of
soil will be ordered from the same supplier. The soil will then be
heated 250oC in an oven for 10 minutes in batches of 3.2 kg in
order to sterilize the soil, neutralizing the effect of varied
densities of microbiological fauna and moisture content. Dry,
powdered soil is also much easier to tumble and facilitates the
mixing of soil particles to improve the homogeneousness of the
distribution of nitrogen, phosphorus and potassium (NPK)
compounds. The soil will be removed and any clumps crushed
so that it can be more effectively homogenised when turned in
a tumbler for 5 minutes.
The tray will be flooded to 1 cm above the soil level.
A pilot study will be conducted by placing a tray of the same
dimensions with 1 cm of water out in the High School courtyard
from 5.00 am-6.00 pm and measuring the change in water
level. Therefore estimations of the volume of distilled water
and mass of salt necessary for the experiment will depend of
the results of this study.
In order to control for genetic variation among seedlings, or
other factors predisposing seedlings to unusually low or high
levels of growth, seeds will be grown for 5 days. Soil will be
prepared as described in the procedure to control soil
composition and irrigated, according to the procedure to
control soil humidity, with tap water from a single source. Five
seedlings that fall within
1cm of the modal height of all
seedlings grown will be selected for each level of treatment.
Any seedlings with unusually light or dark leaf coloration will be
excluded from this selection.
Seeds will be evenly spaced as illustrated in figure 1 and
seedlings spaced as illustrated in figure 2 in order to ensure
maximal and evenly distributed space for the root growth of
each seedling and plant.
One data logging temperature probe in
each tray; as the external air temperature
and the root temperature are closely
linked when the rice is planted in each
tray no temperature probes will be used
to measure external air temperature over
each tray due to the availability of the
equipment at school.
The concentration of NPK nutrients will
be evaluated using the LaMotte NPK Soil
Test Kit©.
Soil humidity:
Seedling
health:
Seedling
distributions:
2
Every day the water level will be
measured at 6.00 pm (close to sunset)
with a ruler, and the tray will be flooded
to 1 cm above the soil level.
-
-
Diagrams:
Figure 1: Arrangement of seeds in seed bed.
Figure 2: Arrangement of selected seedlings
20 cm
20 cm
9.42 cm
Rice seed
9.42 cm
20 cm
20 cm
9.42 cm
9.42 cm
9.42 cm
6.67 cm
Figure 3: Bird’s eye view of tray arrangement in centre of HS courtyard.
Key:
= 30 cm
= Oryza sativa L. Dinorado
= Oryza sativa L. IR-841
0.00M
0.25M
0.50M
0.75M
1.00M
0.25M
= Concentration of saline solution used.
= Opaque 1 X 1 m table covering laptop.
0.00M
nsh
0.25M
0.50M
0.75M
1.00M
= Temperature probe connected to laptop
via HUB.
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1)
2)
3)
4)
5)
6)
Materials:
32 kilograms of soil.
1.8 kilograms of NaCl.
26 litres of water (in container)
45 Dinorado and 45 IR-841 seeds.
Apparatus:
Ten 20 X 20 X 8 cm trays.
Five 20 X 20 X 8 cm steel oven trays.
One LaMotte NPK Soil Test Kit©.
One oven with gas tank and
thermostat.
 One mortar and pestle.
 20 data logging temperature probes
and appropriate HUB hardware to
 One 5 kilogram soil tumbler – modify
connect 10 probes to one computer.
a raffle ticket tumbler if necessary.
 Two spades.
 One soil sack.
 One digital weighing scale.
 Ten 100cm3 beakers.
 One stirring rod.
 One spatula.
 Two opaque 1 X 1 m table.
 Two laptops with data logging
software.
Procedures:
Measure the weight of the soil and steel tray before baking.
Oven-bake the 32 kg of soil in 10 batches of 3.2 kg at 250oC for 10 minutes to sterilize soil and
standardise moisture content by evaporating water in soil.
