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Effects of Fertilized Biofuel Production on Soil pH
Jiaye Qu
University of Illinois at Urbana-Champaign
Undergraduate Special Problems
Spring 2013
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I. Introduction
The modern lifestyle is completely dependent on the massive consumption of fossil
fuel, from industry, agriculture, transportation to individual households, which
directly leads to the emission of large quantity of CO2 to the atmosphere. During
recent decades, the growing demand of fossil fuel of the developing world as well as
the climatic changes caused by burning fossil fuel makes it more urgent to look for
substitutable energy sources. The first generation biofuels such as corn have many
obstacles that prevent it from being a well-accepted biofuel crop. For example, using
food crops for biofuel production leads to increased food prices and lower availability;
corn leads to large environmental losses of N through nitrate leaching and N2O
emissions (Smith et al., 2013). Thus, the sterile, hybrid grass Miscanthus X giganteus
has been studied as a possible biofuel crop. Miscanthus X giganteus is a rhizomatous
perennial C4 pathway photosynthetic plant that is capable of converting solar energy
to biomass efficiently and using water and nitrogen efficiently (Heaton et al., 2010).
Also, this grass is considered to be resistant to pest and diseases (Maughan et al.,
2012). Miscanthus X giganteus is a cross between Miscanthus sinensis and
Miscanthus sacchariflorus and it was first collected in Japan in the 1930s (Maughan
et al., 2012)
Major worldwide greenhouse gas emissions are carbon dioxide (CO2), methane
(CH4) and nitrous oxide (N2O). The main benefit of using Miscanthus X giganteus as
an alternative biofuel is that it can reduce greenhouse gas emissions (Smith et al.,
2013). Agricultural soils are rich in C and N and the emissions are dependent on crop
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production systems; fertilizer application can promote N2O emissions (Behnke et al.,
2012). According to Behnke’s et al. (2010) results for fertilized Miscanthus in central
Illinois, there was no significant biomass response due to N fertilization, and
moreover, they found that fertilizer additions had greater N2O emissions and
significantly greater total inorganic N leached from surface soils (Behnke et al., 2012).
Applying fertilizers can be important to the establishment period of Miscanthus X
giganteus. However, if the fertilizer increases N2O emissions and inorganic N
leaching from soils, applying fertilizer to the Miscanthus X giganteus may offset its
benefit of reducing greenhouse gas emissions (Behnke et al., 2012). Fertilizers can
also decrease soil pH due to the acidifying nitrification process (Brady and Weil,
2007). The effect of fertilizers as well as the Miscanthus X giganteus production on
soil pH has not been studied. In order to achieve the maximum biomass yield without
degrading the soil, it is important to study the effects of fertilized Miscanthus X
giganteus grass on soil pH. Therefore, the objective of my study is determine the
effect of Miscanthus production on soil pH, with and without the addition of N
fertilizer.
II. Materials and Methods
I utilized soils collected from four field sites in the United States where Miscanthus X
giganteus has been grown since 2008: University of Illinois Urbana-Champaign
(Urbana, IL, 40°06′20″ N, 88°19′18 W), University of Kentucky (Lexington, KY,
38°07′45″ N, 84°30′08 W), University of Nebraska-Lincoln (Mead, NE, 41°10′07″ N,
96°28′10″ W), and Rutgers, The State University of New Jersey (Adelphia, NJ,
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40°13′31″ N, 74°14′54 W). Soil samples were collected in 2008 from each of these
sites at 0–10, 10–20, 20–30, 30–50, and 50–100 cm depths (Maughan et al., 2012)
before Miscanthus was planted. The soil pH, texture, CEC and % SOM were
measured and reported by Maughan et al. (2012); these soil pH values can be used as
control in my study. At each location plots were arranged in a randomized complete
block design with four replicates. Three N treatments (0, 60, and 120 kg ha-1
) have
been used beginning with the establishment year (2008). Soil core samples were
collected again from each plot from 0-10 and 10-30 cm depths during March of 2012,
following 4 years of Miscanthus growth. I will measure soil pH on the 0-10 cm soil
samples from 2012 to determine if pH has changed in response to Miscanthus growth
and/or fertilization.
III. Analytical Procedure
Soil samples from 2008 and 2012 were sorted by site, amount of nitrogen fertilizer
applied, and year. There were four replications. 2.50 g of each soil sample was
weighed in small beakers with a tolerable range of error 2.50 g ~ 2.55 g. After
weighing each soil sample, 25 mL of DDW was added to each beaker to mix with the
soil samples. The soil solution mixture was then stirred for 10 seconds with a stirring
rod at 0, 15, 30, 45, and 60 minutes, respectively, after addition of DDW. Then, the
suspension was allowed to settle for 30 minutes. Finally, the pH electrode was placed
in the suspension with the ceramic junction immersed just deep enough into the clear
supernatant solution to establish good electrical contact. The electrode did not touch
the beaker. Readings were recorded to nearest 0.01 pH unit after 30 seconds. Properly
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functioning pH electrodes should produce stable readings with 30 seconds. A second
reading was recorded after 2 minutes. Readings at 30 seconds and 2 minutes did not
differ by more than +/- 0.05 pH. The effect of Miscanthus production was evaluated
using a paired t-test in SAS to compare 2008 pH values by site with 2012 values.
Response to fertilization was evaluated using the GLM procedure in SAS for 2012
samples.
