IJERD – International Journal of Environmental and Rural Development (2023) 14-1

Research article
erd

Research article
Conditions of Bio-Slurry Application in Crop Production
inKampong Cham Province, Cambodia

CHAN MAKARA MEAN*
Faculty of Agricultural Engineering / Faculty of Agronomy,
Royal University of Agriculture, Phnom Penh, Cambodia
Email: meanmakara321@gmail.com

LYHOUR HIN
Faculty of Agricultural Engineering, Royal University of Agriculture, Phnom Penh, Cambodia

SOPHOANRITH RO
Faculty of Agronomy, Royal University of Agriculture, Phnom Penh, Cambodia

NARETH NUT
Faculty of Agricultural Engineering, Royal University of Agriculture, Phnom Penh, Cambodia

NAM SOK
Faculty of Agricultural Engineering, Royal University of Agriculture, Phnom Penh, Cambodia

LYTOUR LOR
Faculty of Agricultural Engineering, Royal University of Agriculture, Phnom Penh, Cambodia

BART FREDERIKS
Independent Bioenergy Consultant / Biogas Technology and Information Center,
Royal University of Agriculture, Cambodia
Received 16 January 2023

Accepted 10 May 2023(*Corresponding Author)

Abstract Bio-slurry is an organic fertilizer produced from the decomposition of organic wasteor residues in anaerobic digestion. It is applicable for improving vegetable production as it
contains necessary nutrients such as nitrogen (N), phosphorus (P), and potassium (K) for plant
growth and organic matter that improves soil structure and water-holding capacity. About
29,000 biodigesters have been installed across Cambodia using animal waste to produce
biogas, so huge quantities of bio-slurry are produced. Therefore, this study aimed (1) to assess
the conditions of bio-slurry application in crop production in rural areas, (2) to determine NPK
content in the bio-slurry, and (3) to estimate annual bio-slurry production and NPK production
from biodigesters. The research was conducted between April and September 2022 byselecting 30 farming households that have biodigesters and use bio-slurry for crop cultivationin Prey Chhor District, Kampong Cham Province. It was found that 70% of the farmers usedbio-slurry for rice cultivation and 16.7% for backyard vegetables, basically before planting.
The nutrient content of slurry produced from cow manure consists of 0.20% N, 0.22% P, and
0.44% K. Most farmers preferred to use solid slurry for rice cultivation and liquid slurry forvegetables such as chili peppers, sweet peppers, eggplant, spinach, mustard greens, andcucumbers. However, bio-slurry was commonly mixed with chemical fertilizer in the crop
growth stage. Farmers are willing to use both slurry and chemical fertilizers as this helps theplants to grow well and have higher yields.
Keywords bio-slurry, biodigesters, crop production, vegetables, chemical fertilizer

