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The determination of changes in soil organic carbon (SOC) content under different cropping systems is necessary for policy development oriented towards soil conservation, C sequestration, and future C credit markets. The aim of this study was to generate an open SOC dataset resulting from a systematic literature search related to the agricultural systems for Southeast Asia. The dataset has 209 articles and 4341 observations on soils of cropping systems in this region from articles published between 1987 and 2023. This dataset included different management practices, land uses, soil sampling depth, and length of SOC content assessment. In addition, inherent features of crop production reported in the experiments were included in the dataset. This dataset can be applied to quantify and compare the impact of different land uses or management practices on SOC content, providing foundational knowledge towards identifying sustainable practices. Lastly, it is a useful guide for future regional SOC sequestration policies and the development of C credit markets.

CONTEXT: Over the past two decades, the Mekong region has experienced significant transformation of its agricultural sector from subsistence farming to export crops driven by the expansion of agricultural land and of irrigation, plus intensification thanks to mechanization and the use of chemical inputs. In the context of agrarian transition, maintaining “organic by default” rice farming systems that do not rely on chemical inputs, is challenging. OBJECTIVE: Based on a case study in Preah Vihear, the organic province of Cambodia, this paper examines whether organic rice certification can maintain “organic by default” practices in a context of unprecedented agricultural intensification. METHODS: Using agrarian diagnosis, we investigated the impacts of an organic rice certification scheme on the future of organic rice-based farming systems. We built a functional typology of five farming systems that co-exist in the study area to understand the roles of organic rice in each system. RESULTS AND CONCLUSIONS: From an economic perspective, organic rice is less profitable than recently introduced cash crops, e.g. cassava, cashews. The positive impact of certification of organic rice is threatened by lock-in factors, e.g. labor diversification in both farming and non-farming activities, cash flow management, the certification process, leading farmers to abandon organic rice for cash crops for export. We discuss the key role of agricultural cooperatives in the certification process of organic rice. SIGNIFICANCE: The paper questions the capacity of a certification scheme to keep up with the process of intensification that undermines the profitability of the remaining “organic by default” rice systems. Beyond the significance of the results in the study area, one of the last strongholds of traditional rice systems in Cambodia, the paper illustrates the disappearance of “organic by default” rice systems in the whole country as well as in the Mekong region.

Document technique de synthèse des résultats d'un dispositif longue durée mis en place au Cambodge avec une comparaison de 4 systèmes de culture à base de riz avec 3 niveaux de fertilisation. Le document présente le bilan des indicateurs de croissance et développement des cultures de riz mais aussi de plantes de couverture en rotation, évolution de la fertilité du sol, de la pression des bioagresseurs (dispositif géré sans insecticides ni fongicides).

In the Northwestern uplands of Cambodia, the commodification of agriculture in the 2000 s substituted the traditional rotational and diversified cropping systems with monocropping of commercial crops such as maize and cassava. Driven by high market demand, this transition was associated with deforestation, erosion of soils and biodiversity as well as pollution from increased use of chemical inputs. Land degradation observed after a few years of intensive monocropping undermined the sustainability of the overall agricultural system. However, lessons learned from previous failures of crop boom-bust cycles did not materialize as an incentive to adopt alternative sustainable practices. Along with local villagers we developed a role-play game to investigate farmers' decision-making in relation to land-use transitions and their participation in a Conservation Agriculture (CA) initiative aimed at mitigating land degradation. The game revealed that farmers were still trapped in the boom-bust cycle with commercial crops. Market opportunities and high, short-term economic returns are key parameters in the decision-making process, which mostly overrides environmental aspects. This study shows the importance of opportunity windows for development interventions, the crucial role of farming communities in co-designing alternative cropping systems and the potential of social learning devices to bring CA to scale.

