Production and use of rice husk biochar in
rice seed beds and vegetable production.
Cambodia - ការផលិត
នឹងប្រើប្រាស់ជីធ្យូងអង្កាមលើថ្នាលសំណាបនឹងដំណំាបន្លែ
(Khmer)
Rice husks as well as empty seeds are pyrolised and used
as a soil amendment in the rice seed beds and the
vegetable gardens.
Biochar is the residue left after the pyrolysis of any organic matter and is used as a soil amendment. Pyrolysis
occurs when the organic matter is heated in anaerobic conditions, which is usually done in specially designed
kilns. Sometimes it is also made in a conventional fire, which is extinguished before the char turns to ash.
Agricultural wastes like rice husks or unfilled grains are mainly used. Biochar can have many positive effects
on the soil and plants: -It buffers the pH, and has usually a high pH due to theash content. -Due to its porous
structure, it holds water and serves as refuge for microorganisms. -It absorbs and adsorbs nutrients, both
cations and anions. They are available for the plant roots. -It can increase the resistance of plants to diseases.
Due to all these effects, the increased yields are higher than those that can be achieved only through the
nutrients contained in the Biochar itself. Biochar is and was used in many parts of the world as soil
amendment, with some benefits persisting for centuries. In Cambodia it was used during the Pol Pot regime
to reduce the smell of the human faeces that were used on the fields due to a lack of other fertilizers. Today
research in the Biochar domain is increasing, especially since the discovery of the man-made terra preta soils
in South America.
Biochar is mainly used to increase the fertility, water holding capacity and carbon content of the soil. The fact
that the benefits of Biochar addition to the soil remain for several years, unlike chemical fertilizers, makes it
attractive to farmers. Other purposes, like the increased resistance of plants to diseases and buffering of
nutrients are also of importance.
Biochar was introduced or reintroduced trough different NGOs, JICA (Japanese International Cooperation
Agency) in this case study. Because of knowledge exchange between farmers, a rice husk char/ash mix, as
residue from the pottery baking, was used already in 2011. In 2013 JICA borrowed a Biochar kiln to the local
farmer self-help group with a training, so they could produce Biochar by themselves. The inner part of the kiln
(cf. technical drawing) is filled with wood and lit. It is then put into an empty oil barrel, which is filled with rice
husks. The heat pyrolyses the husks from the bottom to the top of the barrel, and the gases are burned in the
inner part of the kiln and the chimney. Just before the upper part is pyrolysed, the husks are extinguished.
There is a weight loss of about 50 to 60 % caused by this process. The Biochar is added to the fields after
ploughing, and the fields are harrowed. In this case study, Biochar is used both in rice seed beds and in a
vegetable patch. Concentrations of 0.5 kg/m2 are used in the rice seed bed, and 2.5 kg for the vegetables.
Due to the little available quantities of husks, Biochar is not applied to the field yet. The use of Biochar is
spreading quickly from farm to farm
The analysed area is flat (slope < 2%), with a tropical climate (dry season from November to May and wet
season from June to October), and the soils are mostly sandy or loamy. The soil has a low fertility, contains
little organic matter, and acidifies. The area has been deforested a long time ago, and the groundwater table
is rather high (1-2 m during the dry season, on the surface during wet season). Due to climate change,
farmers notice more erratic rainfall, temperature rises and more recurrent droughts. Rice is the predominant
crop grown in the area, since it serves as staple food (mix subsistence and commercial activities). Cattle are
usually grazing on the fields after the harvest, without much control. Thus the cattle grazes too often and too
much on the same spot, leading to degradation. The increasing migration rate (the young generation leaves
the villages to work in the cities, garment industry or abroad) results in a decrease of available labour force in
the area which has detrimental effects on the agricultural activities. Furthermore, the civil war in the 1970s
(Khmer Rouge) led to the loss of agricultural knowledge. Several NGOs are trying to re-establish the
knowledge.