IV. Results
The mean soil pH by N fertilizer treatment (0, 60, and 120 kg N ha-1
) for each site
showed no significant difference (Figure 1). For the KY and NE site, the average soil
pH increases with increasing amount of N fertilizers applied, although not
significantly (p > 0.05). However, the average soil pH is inversely related to the
amount of N fertilizers treated in NJ and VA sites. There was no pattern shown for the
IL site. The trends noticed in KY, NE, NJ and VA sites are too weak to show
significant response (p > 0.05), with a maximum pH difference of 0.38. Also, the
trends in KY and NE are the opposite of those in NJ and VA. (N fertilizers made soil
slightly more basic in KY and NE but more acidic in NJ and VA.)
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Figure 1. Mean soil pH by N fertilizer treatment (0, 60, and 120 kg ha-1
) at each
of the study sites using 2012 samples.
Using a paired t-test to evaluate the response of soil pH at the five sites between
2008 and 2012, the results showed that the means of pH values in different states did
not change much from 2008 to 2012 except for Kentucky, before and after
Miscanthus was planted. (Figure 2). The soil pH changes of IL, NE, NJ are not
significant (P-value > 0.05). The mean soil pH of Kentucky increased significantly (p
< 0.05) from 5.11 to 5.44, which is the opposite of what I expected - planting
Miscanthus makes the soil more acidic.
0
1
2
3
4
5
6
7
IL KY NE NJ VA
0 kg ha-1
60 kg ha-1
120 kg ha-1
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Figure 2. Mean soil pH by state in 2008 and 2012 for sites planted in
Miscanthus.
V. Discussion
There is no obvious yield response of Miscanthus X giganteus to the application
of N fertilizers (Maughan et al., 2012), but fertilizers can be important to the
establishment period of Miscanthus X giganteus. The results of my experiment
contradict the hypothesis that applying N fertilizer can decrease soil pH due to
acidifying nitrification process. Therefore, applying fertilizers to Miscanthus X
giganteus during the establishment period is likely to be viable. Also, planting
Miscanthus X giganteus did not significantly alter the soil pH of the sites. The
unchanged soil pH might be contributed by an advantage of Miscanthus X giganteus;
past experiments also show that corn-soybean had a mean pH significantly less than
Miscanthus and switchgrass (Davis et al., 2013). One exception of the general pattern
of Miscanthus X giganteus's effect on soil pH is the Kentucky site. It is possible that
0
1
2
3
4
5
6
7
IL *KY NE NJ VA
2008 pH
2012 pH
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Kentucky soil is exceptionally sensitive to Miscanthus X giganteus because soils in
different state have different properties. The reason why Miscanthus X giganteus only
significantly increased the soil pH in Kentucky (not in any other states) is still yet to
be determined.
However, the result of one experiment may not be sufficient enough to draw the
conclusion that applying nitrogen fertilizer to Miscanthus X giganteus does not have
an effect on soil pH. The limitation of the experiment is that the range of treatment is
only 0 to 120 kg ha-1
, which only shows that applying nitrogen fertilizers of less than
120 kg ha-1
does not have a significant effect on soil pH. If we increase the fertilizer
treatment to more than 120 kg ha-1
, the results of the experiment could possibly be
different. Also, this study was conducted after 4 years of Miscanthus production.
Perhaps during a longer treatment period there may be a response in soil pH.
VI. Conclusion
Miscanthus X giganteus is a biofuel crop that has benefits of high water use
efficiency, low nitrogen fertilizer requirement, etc. However, young Miscanthus X
giganteus still need nitrogen fertilizer for establishment. This research focuses on how
Miscanthus X giganteus can affect soil pH and whether applying nitrogen fertilizer to
Miscanthus X giganteus can change the soil pH. The results of the study show no
significant correlation between application of nitrogen fertilizer and soil pH. Also,
there is no significant soil pH change from 2008 to 2012, before and after Miscanthus
X giganteus was planted. Although this research did not find any effect of Miscanthus
X giganteus on soil pH, it does not mean planting Miscanthus X giganteus will never
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degrade the soil or cause any ecological problems. Using Miscanthus X giganteus as a
biofuel crop requires more agricultural land to grow Miscanthus X giganteus. pH is an
important indicator of soil quality. The sustainability of using Miscanthus X giganteus
as a biofuel crop is largely based on Miscanthus X giganteus's effects on soil pH and
the overall soil quality.
References:
Behnke, G.D., M.B. David, and T.B. Voigt. 2012. Greenhouse gas emissions, nitrate
leaching, and biomass yields from production of Miscanthus x giganteus in
Illinois, USA. BioEnergy Research 5:801-813.
Brady, N.C. and R.R. Weil. 2007. The Nature and Properties of Soils, 14th
edition.
Prentice-Hall.
Davis, M.P., M.B. David, and C.A. Mitchell. 2013. Nitrogen mineralization in soils
used for biofuel crops. Communications in Soil Science and Plant Analysis
44:987-995.
Heaton, E.A., F.G. Dohleman, A.F. Miguez, J.A. Juvik, V. Lozovaya, J. Widholm,
O.A. Zabotina, G.F. McIsaac, M.B. David, T.B. Voigt, N.N. Boersma, and S.P.
Long. 2010. Miscanthus: a promising biomass crop. Advances in Botanical
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Maughan, M., G. Bollero, D.K. Lee, R. Darmody, S. Bonos, L. Cortese, J. Murphy, R.
Gaussoin, M. Sousek, D. Williams, L. Williams, F. Miguez, and T. Voigt. 2012.
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Smith, C.M., M.B. David, C.A. Mitchell, M.D. Masters, K.J. Anderson-Teixeira, C.J.
Bernacchi, and E.H. DeLucia. 2013. Reduced nitrogen losses following
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