Conservation agriculture (CA) is one strategy with which both sustainability and productivity can be achieved by improving soil health. However, linkages between practices, soil health and cropping system performance remain poorly disentangled. We assessed the relationships between soil health and cropping system performance for three maize-based cropping systems in New Caledonia. Two CA systems, one with direct seeding into a mixed species dead mulch (CA-DM) and one into a stylo living mulch (CA-LM), were compared to a conventional tillage (CT) system. CA vs. CT experiment started in 2011, whereas the differentiation between CA-DM and CA-LM was initiated in 2017 only. In 2018, soil health was evaluated using Biofunctool®, a set of ten in-field tools that assess soil carbon transformation, structure maintenance and nutrient cycling functions. The performance of the three cropping systems were assessed by monitoring weeds, maize growth and yield components. Structural equation modelling (SEM) was used to disentangle the links between agricultural management, soil health and cropping system performance. Soil structure maintenance and nutrient cycling functions were higher under CA-DM and CA-LM than under CT, and carbon transformation function was higher under CA-DM than under CT and CA-LM. Overall, the soil health index (SHI) was 1.3-fold higher under CA systems than under CT. Cropping system management had both direct and indirect effects on soil functioning and crop productivity leading to a 1.3-fold higher yield under CA than under CT. The direct and indirect effects of CA systems on soil health had positive impacts on ecosystem services (i.e., productivity, weed regulation and soil ecosystem services). Such integrative approaches that account for the relationships and possible trade-offs between cropping system components enable a better understanding of the effects and the performance of practices, and support adaptive agricultural management.

Rice production in Southeast Asia is significantly affected by root-parasitic nematodes (RPN). The Green Revolution has encouraged new agricultural practices (e.g. intensive monoculture, high yielding rice variety) to respond to the high rice demand; however, these methods have promoted the spread of these pests. The recent banning of chemical nematicides resulted in a need for alternative sustainable control strategies. In the present study, we assessed the effects of a direct-seeding mulch-based cropping system (DMC) vs conventional plough-based tillages (CT) on soil properties, rice yield and RPN communities during a two-year trial in Cambodia. Our results show that on average the population densities of RPN were significantly higher in DMC than in CT. Molecular identification revealed only two RPN species associated with roots: Meloidogyne graminicola, not previously reported from Cambodia, was predominant and was present throughout the plant's development, whereas Hirschmanniella mucronata was only found at the tillering and milky stages. We conclude that DMC had a significant positive impact on rice yield, despite higher RPN short-term pressure. In order to increase the efficiency of such cropping systems, further studies and an evaluation of the long-term relationships between DMC, the nature of cover crops used, the soil biota including RPN, and rice yield should be conducted.

Agroecology is a promising way to synergize climate change mitigation and adaptation. It builds on the practices and knowledge of smallholder farmers to address food insecurity while reducing dependence on fossil fuels and avoiding land degradation. However, bringing agroecology to scale remains an important challenge when it comes to addressing the broader policy, social and economic contexts. Agroecology research and resulting evidence on what makes the application of agroecology principles successful are typically generated at small spatial scales. Policies instruments and intervention mechanisms that would create enabling conditions for local agroecological innovations on a large scale are still largely missing. We investigated the approaches, methods and resources employed by research-development stakeholders to promote agroecological practices in Southeast Asia. We considered two dimensions related to the modalities of intervention, namely (i) push-pull interventions and (ii) transition-conversion approaches. The first dimension refers to the distinction between push interventions – where financial, technical, material and/or organizational support is provided to targeted actors allowing them to modify their practices (e.g. subsidies and farm extension work) – and pull interventions that target the broader social and economic conditions in which actors make decisions in order to favour desired practices (e.g. sensitization and price premiums, regulations on agricultural practices e.g. restricted pesticide use). The second dimension refers to a practical opposition between approaches that promote a strict conversion from one set of practices to another seen as more desirable and approaches that allow (or even plan) for a transition between different practices. We illustrate these multiple dimensions of transformative adaptation through concrete examples related to conservation agriculture and organic farming in Laos and Cambodia.

As a response to the worldwide challenge raised by soil degradation, Conservation Agriculture (CA) was proposed to help restoring the three main soil functions, i.e. carbon transformation, nutrient cycling and structure maintenance. However, there is still a lack of integrative studies that assess the overall impact of CA on soil health. To fill the gap, Biofunctool®, a set of in-field indicators, was developed to monitor changes in soil biological functioning. In this study, Biofunctool® was used to assess the impact of a conventional tillage (CT) and three CA annual-based cropping systems on soil health on a Cambodian Oxisol. Eight indicators related to the three soil functions were monitored and integrated into a Soil Quality index (SQI), i.e. the Biofunctool® Index. Overall, we found that soil health was twice higher under the CA treatments than under CT treatment. Although it was similar in the three CA treatments, the contribution of each soil function to the soil health diverged. An analysis of soil carbon dynamics also showed that CA support short-term soil organic carbon stabilization compared to CT. This study demonstrates that Biofunctool® is a robust, relevant, time-and cost-effective in-field assessment tool that can be used in multiple ways including cropping system management, capacity building of local stakeholders, and policy dialogue.