left: Oil barrel where the husks are
pyrolised, and the chimney of the
burning chamber. (Photo: Stefan Graf)
right: Burning chamber and part of
the chimney. A wooden fire is started
inside, and the burning chamber is
then put into the oil barrel which is
then filled with rice husks. (Photo:
Stefan Graf)
Location: Kampong Chhnang
Region: Kraing Leav
Technology area: 0.1 - 1 km2
Conservation measure: agronomic
Stage of intervention: mitigation /
reduction of land degradation
Origin: Developed externally /
introduced through project, recent
(<10 years ago)
Land use type:
Cropland: Annual cropping
Climate: subhumid, tropics
WOCAT database reference:
T_CBD009en
Related approach:
Compiled by: Stefan Graf,
Date: 2014-08-14
Contact person: Lean Hak Khun,
SOFDEC/LAREC, www.sofdec.com,
[email protected],
[email protected]
Classification
Land use problems:
- Soil fertility decline, water availability (expert's point of view)
Water availability. Interestingly the farmer says that soil fertility is not a problem, as the farmers know about the use of
compost. The compost application is the problem. (land user's point of view)
Land use
Climate
Degradation
Conservation measure
Annual cropping
subhumid
Chemical soil deterioration:
fertility decline and reduced
organic matter content,
acidification
Agronomic: Organic matter /
soil fertility
Stage of intervention
Origin
Prevention
Mitigation / Reduction
Rehabilitation
Level of technical knowledge
Land users initiative
Experiments / Research
Externally introduced: recent (<10 years ago)
Agricultural advisor
Land user
Main causes of land degradation:
Direct causes - Human induced: soil management
Indirect causes: labour availability
Main technical functions:
- increase in organic matter
- increase in nutrient availability (supply, recycling,…)
Secondary technical functions:
Environment
Natural Environment
Average annual rainfall
(mm)
> 4000 mm
3000-4000 mm
2000-3000 mm
1500-2000 mm
1000-1500 mm
750-1000 mm
500-750 mm
250-500 mm
< 250 mm
Soil depth (cm)
0-20
20-50
50-80
80-120
>120
Altitude (m a.s.l.)
> 4000
3000-4000
2500-3000
2000-2500
1500-2000
1000-1500
500-1000
100-500
<100
Landform
Slope (%)
plateau / plains
ridges
mountain slopes
hill slopes
footslopes
valley floors
Growing season(s): 210 days(June-December)
Soil texture: coarse / light (sandy), medium
(loam), fine / heavy (clay)
Soil fertility: medium, low
Topsoil organic matter: low (<1%)
Soil drainage/infiltration: good, medium
flat
gentle
moderate
rolling
hilly
steep
very steep
Soil water storage capacity: medium, low
Ground water table: on surface, < 5 m
Availability of surface water: good, poor /
none
Water quality: poor drinking water
Biodiversity: low
Tolerant of climatic extremes: temperature increase, seasonal rainfall increase, seasonal rainfall decrease, droughts / dry
spells, decreasing length of growing period
Sensitive to climatic extremes: floods
Human Environment
Cropland per
household (ha)
<0.5
0.5-1
1-2
2-5
5-15
15-50
50-100
100-500
500-1,000
1,000-10,000
>10,000
Land user: Individual / household, medium
scale land users, common / average land users,
men and women
Population density: 10-50 persons/km2
Annual population growth: 0.5% - 1%
Land ownership: communal / village,
individual, not titled
Land use rights: communal (organised),
individual
Water use rights: open access (unorganised)
(Land users have a title that is not recognized
by the state.)
Relative level of wealth: average
poor
Importance of off-farm income: 10-50% of
all income: handicraft, remittances and factory
work
Access to service and infrastructure: low:
health, technical assistance, market, drinking
water and sanitation; moderate: education,
energy, financial services; high: employment
(eg off-farm), roads & transport
Market orientation: subsistence (self-supply),
mixed (subsistence and commercial)
Mechanization: animal traction, mechanised
Livestock grazing on cropland: yes
Technical drawing
Biochar kiln. In the inner part, the combustion
chamber, a wooden fire is lit. The burning
chamber is then placed in the oil barrel, which
is filled with rice husks. The heat pyrolyses the
husks, the gas burn in the chamber and
chimney. When pyrolysis is almost completed,
the char is extinguished. (Stefan Graf)
Implementation activities, inputs and costs
Establishment activities
- Biochar kiln
Establishment inputs and costs per unit
Inputs
Costs (US$) % met by land
user
Equipment
Maintenance/recurrent activities
- Biochar making
- Adding Biochar to the fields after the compost was
plowed in, and harrowing.
