IJERD – International Journal of Environmental and Rural Development (2016) 7-1

Research article
erd

Carbon Dioxide Release as an Index of Mineralization Rates ofOrganic Substrates
SAMBO PHEAP*
Royal University of Agriculture, Phnom Penh, Cambodia
Email: psambo@rua.edu.kh, ph.sambo@gmail.com

GINA V. PANGGA
Agricultural Systems Cluster, College of Agriculture, University of the Philippines, Los Baños,
Laguna, 4013, Philippines

JOCELYN D. LABIOSAgricultural Systems Cluster, College of Agriculture, University of the Philippines, Los Baños,
Laguna, 4013, Philippines

EVALOUR T. ASPURIA
Crop Science Cluster, College of Agriculture, University of the Philippines, Los Baños, Laguna,4013, Philippines
Received 15 November 2015

Accepted 11 April 2016(*Corresponding Author)

Abstract Mineralization of nutrients from organic materials is vital for optimum plant growthand development. Various methods have been used to evaluate the mineralization rate ofdifferent organic substrates. Of these, carbon dioxide release is a reliable method to estimate
mineralization rate. Four different substrates: dry chicken manure, Azolla, coconut coir dust(CCD), and Gliricidia sepium leaves and the combination of these substrates with SNAP
solution on their rates of mineralization was determined. The results were significantly different
in the amounts of CO2 released from the substrates. CO2 release from the substrates wasstimulated by SNAP. Among all treatments, G. sepium with SNAP yielded the highest amountwhile coconut coir dust gave the lowest. Nitrogen mineralized to about fifty percent (50%)
during the first week of all treatments. Using soil organic materials such as G. sepium leaves
would quickly provide the soil with more mineralized nutrients which are available for plant
growth and development.
Keywords mineralization, CO2 release, organic substrates, Gliricidia sepium

INTRODUCTION
Mineralization is an important process which regulates the nutrient cycle (Curtin et al., 1997). It is alsoa continuous process which is controlled by many factors such as temperature (Curtin et al., 1997;Crohn, 2004; Gaskel and Smith, 2007; Li and Li, 2014), moisture (Curtin et al., 1997; Gaskel andSmith, 2007), pH (Curtin et al., 1997; Ouyang et al., 2008), microorganisms (Frankel and Bazylinski,2003; Allison et al., 2009) or organisms of higher class such as earthworms (Coúteaux et al., 1995),
herbivores (Schrama et al., 2013), soil properties such as clay types (Deenik, 2006), substrate qualityand quantity (Howard and Howard, 1993; Eiland et al., 2001; Gaskell and Smith 2007; Li and Li,2014), and the cultivation practices.
Understanding the processes involved in mineralization, and the factors that affect mineralization
rate, would help estimate the right type and amount of mineralized material to guarantee optimum yieldⒸ ISERD124