Rice production in Southeast Asia is significantly affected by root-parasitic nematodes (RPN). The Green Revolution has encouraged new agricultural practices (e.g. intensive monoculture, high yielding rice variety) to respond to the high rice demand; however, these methods have promoted the spread of these pests. The recent banning of chemical nematicides resulted in a need for alternative sustainable control strategies. In the present study, we assessed the effects of a direct-seeding mulch-based cropping system (DMC) vs conventional plough-based tillages (CT) on soil properties, rice yield and RPN communities during a two-year trial in Cambodia. Our results show that on average the population densities of RPN were significantly higher in DMC than in CT. Molecular identification revealed only two RPN species associated with roots: Meloidogyne graminicola, not previously reported from Cambodia, was predominant and was present throughout the plant's development, whereas Hirschmanniella mucronata was only found at the tillering and milky stages. We conclude that DMC had a significant positive impact on rice yield, despite higher RPN short-term pressure. In order to increase the efficiency of such cropping systems, further studies and an evaluation of the long-term relationships between DMC, the nature of cover crops used, the soil biota including RPN, and rice yield should be conducted.

Agroecology is a promising way to synergize climate change mitigation and adaptation. It builds on the practices and knowledge of smallholder farmers to address food insecurity while reducing dependence on fossil fuels and avoiding land degradation. However, bringing agroecology to scale remains an important challenge when it comes to addressing the broader policy, social and economic contexts. Agroecology research and resulting evidence on what makes the application of agroecology principles successful are typically generated at small spatial scales. Policies instruments and intervention mechanisms that would create enabling conditions for local agroecological innovations on a large scale are still largely missing. We investigated the approaches, methods and resources employed by research-development stakeholders to promote agroecological practices in Southeast Asia. We considered two dimensions related to the modalities of intervention, namely (i) push-pull interventions and (ii) transition-conversion approaches. The first dimension refers to the distinction between push interventions – where financial, technical, material and/or organizational support is provided to targeted actors allowing them to modify their practices (e.g. subsidies and farm extension work) – and pull interventions that target the broader social and economic conditions in which actors make decisions in order to favour desired practices (e.g. sensitization and price premiums, regulations on agricultural practices e.g. restricted pesticide use). The second dimension refers to a practical opposition between approaches that promote a strict conversion from one set of practices to another seen as more desirable and approaches that allow (or even plan) for a transition between different practices. We illustrate these multiple dimensions of transformative adaptation through concrete examples related to conservation agriculture and organic farming in Laos and Cambodia.

The Regional forum on Agroecology Futures represented the closing session of the ACTAE Project1 “Toward an agroecological transition in South East Asia” funded by AFD (Agence Française pour le Développement). It took place in Siem Reap, Cambodia, on 6th – 8th of November 2018. It has been the biggest event on agroecology in the Mekong Region since the Regional Symposium organized by the UN Food and Agriculture Organization (FAO) in November 2015, in Bangkok, Thailand. Over 260 participants from 21 nationalities gathered to discuss the futures of Agroecology during an unprecedented Regional Forum. The event was co-organized by the General Directorate of Agriculture (GDA) of Cambodia, CIRAD and GRET in a joint effort to promote agroecology. The overall aim of the forum was to build a momentum around the different dimensions of Agroecology that should be addressed, and consolidate a Regional Agroecology stakeholders' coalition by wrapping up the achievements of ACTAE project (Towards an Agroecological Transition in South-East Asia, AFD) and discussing the future of regional initiative in Agroecology. Over 3 days, the participants could learn, share and network through 74 presentations in plenary and parallel sessions, an innovation and knowledge fair (with over 20 booths), a poster session (25 were presented) and a seed swap where more than 60 different plant species were exchanged. Agroecology being diverse and multidimensional, a broad range of issues were addressed such as the fundamental role of crop biodiversity, the highly preoccupying status of agrochemical use in the region, the need for appropriate-scale mechanization, the importance of innovative and participatory intervention mechanisms, the recognition and integration of Indigenous Knowledge, the capacity building of the new generation, the marketing of agroecological products… A panel discussion bringing together representatives from AFD, the UN Food and Agriculture Organization (FAO), the Livelihood Trust