INTRODUCTIONⒸ ISERD

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The installation of biodigesters has increased in rural Cambodia due to the need to help small-holder
farmers manage animal waste and convert it into energy for cooking and other applications in theirlivelihoods. They also utilize bio-slurry, a by-product produced from biogas production, as organic
fertilizer for crops. According to a 2019 assessment report released by the National Biodigester
Program (NBP), almost 29,000 digesters have been constructed across Cambodia in the period 20062012. Farmers normally raise cattle and use animal manure as a substrate for the biodigesters, andapply slurry, sometimes mixed with compost or other organic fertilizer, to their backyard vegetablegarden and rice cultivation (Hyman and Bailis, 2018). In 2020 alone, of the planned 1,500
biodigesters, 703 were constructed, which was equivalent to 47% (NBP, 2019). Among all theinstalled biodigesters, it is reported that there are approx. 2,353 digesters used by small-holder
farmers in Kampong Cham Province, which is well-known for agricultural production on a large
landscape. Among all the districts in this province, Prey Chhor, Choeung Prey, and Kong Meas had
the highest number of biodigester installations compared to others (PDAFF, 2021).
In Cambodia, vegetable production was reported to be approx. 716,000 tones in 2020, eventhough this country experienced covid-19 pandemic and strict lockdowns. Yet, it was seen as a great
opportunity for the agricultural sector to increase local production by reducing dependency on
agricultural imports from the neighboring countries. Until now, it is also noticed that chemicalfertilizer has still been in high demand, as farmers consume it in their crop production whencompared to organic fertilizer in the form of compost or bio-slurry (Phnom Penh Post News, 2021).
Technically, bio-slurry is considered one of the most efficient organic fertilizers, when applied tocrops, since it is produced through anaerobic digestion. Therefore, it can be used instead of chemicalfertilizer in every stage of crop growth. Furthermore, slurry also helps increase crop yield by 30%,
when compared to chemical fertilizer, which leads to a reduction in production costs of 50% (Hymanand Bailis, 2018). One study showed that a 25 m3 digester can produce 9,780 kg of bio-slurry
annually, consisting of 76 kg of nitrogen (N), 107 kg of phosphorus (P), and 107 kg of potassium(K), respectively (Kissan, 2019). That finding also indicated that bio-slurry contains 93 % water and
7% dry matter of which 4.7% was organic matter and 2.5% was inorganic matter (Kumar et al., 2015).
In addition, the utilization of bio-slurry was efficient in accelerating crop growth and increasing
vegetable yield in both seasons. Aina (2018) illustrated that 50% bio-slurry mixed with 50% chemicalfertilizer was more efficient than 100% of chemical fertilizer in promoting crop growth and yieldbecause the bio-slurry had only high N content, whereas other nutrients were obtained from chemicalfertilizer.
Bio-slurry can be a major solution for farmers who intend to use organic fertilizer to improvetheir crop production, and this comes at the right time due to the increase of biodigesters in ruralareas.
OBJECTIVE
This study aimed to (1) to assess the conditions of bio-slurry application in crop production in rural
areas, (2) to determine NPK content in the bio-slurry, and (3) to estimate annual bio-slurry production
and NPK production from biodigesters.
METHODOLOGY
The study was conducted between April and September 2022 by starting with collecting basic
information and designing a questionnaire for a survey. The study employed purposive sampling asa case study by selecting 30 households with biodigesters in Svay Prey commune, Prey Chhor District,Kampong Cham Province (Fig. 1) due to high household biodigester consumption. To obtainsufficient information, data such as type of bio-slurry application, size of the biodigester, type ofsubstrates used for biodigesters, and crop type were collected.
To determine the NPK content in bio-slurry, samples were collected from 3 different household
digesters in the studied area, packed, and stored at 5 0C for laboratory analysis. For the lab’s activities,
these three samples were mixed then using reagents (TN, TP, TK diluting with a sample with a mass
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IJERD – International Journal of Environmental and Rural Development (2023) 14-1of 100 g for each parameter to determine NPK content following ISO 11261, 11263, and 17319
respectively whereas, total organic carbon (TC) also measured by Walkley and Black method.
Estimation of daily and annual bio-slurry production from biodigester using cow dung as a
substrate can be calculated based on the following Eq. (1). This estimation is based on the researchby Kumar et al. (2015), who found that 1 kg of cow dung produces 0.3 kg of bio-slurry, or 30%,
daily. Technically, daily manure fed into biodigesters sized 4, 6, and 8 m3 is equal to 30, 50, and 70
kg/day, respectively (Hyman and Bailis, 2018).
𝑄𝑠𝑙𝑢𝑟𝑟𝑦 (𝑡𝑜𝑛𝑠𝑦𝑒𝑎𝑟) = 𝐷𝑎𝑖𝑙𝑦 𝑚𝑎𝑛𝑢𝑟𝑒 (𝑘𝑔𝑑𝑎𝑦) × 𝑝𝑒𝑟𝑐𝑒𝑛𝑡 𝑜𝑓 𝑏𝑖𝑜 − 𝑠𝑙𝑢𝑟𝑟𝑦 𝑥 365 𝑑𝑎𝑦𝑠

(1)

