Classification. Rice husks as well as empty seeds are pyrolised and used as a soil amendment in the rice seed beds and the vegetable gardens.

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1 Production and use of rice husk biochar in rice seed beds and vegetable production. Cambodia - ក រផល ត ន ងប រ ប រ ស ជ ធ យ ងអង ក មល ថ ន លស ណ បន ងដ ណ បន ល (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 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: 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: Contact person: Lean Hak Khun, SOFDEC/LAREC, kleanghak@yahoo.com, sofdec@camintel.com 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)

2 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 Level of technical knowledge Prevention Mitigation / Reduction Rehabilitation 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) Altitude (m a.s.l.) Landform Slope (%) > 4000 mm mm mm mm mm mm mm mm < 250 mm > <100 plateau / plains ridges mountain slopes hill slopes footslopes valley floors flat gentle moderate rolling hilly steep very steep Soil depth (cm) >120 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 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) < ,000 1,000-10,000 >10,000 Land user: Individual / household, medium scale land users, common / average land users, men and women Population density: 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

3 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 Equipment Costs (US$) % met by land user - Kiln % TOTAL % Maintenance/recurrent activities - Biochar making - Adding Biochar to the fields after the compost was plowed in, and harrowing. Maintenance/recurrent inputs and costs per unit per year Inputs Costs (US$) % met by land user Labour % 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

4 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 increased nutrient cycling recharge increased soil organic matter / below ground C increased biological pest / disease control increased soil moisture Off-site benefits Ecological disadvantages 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. 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. 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

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