The proposed 4 per mille initiative aims at assessing soil organic carbon dynamics affected by land management in various and numerous ecosystems. However, assessments based on soil organic carbon dynamics face methodological and experimental shortages. First, SOC assessments may not be sensitive enough to rapid land management changes, due to the long term turnover of SOC (Dignac et al., 2017). Indicators based on soil fractions seems more adapted but this method is strenuous and time consuming and not well adapted for land managers. A new framework was proposed by Hurisso et al., (2016) to assess soil carbon dynamics, linking two indicators of soil carbon fractions (POXC and Basal Soil Respiration). This framework proved to be sensitive to land managements, and may be applied with cost- time-effective indicators in the field. Strictly following this framework, this study presents a first in situ application of the POxC and SituResp® indicators along a perturbation gradient based on rubber tree cultivation in Thailand. The indicators were applied in five study sites to follow a pedo-climatic gradient and finally resulted in 210 sampling points. A predictive model was then developed to avoid the site-specific calibration step and the model was validated among the literature data. The aggregation of the results at the site-scale proved to provide generalizable conclusions on the soil carbon dynamics, from the conversation of an intensive cash cropping system to various rubber tree stand ages, bounded by natural forest reference. Then, the model, integrating soil properties variables, proved to be robust under the pedo-climatic conditions treated, and validated against literature data. This first in situ study and the model developed are promising for the further application of the two indicators in more contrasted contexts. The methods may easily be implemented as a preliminary assessment tool in order to conceptualize new management practices that sustain soil carbo

The Regional forum on Agroecology Futures represented the closing session of the ACTAE Project1 “Toward an agroecological transition in South East Asia” funded by AFD (Agence Française pour le Développement). It took place in Siem Reap, Cambodia, on 6th – 8th of November 2018. It has been the biggest event on agroecology in the Mekong Region since the Regional Symposium organized by the UN Food and Agriculture Organization (FAO) in November 2015, in Bangkok, Thailand. Over 260 participants from 21 nationalities gathered to discuss the futures of Agroecology during an unprecedented Regional Forum. The event was co-organized by the General Directorate of Agriculture (GDA) of Cambodia, CIRAD and GRET in a joint effort to promote agroecology. The overall aim of the forum was to build a momentum around the different dimensions of Agroecology that should be addressed, and consolidate a Regional Agroecology stakeholders' coalition by wrapping up the achievements of ACTAE project (Towards an Agroecological Transition in South-East Asia, AFD) and discussing the future of regional initiative in Agroecology. Over 3 days, the participants could learn, share and network through 74 presentations in plenary and parallel sessions, an innovation and knowledge fair (with over 20 booths), a poster session (25 were presented) and a seed swap where more than 60 different plant species were exchanged. Agroecology being diverse and multidimensional, a broad range of issues were addressed such as the fundamental role of crop biodiversity, the highly preoccupying status of agrochemical use in the region, the need for appropriate-scale mechanization, the importance of innovative and participatory intervention mechanisms, the recognition and integration of Indigenous Knowledge, the capacity building of the new generation, the marketing of agroecological products… A panel discussion bringing together representatives from AFD, the UN Food and Agriculture Organization (FAO), the Livelihood Trust