Fig. 1 A map of Prey Chhor District, Kampong Cham Province
Data Analysis and Interpretation
Descriptive statistics were employed to analyze quantitative data collected in the survey, andfrequency tests were also used in the hypothesis to examine the relationship between two variables
to determine the significant difference in data. Besides this, data was also organized in tables andgraphs based on the types of questions and responses in Microsoft Excel.
RESULTS AND DISCUSSION
General Characteristics of Farm Households
Among 30 households, there are 50% of female farmers and 50% of male farmers whose age was
57±12.17 years (Table 1). The average household size was 4 ± 1.35. For the education status, 56.7%
of farmers were at the primary school level, whereas only 26.6 % went to high school, and 16.7 %were illiterate. Regarding biogas installation, 100% of biodigesters are concrete fixed-dome digesters,of the sizes 3, 4, 6, and 8 m3, 53% of biodigesters had a volume of 6 m3, while 20% were 4 m3
biodigesters. The farmers mostly raised cows, so that cow manure could be used as a main substrate
for biogas production. Of all the interviewees, 97% used cow manure as a substrate.
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Nutrients in Bio-Slurry / Substrate Source (Cow)
Table 2 shows that bio-slurry contained 0.2% total nitrogen (TN), 0.22% total phosphorus (TP),0.44% total potassium (TK), and 2.77% total organic carbon (TOC). With this result, the C/N ratio
was calculated to be 13.9, while the pH was 7.11. In contrast, based on the study of (Kumar et al.,2015), the nutrient content of bio-slurry from cattle was between 1.4% and 1.8% of TN, 1.1-2% ofTP, and 0.89-1.2% of TK. The result of low NPK content in this study might be due to different cow
species and feed types used for cows in Cambodia, whereas they raised the local breed of cattle andmostly fed their local grass and brewery waste with a high protein content.
Moreover, the nutrient content of compost consisted of 0.5-1.5% TN, 0.4-0.8% TP, and 0.51.9% TK, while the nutrient content of fresh cattle manure contained 0.5-1% TN, 0.5-0.8% TP, and0.5-0.8% TK in the same study. Additionally, Bonten et al. (2014) indicated that cattle slurry consistsof 1.3-1.5% of N, 0.3-2.8% of P, and 0.3-1.4% of K, whereas swine slurry consists of 1.8-2.7% ofN, 0.8-3.3% of P, 0.5-0.8% of K, respectively.
Table 1 General characteristics of the farmers
Variables
SexMaleFemaleAge (year)
Household size (person)
Education
Illiteracy
Primary school
Secondary school
High school
Type of biodigester
Concrete fixed dome
Other types
Digester size (m3)3468Type of substrate
Cow manure
OthersNumber of interviewees
PersonPercentage (%)

Mean ± SD
57 ± 12.17
4 ±1.35-1515
5170830
0
1616
329
1

50.00
50.00
56.70
0.00
26.66
100.00
0.00
3.00
20.00
53.00
10.00
97.00
3.00

Table 2 Nutrient content in bio-slurry freshly produced from cow manureNo.
123456Parameters
Total nitrogen (TN)Total phosphorus (TP)Total potassium (TK)
Total organic carbon (TOC)
C: N Ratio
pHUnitTesting result (%)

g/100gg/100gg/100gg/100g
g/g
-0.20
0.22
0.44
2.77
13.90
7.11

Estimation of Daily Bio-slurry Production
Table 3 compares the annual bio-slurry production by three sizes of biodigesters. Generally, the 8 m3
digester requires 70 kg/day of cow manure and can produce 21 kg of bio-slurry daily or 8 tons/a. For
a 6-m3 sized digester, the daily and annual bio-slurry production would be 15 kg and 5 tons/year
respectively for the 4-m3 digester, about 9 kg of bio-slurry is produced per day, or 3 tons/year. Incomparison with Kumar et al. (2015), animal manure generated 256.2 Mt each year, and total annual
biogas slurry was 76.8 Mt/year which was a huge amount of bio-slurry produced from biodigesters
and they were recoverable approx. 60% of total produced dung (resourced from cattle+ buffalo) whileⒸ ISERD

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the total estimated potential of biogas plants was in total 12 million plants for generating biogas andbio-slurry daily in India.
Table 3 Estimation of daily and annual bio-slurry production
Digester volume (m3)Daily slurry production(kg/day)

Annual slurry (ton/year)