Measure the percentage weight lost by the evaporation of water. Calculate the resulting mass of dry soil
that should be apportioned to each tray.
As each batch is removed crush soil clumps with pestle (and mortar if necessary) to help soil reach a
powdery consistency (see table 1 for reasons).
Tumble the soil continuously for 5 minutes in 5 kilogram batches. After each batch leave approximately
half of the soil in the tumbler before adding as much newly dried soil to the tumbler as mixed soil taken
out this is to help ensure that the soil is homogenized across the batches, not simply within each batch.
As soil is mixed and taken out of the tumbler add the mass of soil calculated in step 3 to each tray.
3
7) Take 0.1g samples, composed of smaller samples from different 5 places on the topsoil (each of which is
at least 2 cm apart), from each tray and use the LaMotte NPK Soil Test Kit© to qualitatively evaluate the
concentration of NPK compounds
8) Use a ruler to ensure that the soil is evenly distributed across the bottom of the container.
9) After the soil is distributed to each container, even out the soil such that the height of the soil in each
container falls within ±0.5 cm (across the surface of the container) of the mean height of the soil in
each container.
10) Distribute the seedlings as indicated in figure 1, placing each seed 0.5 cm below the surface, covering it
back up with the displaced soil.
11) After step has been carried out for each tray, slowly flood each tray until the water level lies 1 cm above
the soil line, attempting not to excessively disturb the top soil.
12) After step 10 has been carried out for each tray, assemble the trays and connect the data logging
apparatus as indicated in figure 3, away from the shade of the trees.
13) Water the trays every day, for 5 days, as indicated in the procedure to control soil humidity (table 1).
14) During these five days, prepare 1000 cm3 of each saline solution (0.00M, 0.25M, 0.50M, 0.75M, and
1.00M).
15) After 5 days, select seedlings by the procedure outlined to control seedling health (table 1).
16) Replant the 5 selected seedlings from each level of treatment as indicated by figure 2.
17) Water the trays, with the saline solutions prepared in step 14, as indicated in the procedure to control
soil-humidity (table 1). Prepare approximately 800cm3 of each saline solution each succeeding week
according to the amount necessary to water each tray by the protocol to control soil humidity (table 1).
18) At the end of 12 weeks, remove each of the 5 rice plants from each level of analysis and bake them
evenly spaced in a steel cupcake rack, one plant per cup cake division, at 150oC for 20 minutes.
19) Tare a 100cm3 beaker on the digital weighing scale and carefully transfer the dried mass of the one rice
place the beaker. Record the data in the tables below and repeat this step for the remaining rice plants.
4
Table 2: The relationship between the concentration of saline solution added to soil ( 0.05M) and the
dry mass of the Oryza sativa L. Dinorado plant (±0.01g) after it is grown for 12 weeks.
Concentration of saline solution
used to flood crop (+/- 0.05M)
0.00
0.25
0.50
0.75
1.00
Plant
number
1
2
3
4
5
1
2
3
4
5
5
2
3
4
5
1
2
3
4
5
1
2
3
4
5
Dry mass of Oryza sativa L. IR-841
plant (+/- 0.01g)
Average dry mass of Oryza sativa L.
IR-841 plant (+/- 0.01g)
Standard
Deviation
Table 3: The relationship between the concentration of saline solution added to soil ( 0.05M) and the
dry mass of the Oryza sativa L. IR-841 plant (±0.01g) after it is grown for 12 weeks.
Concentration of saline solution
used to flood crop (+/- 0.05M)
0.00
0.25
0.50
0.75
1.00
Plant
number
1
2
3
4
5
1
2
3
4
5
5
2
3
4
5
1
2
3
4
5
1
2
3
4
5
Dry mass of Oryza sativa L. IR-841 plant
(+/- 0.01g)
5
Average dry mass of Oryza
sativa L. IR-841 plant (+/- 0.01g)
Standard
Deviation
6