The proposed 4 per mille initiative aims at assessing soil organic carbon dynamics affected by land management in various and numerous ecosystems. However, assessments based on soil organic carbon dynamics face methodological and experimental shortages. First, SOC assessments may not be sensitive enough to rapid land management changes, due to the long term turnover of SOC (Dignac et al., 2017). Indicators based on soil fractions seems more adapted but this method is strenuous and time consuming and not well adapted for land managers. A new framework was proposed by Hurisso et al., (2016) to assess soil carbon dynamics, linking two indicators of soil carbon fractions (POXC and Basal Soil Respiration). This framework proved to be sensitive to land managements, and may be applied with cost- time-effective indicators in the field. Strictly following this framework, this study presents a first in situ application of the POxC and SituResp® indicators along a perturbation gradient based on rubber tree cultivation in Thailand. The indicators were applied in five study sites to follow a pedo-climatic gradient and finally resulted in 210 sampling points. A predictive model was then developed to avoid the site-specific calibration step and the model was validated among the literature data. The aggregation of the results at the site-scale proved to provide generalizable conclusions on the soil carbon dynamics, from the conversation of an intensive cash cropping system to various rubber tree stand ages, bounded by natural forest reference. Then, the model, integrating soil properties variables, proved to be robust under the pedo-climatic conditions treated, and validated against literature data. This first in situ study and the model developed are promising for the further application of the two indicators in more contrasted contexts. The methods may easily be implemented as a preliminary assessment tool in order to conceptualize new management practices that sustain soil carbo

The political and territorial reintegration strategy that had been implemented in Cambodia to establish peace and order in the late 1990s caused the degraded evergreen forestlands to be allocated to the demobilized Khmer Rouge families in the western regions of the country. The increasing regional demand for cereals and tubers and the highland saturation in central rice areas have driven massive immigration of smallholder farmers. Almost half a million hectares of those forestlands were thus converted in less than 15 years for annual upland cash crops development. This dramatic expansion of agricultural area, without any plan for sustainability, has exerted tremendous pressures on the natural forest resources and on biodiversity. Its effects rapidly spread on the water and soil resources of Cambodia. With conventional practices and more frequent flooding and incidents of drought, smallholder farmers could hardly sustain their livelihoods, which are mainly based on annual upland farming. Farmers with investment capacity have shifted to planting tree crops and/or to animal production in order to cope with the hazardous phenomena. This case story presents the collaborative R&D program between farmers and researchers in Battambang and Kampong Cham provinces in Cambodia. The program aimed to restore soil fertility and build the resilience of smallholder farmers to the effects of climate change while improving crop productivity and profitability of the smallholder farmers. Using the Diagnosis, Design, Assessment, Training and Extension (DATE) methodology, the project implementers designed, tested, and evaluated crop production systems that are grounded on the principles of conservation agriculture (CA). DATE is a multi-scale, multi-stakeholder participatory approach. It integrates scientific and tacit knowledge, and is composed of four components: agrarian systems diagnosis, field experiment, on-farm assessment, and pre-extension. A number of CA-based cropping systems hav

The political and territorial reintegration strategy that had been implemented in Cambodia to establish peace and order in the late 1990s caused the degraded evergreen forestlands to be allocated to the demobilized Khmer Rouge families in the western regions of the country. The increasing regional demand for cereals and tubers and the highland saturation in central rice areas have driven massive immigration of smallholder farmers. Almost half a million hectares of those forestlands were thus converted in less than 15 years for annual upland cash crops development. This dramatic expansion of agricultural area, without any plan for sustainability, has exerted tremendous pressures on the natural forest resources and on biodiversity. Its effects rapidly spread on the water and soil resources of Cambodia. With conventional practices and more frequent flooding and incidents of drought, smallholder farmers could hardly sustain their livelihoods, which are mainly based on annual upland farming. Farmers with investment capacity have shifted to planting tree crops and/or to animal production in order to cope with the hazardous phenomena. This case story presents the collaborative R&D program between farmers and researchers in Battambang and Kampong Cham provinces in Cambodia. The program aimed to restore soil fertility and build the resilience of smallholder farmers to the effects of climate change while improving crop productivity and profitability of the smallholder farmers. Using the Diagnosis, Design, Assessment, Training and Extension (DATE) methodology, the project implementers designed, tested, and evaluated crop production systems that are grounded on the principles of conservation agriculture (CA). DATE is a multi-scale, multi-stakeholder participatory approach. It integrates scientific and tacit knowledge, and is composed of four components: agrarian systems diagnosis, field experiment, on-farm assessment, and pre-extension. A number of CA-based cropping systems hav

