Implemented by the Department of Land resource management from the Cambodian General Directorate of Agriculture (DALRM/GDA).

Several trainings and demonstration are organized in each village annually, on different practices:

• Cover crop implementation
• Diversification of cropping systems
• Appropriate scale mechanization (land leveling, reduce tillage, green sowing…).

Training and technical support can be conducted through

• Individual monitoring
• Focus group discussions and feedback sessions (~10 farmers)
• Field demonstration and training (~30 farmers).

In 2023, 12 field trainings and demonstrations were organized as well as 9 focus group discussions, with 510 participants (including 135 women).

All trainings and group discussions are conducted in khmer language, as well as the training material and posters used.

PHOTOGALLERY

Soil sampling and processing

Within each farmer field an area of 1 ha was delimited (50×200m), and five sampling site of 4 × 4 m were marked (four in lowland area). Five sub-samples and one bulk density sample were collected per sampling site at four soil depths (0-10, 10-20, 20-30, 30-40 cm). The five sub-samples were composited to form one composite sample per sampling site. Each composite sample for a given soil depth was constituted from the five sub-samples collected at each sampling point to manage the spatial variability inside the sampling area. One soil core sample was collected on the middle of the sampling site to measure the bulk density (ρb). A small pit was dug in the center of each sampling site and bulk density samples were collected using core samplers of 5 cm in diameter and 5 cm in height, oven dried at 105 °C for 48 h. Each sampling point and pit position were georeferenced.  All soil samples are stored at the Cambodian Conservation Agriculture Research for Development Center (CARDEC, Bos Khnor, Chamcarleu district,  Kampong Cham province, 12.179221° N, 105.323134° E) for further analysis including the physical fractionation of the soil organic matter (POC and MAOC) and infra-red spectroscopy calibration.

Texture and Soil organic carbon and nitrogen analyses

After the sampling campaign, the 5 composite samples per field were air-dried for 2 to 3 weeks and sieved at 2 mm.  Composite soil samples were collected to measure the texture, total soil carbon and nitrogen by dry combustion, and carbonates content (upland). Soil texture was determined through the pipette method (ISO 11277, 1998). Total carbon and nitrogen concentrations were determined through the dry combustion method. Each sample was finely ground (<150 μm) before analysis for total C and N by dry combustion using the LECO® CHN628 analyzer at the Sustainable Agroecosystems Lab, ETH Zurich University, Switzerland. The coarse fraction of bulk density samples was weighted to correct the SOC stock calculation.

Soil organic C and N stocks calculation

To correct for differences in ρb, SOC and N stocks were estimated based on an equivalent soil mass-depth basis (Ellert et al., 2002; Wendt and Hauser, 2013). We defined the reference soil mass as the lowest soil mass observed at each sampling depth, regardless of cropping systems or land use. We applied these reference soil masses to compute the SOC and N stocks.

Soil functions through Biofunctool®

Biofunctool® consists in a set of ten functional indicators that assess three main soil functions with (i) carbon transformation, (ii) soil structure maintenance and (iii) nutrient cycling (Thoumazeau et al., 2019b). These functions aggregate several biological processes which individually allow the production of goods or ecosystem services. BioFunctool® assesses these soil functions through a range of indicators. N-mineral extraction and ion exchange membrane are linked to the nutrient cycling function. Permanganate oxidizable carbon (POXC), indicator which quantify labile soil C, SituResp to assess basal soil respiration in-situ, Bait Lamina for soil mesofauna activity and cast density are used to assess Carbon transformation function (Culman et al. 2012; van Gestel, Kruidenier, Berg 2003; Thoumazeau et al. 2017). They represent different and complementary process stages of soil carbon cycle (Hurisso et al. 2016). Regarding soil structure maintenance, aggregates stability with both surface aggregates (0-2cm) and soil aggregates (2-10cm) to assess aggregates resistance to immersion and slacking, Beerkan test for water infiltration rate and Visual Evaluation of Soil Structure (VESS) for soil structure are used (Bissonnais 1996; De Roo, Hazelhoff, Heuvelink 1992; Guimarães, Ball, Tormena 2011). These indicators constitute the core set of BioFunctool® framework and are aggregated in a Soil Quality Index (SQI). Biofunctool was used for the baseline in the lowland but without covering all fields that were sampled. It is expected to use Biofunctoll under a synchronic approach assessing the impacts of different practices and cropping systems after several years of implementation.

Mid infra-red spectroscopy

All these soil samples are used to calibrate and validate mid infra-red spectroscopy. This activity refers to a global activity of the Department of Agricultural Land Resources Management (DALRM) in partnership with CIRAD and aiming at calibrating and validating the MIR for the main soil types of Cambodia. Several soil databases are used representing a total of > 2,500 georeferenced samples.

Physical fractionation of the soil organic matter

In addition to the SOC and N concentrations from the bulk soil samples, the fractionation of the soil organic matter into two main fractions (particulate organic carbon/POC and mineral associated organic carbon/MAOC) could be conducted representing an additional assessment of the impacts of the practices on the SOC pools.

Ongoing analysis. In addition to the Dei Meas pilot, two PhD studies are ongoing:

• Assessing the impacts of conservation agriculture-based cropping systems on (i) soil organic and nitrogen stocks (including the fractions) under a diachronic analysis (10 years), (ii) greenhouse gas emissions for cassava-based cropping systems (assessment on 2 cropping seasons), and (iii) quantifying all inputs of biomass (quantities and qualities) coming from the main crops and cover crops used including the root systems.
• Assessing the impacts of conservation agriculture-based cropping systems on SOC fractions including soil microbial communities, (ii) and on a range of ecosystem services (above and belowground).

These two PhD studies along with other initiatives contribute to strengthen the MRV system of Dei Meas.