46891521358Figure 2 shows the comparison of NPK content in bio-slurry annually produced in the threesizes of biodigesters. It is seen that the annual TK yield in bio-slurry was higher than the others.
Starting with annual TK production in bio-slurry, it varied from 1.45 to 3.37 tons/year of P produced
from an 8 m3 sized digester, while TN of 0.66 tons/year was obtained from one unit of a 4 m 3 sizeddigester, 1.1 tons/year for a 6 m3 sized digester, and 1.53 tons/year for an 8 m3. However, the finding
was relatively low when compared to Kumar (2015) who found that nitrogen content was 1.15 Mt in
76.8 Mt slurry produced annually. Additionally, Martinez-Suller et al. (2010) found that the average
TN, TP, and TK yields from cattle slurry were 3.43 kg/m3, 0.56 kg/m3, and 4.41 kg/m3 respectively.
NPK in bio-slurry ( tons/yr.)

4Nitrogen (N)Phosphorus (P)Posstasium (K)

32104

68

Volume of biodigester (m3)

Fig. 2 Comparison NPK content in bio-slurry annually produced in different sizes of digester
Proportion of the Farmers Applying Bio-Slurry for Crop Production
It is observed that most of the farmers applied the slurry in solid state (Fig. 3). About 63.3 % of thefarmers applied solid slurry for their crop production, whereas only 13.3% consumed liquid bioslurry, and around 23% (Table 4) used both solid and liquid bio-slurry in their crop production.
Table 4 Type of slurry application
Type of slurry application
WetDryBothNumbers

Percentage (%)

4197

13.33
63.33
23.33

Nevertheless, all the interviewees were willing to utilize dry or solid slurry for their riceproduction, and they all also applied liquid slurry for leafy vegetables such as water morning glory,
lettuce, onion leaf, mustard greens, and spinach. Additionally, 70% of the farmers utilized solid slurry
for fruity vegetables like eggplants, cucumbers, sweet peppers, and chili peppers, whereas 30%
preferred liquid slurry. On the other hand, it is observed that before having biodigesters, therespondents used chemical fertilizer only, for both rice and vegetables. After the installation of biodigesters, the consumption of chemical fertilizer for rice production was reduced by 39% and by 35%Ⓒ ISERD49

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for vegetable production. Concerning the liquid slurry application, one study (Musse et al., 2020)
reiterated that a mixture of bio-slurry in liquid state and N-inorganic fertilizer applications provided
a high yield of green bean (fruity vegetable) and improve both soil physio-chemical properties.

Fig. 3 Types of slurry application and percentage of chemical fertilizer use in different crops
CONCLUSION
In conclusion, bio-slurry production varies based on the amount of cow dung fed into biodigesters
daily. In the meantime, the nutrient content of bio-slurry had higher potassium (K) than other subnutrients such as nitrogen (N) and phosphorus (P). For bio-slurry application, most farmers always
applied solid bio-slurry for crops, and all farmers prefer to use solid slurry for rice and liquid forms
for vegetables. Furthermore, the use of slurry can replace and reduce chemical fertilizers in crop
production. Finally, the farmers still mix chemical fertilizer with bio-slurry because they think it iskey to obtaining good quality and high-yield crops. Therefore, further research should be performed
to identify the impacts of bio-slurry on crop growth and yield for better documentation and wider
adoption.
ACKNOWLEDGEMENTS
The study was made possible thanks to the project “Reduction of Greenhouse Gas Emission throughPromotion of Commercial Biogas Plant in Cambodia” implemented by the United Nations Industrial
Development Organization (UNIDO), which provided funding for this survey study, and I would liketo acknowledge to “Higher Education Improvement Project (HEIP)” funded by the World Bank toRoyal University of Agriculture (RUA) for sponsoring my master’s degree study. Also, many thanks
to all the farmers and local authorities in the Prey Chhor District for their kindness in allowing forthe survey.
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Kumar, S., Malav, L.C., Malav, M.K. and Khan, S.A. 2015. Biogas slurry, Source of nutrients for eco-friendlyagriculture. International Journal of Extensive Research, 2, 42-46, Retrieved from URL https://cyberleninka.org/article/n/281060.pdf
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