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and minimize the adverse effects of the over application of nitrogen (N) sources (Pereira et al., 2006;Hartz et al., 2000; Crohon 2004; Bordilio et al., 2013; Li and Li, 2014).
The contents of carbon dioxide (CO2) determine the rate of mineralization by measuring thetrapped CO2 in the alkali solution, such as Ca(OH)2, NaOH or KOH and titrate it against hydrochloric
acid (HCl) with addition of barium chloride (BaCl2) (Peirera et al., 2006; Hartz and Britton, 2003;
Makende and Ayeni, 2013).
OBJECTIVE
The objectives of this study were to estimate the mineralization rates of different organic materials
using the CO2 release as an index, and to examine the effects of nutrient additions on themineralization rates of these materials.
METHODOLOGY
Soil samples (Alipit Clay Soil) were collected from an unfertilized upland area of the U.P. Los Baños
Central Experiment Station. The soil was air-dried, cleaned from vegetative material and passed
through a 2.0 mm sieve. Fifty (50) grams of this sieved soil was placed inside incubation jars andmixed with 0.125 g of each nutrient source (5 t ha-1). Complete Randomized Design (CRD) with three
replications was used in this experiment. The treatments were: Control (CT)-soil alone with noadditional nutrients, dry chicken manure (CM), coconut coir dust (CCD), Gliricidia sepium (GS),Azolla (AZ), simple nutrient addition program (SNAP) nutrient solution, CM + SNAP, CCD + SNAP,
GS +SNAP and AZ + SNAP. The incubation study was conducted from April to May 2014 in the SoilFertility Laboratory of the Agricultural Science Cluster (ASC), College of Agriculture, U. P. LosBaños, Philippines.
The Simple Nutrient Addition Program (SNAP) nutrient solution was formulated by the Instituteof Plant Breeding, College of Agriculture, U.P. Los Baños. The solution was prepared by combining
20 ml of SNAP A and 20 ml of SNAP B, and adding this to one liter of distilled water. Forty (40) ml of
the prepared SNAP solution mixture was added to each SNAP-treated jar.
Determination of Carbon Dioxide Release and Mineralized Nitrogen
Mineralization rate was measured by determining the amount of CO2 released from the differenttreatments. The incubation jar set-up was prepared prior to the start of the experiment. Prior toapplication, the substrates were grounded and oven-dried overnight at 40qC. The appropriate amount ofresidue was added to 50 g soil at a rate of 0.125 g jar-1. Based on the amount of soil, this application
rate approximates to 5 t ha-1, the amount of residue applied in many farming systems. For the controltreatment, no organic material was added in the same amount of soil. The experiment was conducted
for the duration of approximately 8 weeks.
The mixtures of soil and treatment nutrient sources were supplied with moisture at field capacity.
A 50 mL beaker containing 30 mL of 0.3 M NaOH was placed in the center of the jar to trap the CO2
released from each treatment. The trapped CO2 was then transferred to a 100 mL beaker, and 3 drops ofphenolphthalein were added before titration with 0.2 M HCl.
RESULTS AND DISCUSSION
The incubation experiment examined the mineralization rate of different organic materials over a 7-day
period. Results showed that there were significant differences between treatments. The highest amountⒸ ISERD

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IJERD – International Journal of Environmental and Rural Development (2016) 7-1of CO2 released on the first day was measured from Azolla and AZ + SNAP with 78.3 and 76.6 mg kg-1
soil, respectively. These treatments were closely followed by G. sepium and CM + SNAP with 72.3and 70.9 mg kg-1 soil respectively. Since the measured CO2 from these four treatments were ranked
closely, differences of the CO2 released were found to be insignificant.
The measured CO2 on the second day showed that soft, fresh materials with high source of N
continuously exhibited faster rate of mineralization when compared with other organic materials.
Treatments with Azolla and G. sepium demonstrated the highest amount of CO2 with 74.2 and 72.7 mg
kg-1 soil, respectively. The addition of nutrients hastened the mineralization rates as shown by Azolla +SNAP and GS+ SNAP. Similar effects were observed from Day 3 to Day 7 as those treatments withSNAP recorded high amount of CO2 release. The G. sepium + SNAP Treatment dominated othertreatments and their differences were found to be significant. Its performance is clearly presented inFig. 1. Treatments with Azolla and G. sepium alone ranked second and third. It is also interesting tonote that coconut coir dust played second on Day 3 to 4. Fontaine et al. (2003) reported that theincrease in the amount of CO2 released in the first week for all treatments may be attributed to theactivities of microorganisms attacking the labile and readily decomposable substrates such as sugar,starch, and cellulose. The surge of CO2 released from the soil in the first day (Fig. 1) might due torewetting of the soil which allowed the surviving microorganisms to immediately attack SOM and thesubstrates (Keift et al., 1987). The control, although having a lower total CO2 release, it had a starting
point which was also as high as chicken manure and SNAP solution. The soil had high SOM content(6.3%) could increase mineralization.
CO2 evolution (mg kg-1)

100806040200123Time (Day) 4Control
Azolla (AZ)
Gliricidia sepium (GS)CM + SNAP

567Dry Chicken Manure (CM)
Coconut Coir Dust (CCD)
SNAP solution (SNAP)AZ + SNAP

Fig. 1 Daily carbon dioxide (mg kg-1) released from different organic substrates
over the period of seven days
Franzluebbers et al. (1994) concluded that N mineralization can be related to the amount of SOM
in the soil. Another study of Chuwdhury et al. (2014) on the effect of malic acid addition to CO2
release found that treatments with or without nutrient addition had very high CO 2 production from 20
to 40 hours after incubation. According to Chen at al. (2014), fresh materials have faster mineralization
rates and release more CO2. G. sepium treatment was observed with consistent high amounts of CO2
released, followed by Azolla and chicken manure.