- Kiln
50.00
0%
TOTAL
50.00
0.00%
Maintenance/recurrent inputs and costs per unit per year
Inputs
Labour
Costs (US$) % met by land
user
20.00
100%
0.25
100%
4.00
100%
24.25
100.00%
Equipment
- machine use
Agricultural
- rice husks
TOTAL
Remarks:
The factors affecting the cost the most are the biochar kiln, and the amount of added Biochar.
The costs are indicated per unit; a unit is one biochar kiln used on 1 a. The costs were calculated in 2014 for the vegetable
beds, where the farmer uses around 2.5 kg/m2. He also uses Biochar on the rice seedling bed, with concentrations of around
0.5 kg/m2, 5 times less than in the vegetable patch. In the vegetable patch the farmer plants cucumber, pumpkin, onion,
watermelon and leaf vegetables in the early wet season, before planting rice.
Assessment
Impacts of the Technology
Production and socio-economic benefits
Production and socio-economic disadvantages
increased crop yield
increased expenses on agricultural inputs
increased labour constraints
Socio-cultural benefits
Socio-cultural disadvantages
improved food security / self sufficiency
improved health
Ecological benefits
Ecological disadvantages
increased nutrient cycling recharge
increased soil organic matter / below ground C
increased biological pest / disease control
increased soil moisture
Off-site benefits
Off-site disadvantages
Contribution to human well-being / livelihoods
Increased income, less expenses on pesticides.
Benefits /costs according to land user
Benefits compared with costs
short-term:
long-term:
Establishment
slightly positive
positive
Maintenance / recurrent
positive
not specified
The costs for the pyrolysis kiln were not borne by the land user. But as the farmer of this case study wants to build an own kiln as
soon as the NGO needs it again, it is positive.
Acceptance / adoption:
100% of land user families (100 families; 100% of area) have implemented the technology with external material support.
Considering only the farmers applying the technology with this stove. Other farmers buy Biochar, or burn the rice husks and
extinguish them. But those farmers are nearly impossible to quantify as it changes quickly. The support was the kiln, which is
only a small part of the costs.
0% of land user families (0 families; 0% of area) have implemented the technology voluntary. Considering only the farmers
applying the technology with this stove. Other farmers buy Biochar, or burn the rice husks and extinguish them. But those
farmers are nearly impossible to quantify as it changes quickly.
There is strong trend towards (growing) spontaneous adoption of the technology. In another area of Cambodia where the
Ministry of Agriculture, Forestry and Fisheries (MAFF) is doing Biochar research, there was such a strong adoption of Biochar
use that there are no more control areas. In Kampong Chhnang, the use of Biochar starts to spread now.
Concluding statements
Strengths and
how to sustain/improve
Weaknesses and
how to overcome
Soil amendment with long-term effect, as Biochar has a long
The energy produced during the pyrolysis is wasted.
Use it
half-life period.
Minimal disturbance of the soil, like no-till, to to power engines or as heating source. This would only be
avoid its oxidation. Addition of clay in sandy soils, to build clay viable on large-scale kilns.
humus and clay Biochar complexes.
Buffering and raising of the pH, especially in sandy soils.
Keep applying Biochar, together with other organic matter
(mulch or compost).
Less washing out of nutrients.
Add Biochar together with
clay in sandy soils, to enhance soil structure.
Less insect damages where Biochar is applied.
Use
Integrated Pest Management, crop rotation and intercropping.
Good growth of vegetables, with increased yields especially for
onions.
Keep applying Biochar with compost.
The rice seedlings are stronger, and the roots break less while
transplanting, and the plants recover quickly.
Keep applying
Biochar with compost.
The plants survive a short dry spell better.
Biochar with compost.
Keep applying
Substrate to make Biochar (rice husks) is difficult to find in the
area in big amounts, as only small rice mills are working there.
Rice husks are wasted in other places. Networking with
other villages. Use other (waste) sources of organic matter like
leaves.
Increased workload for the Biochar production (compensated
by the increased yields).
Use a bigger kiln to decrease the
workload.
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