Cambodia has been identified to be one of the most affected countries by climate change. In the past two decades, migration from the central plains to the peripheral areas changed drastically the development of the uplands, inducing tremendous degradation of natural resources. The promotion of cropping systems based on ecological intensification is of paramount importance to strengthen the resilience of small-scale farming, to mitigate the effect of climate change and to advance in farm sustainability. The aim of this study was to quantify the short-term impact of conservation agriculture (CA, direct seeding + use of cover/relay crops), on soil organic C (SOC), soil total N (STN), labile C fractions (particulate organic C - POC and permanganate oxidizable organic C - POXC), β-glucosidase and arylsulfatase activities. Established in 2009, the experimental plots were laid out in a randomized complete block design (3 replicates) with: (i) soybean under conventional tillage (CT), (ii) soybean under conservation agriculture (CA1), and (iii) soybean in bi-annual rotation with maize under conservation agriculture (CA2). Several cover/relay crops were associated prior to and with the main crops. Soil sampling was conducted in 2011 and 2013 at 0-5, 5-10, 10-20, and 20-40 cm depths. Biomass-C inputs ranged from 2.2 to 7.8 Mg C ha-1 yr-1 under CT and CA respectively, emphasizing the difference of supply of fresh organic matter. On average, CA increased SOC and STN stocks at 0-5 cm depth by 20% and 25% when compared with CT. β-glucosidase and arylsulfatase activities at 0-5 cm depth was 28% and 36% greater in CA1 and CA2 soils. In addition, CA2 (rotational sequence and higher biomass-C inputs) showed a better increasing trend of labile C fraction (HWEOC and POXC) and β-glucosidase and arylsulfatase activities than CA1. Conservation agriculture shows potential for the long term improvement of Cambodia uplands. (Texte intégral)

The continuous use of plowing for grain production has been the principal cause of soil degradation. This project was formulated on the hypothesis that the intensification of cropping systems by increasing biomass-C input and its biodiversity under no-till (NT) drives soil restoration of degraded agro-ecosystem. The present study conducted at subtropical [Ponta Grossa (PG) site] and tropical regions [Lucas do Rio Verde, MT (LRV) site] in Brazil aimed to (i) assess the impact of the continuous plow-based conventional tillage (CT) on soil organic carbon (SOC) stock vis-à-vis native vegetation (NV) as baseline; (ii) compare SOC balance among CT, NT cropping systems, and NV; and (iii) evaluate the redistribution of SOC stock in soil profile in relation to soil resilience. The continuous CT decreased the SOC stock by 0_58 and 0_67MgCha_1 y_1 in the 0- to 20-cm depth at the PG and LRV sites, respectively, and the rate of SOC sequestration was 0_59 for the PG site and ranged from 0_48 to 1_30MgCha_1 y_1 for the LRV site. The fraction of C input by crop residues converted into SOC stock was ~14_2%at the PGsite and ~20_5% at the LRV site. The SOC resilience index ranged from 0_29 to 0_79, and it increased with the increase in the C input among the NT systems and the SOC sequestration rates at the LRV site. These data support the hypothesis that NT cropping systems with high C input have a large potential to reverse the process of soil degradation and SOC decline. (Résumé d'auteur)

La connaissance des différentes unités agronomiques au niveau d'un terroir et leur utilisation par les agriculteurs est indispensable si l'on veut adapter les propositions de systèmes SCV aux contraintes du milieu. Ces unités agronomiques sont définies de manière à constituer des ensembles homogènes, pour lesquels les systèmes de cultures que l'ont peut proposer sont identiques. Ainsi, l'origine d'un sol n'est pas vraiment discriminante (il ne s'agit pas d'unités pédologiques), mais on s'attache avant tout à prendre en compte les caractères discriminant les possibilités de culture. Dans la zone agro-écologique de moyenne altitude, avec longue saison sèche, la différenciation agronomique des sols se fait sur la base de leur niveau de fertilité, de leur compaction, et de leur régime hydrique (en saison et en contre-saison). Ainsi, les pratiques agronomiques peuvent faire évoluer une parcelle d'une unité à une autre. Par exemple, un sol compacté sur lequel on installe des plantes de couvertures au système racinaire très puissant, peut ainsi évoluer en quelques années vers un sol non compacté. De même, la fertilité du sol peut évoluer, dans un sens ou dans un autre. En pratique, on peut distinguer ces unités en se basant sur la couleur du sol, la flore en place et les performances des cultures conduites par les paysans.