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Haney et al. (2008) also found a strong relationship between organic carbon sources and CO2
release in the first day of incubation. In their study on the effect of drying and rewetting, the greatest
CO2 respiration lasted for three days. The reason which led to this highest rate of CO2 release might bedue to the active microbial biomass breaking it down when they were exposed to dryness.
The incubation experiment also examined the mineralization rate of different organic materials overan 8-week period. The results showed that there were significant differences between treatments. The
highest amount of CO2 released in the first week was measured from G. sepium + RR with 375.13 mg kg1
soil. It was followed by Azolla and GS with 312.84 and 312.40 mg kg-1 soil, respectively. Notably,
their values are almost equal. Azola + SNAP and CM + SNAP rank next with 299.72 and 288.14 mg kg1
soil, respectively. There is a significant difference of the amount of CO2 released from G. sepium
compared the succeeding treatments ranked. In a similar study, Pangga et al. (2000) observed that morethan 50% of total C has released during the first week of incubation.
A sharp decline in the amounts of CO2 released was observed in Week 2. The highest amount ofCO2 released during this week was from CM and GS + RR, both yielding 93.28 mg kg-1 soil. This wasfollowed by Azola and CM + RR with close values of 83.60 and 80.96 mg kg-1 soil, respectively.
Differences of the CO2 released among treatments were found to be insignificant since the measured CO2
from these four treatments were ranked closely, From Week 2 to Week 6, CM and GS + RR recordedhigh amounts of CO2 released compared to the other treatments. However, the highest amount of CO2released during Week 7 a nd 8 was measured from G. sepium.
CO2 evolution (mg kg-1)
400350300
25020015010050012345678Time (week)
ControlAzolla (AZ)
Gliricidia sepium (GS)CM + RR
CCD + RR

Dry Chicken Manure (CM)
Coconut Coir Dust (CCD)
SNAP solution (SNAP)AZ + RR
GS + RR

Fig. 2 Weekly carbon dioxide (mg kg-1) released over the period of eight weeks
from different substrates and with the addition of SNAP solution
Throughout the succession of weeks, the amounts of CO2 lowered, although several peaks occurred,
yet they were lower after each time. In the third week, there was an increased observation in CM+ SNAP
treatment which measured 80.96 to 100.03 mg kg-1. Then there was another peak in AZ+ SNAP (60.72 to65.41 mg kg-1). On the seventh week, there were three rises of CO2 in GS, AZ and SNAP treatments(45.17 to 58.66, 38.72 to 55.78 and 41.65 to 45.32 mg kg-1, respectively). Makinde and Ayeni, (2013)
also observed several peaks of CO2 release in their study. The decomposition of OM can be dividedinto three stages—(i) active (1-6 weeks), (ii) reduced or slow (7-8 weeks) and (iii) stable or moderatelyⒸ ISERD127

IJERD – International Journal of Environmental and Rural Development (2016) 7-1stable (9-16 weeks) (Ayeni, 2011). In the active stage, the most readily available and easily
decomposed substrates and OM will be decomposed. At the same time, microorganism populations
also increase quickly. When substrate quality was reduced, microorganism population becomes stableor dead and decomposed to serve as the nutrient source for other microorganisms and plants.
Cumulative CO2 release also showed that addition of substrates increased the amount of CO2 ascompared with the treatments with substrates only (Figs. 1 and 2). Fresh materials have fastermineralization rates (Chen at al., 2014), especially G. sepium which consistent high amounts of CO2
released was observed, followed by Azolla and chicken manure. Additional nutrient sources will
increase CO2 and CH4 production (Gogo and Pearce, 2009). Generally low-quality soil carbon limits
microorganism activities as well as carbon mineralization. When additional nutrient sources are added
to the soil, microorganisms will attack these sources and rapidly increase their population (Fontaine etal., 2003).
CONCLUSION
Mineralization of organic materials was about fifty percent (50%) in all substrates as compared to theamount of carbon dioxide released during the first week. The highest total CO2 released was produced
during the first week and the peak was between the first two days. The amount of CO 2 released lessand less through time as the quality of the substrates eventually decreased. Using additional nutrient
source (SNAP) to all organic materials resulted in faster rates of mineralization. Overall, the GS +SNAP treatment has the fastest rate of CO2 release.
ACKNOWLEDGEMENTS
The authors extend the gratitude and appreciation to the Southeast Asian Regional Center for Graduate
Study and Research in Agriculture (SEARCA), Philippines, for granting scholarship in this study; andRoyal University of Agriculture (RUA) for the opportunity and providing valuable assistance in thecompletion of the study.
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