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Cambodia has faced drastic agrarian changes over the last twenty years with a rapid and massive transformation of the uplands from forest into arable land. Soil quality depletion is one of the main drivers of the resulting decline in crop productivity and increasing production costs in the uplands of Battambang province. The objective of the study was to assess the early effects of conventional plough-based (20 cm) management (CT) and two conservation agriculture-based (CA) cropping systems (the use of a single—CAS vs. multiple cover crop species—CAM) on a maize monocropping system using three soil organic carbon (SOC) fractions on Mollisols in Battambang province. SOC content, permanganate oxidizable carbon (POXC) and soil CO2 basal respiration through SituResp® were recorded at a depth of 0–10 cm. Twelve sampling periods were used over the growth period of the cover crops and during the maize cycle. POXC and SituResp® were highly sensitive to management practices with, across the 12 sampling periods, higher values (p

This study quantified soil organic carbon (SOC) and soil total nitrogen (STN) changes in three long-term (14 years) experiments comparing conventional tillage (CT) and different no-till (NT) cropping systems using a diachronic approach and an equivalent soil mass approach. The three experiments were established in 2009 in a randomized complete block design with three replicates and comprise maize (MaiEx)-, soybean (SoyEx)-, and cassava (CasEx)-based cropping systems. Soil samples were collected in 2021, 10 years after the first sampling (2011), at 7 depths: 0–5, 5–10, 10–20, 20–40, 40–60, 60–80, and 80–100 cm. At 0–10 cm depth, NTs significantly increased SOC stock at a rate of 0.35, 0.51 and 0.73 Mg C ha-1 y-1 for CasEx, SoyEx and MaiEx, respectively. CT exhibited a positive trend only on CasEx with an accumulation rate of 0.14 Mg C ha-1 y-1 (0-10 cm). A significant SOC accumulation was observed under NT cropping systems for CasEX and MaiEx up to 60-80 and 80-100 cm depth, respectively. By contrast, STN stock significantly increased under NT cropping systems only at 0–5 cm depth with an accumulation rate of 13.9, 22.9 and 34.0 kg N ha-1 y-1 under CasEx, SoyEx and MaiEx, respectively. A depletion of N stocks was observed under CT and NT cropping systems at deeper soil layers. Over 10 years of time, SOC accumulation rate of NT, at 0-100 cm depth, reached 1.08 and 1.73 Mg C ha-1 yr-1 for CasEx and MaiEx, respectively while non-significant change was observed under NT SoyEx and CT of the three experiments. The findings suggest that long-term NT cropping systems with high amount of biomass-C inputs and crop rotation enhance SOC sequestration even at deeper soil layers. However, these results raise questions about the dynamics of N under NT cropping systems.

Agriculture in the Southeast Asia region has been changing from traditional subsistence farming to modern commercial farming practices at various rates and this has led to specialized commercialized farming with mechanization, intensive tillage, and increased agrochemical use. The use of high inputs and labor-saving technologies has resulted in serious land degradation and vulnerable to more frequent and severe climate impacts, particularly drought and flood. Conservation Agriculture has been introduced in the region for the last two decades to conserve, improve, and make more effective use of natural resources through the integrated management of available soil, water, and biological resources, combined with purchased external inputs. Significant benefits of CA have been observed and technically proved, but the adoption is still in very limited areas and mostly in research and demonstration plots. For wider adoption, understanding the constraints that hinder adoption and addressing for specific situations including intellectual, social, financial, biophysical, technical, and infrastructure constraints, or policy related support.

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 concept and methods to assess soil quality have been widely debated in the literature for the last twenty years. We developed a new framework to assess soil quality following an integrative approach based on the measurement of soil dynamic functions rather than stocks, namely Biofunctool®. Biofunctool® accounts for the interactions between soil physico-chemical properties and soil biological activity. It consists of twelve in-field, time- and cost- effective indicators to assess three main soil functions: carbon transformation, nutrient cycling and structure maintenance. Firstly, the capacity of Biofunctool® to assess the impact of land management on soil quality was validated through a reliability, redundancy and sensitivity analysis. The results over 250 sampling points in Thailand showed the relevance of each of the twelve indicators to assess soil functioning. Secondly, we applied Biofunctool® and aggregated the indicators in a Soil Quality Index that synthetize the impact of land management on soil quality. Biofunctool® was applied within various contexts (tree plantations, agroforestry, conservation agriculture etc.) and two cases study will be presented: i.) impacts of a disturbance gradient based on various land uses and rubber tree stands in Thailand ii.) impacts of conservation agriculture practices in Cambodia. The overall results proved that Biofunctool® index provides a synthetic soil functioning score that is sensitive to land management and is robust in various pedo-climatic contexts. Therefore, Biofunctool® is a reliable tool to assess the soil integrated functioning, i.e., soil quality, and could be included within larger environmental impact assessment frameworks.

This report is to complete the terms of reference of the project signed between General Directorate of Rubber (GDR/MAFF, Kingdom of Cambodia) and Cirad on 22 June 2018 and called “Implementing Good Agricultural Practices (GAP) in Cambodia for a Climate Smart Rubber Production: Training sessions”, under a funding provided by Agence Française de Développement (AFD). A seminar was organized by GDR from 19 to 22 June 2018 in GDR head office in Phnom Penh, followed by a visit of Cambodian Rubber Research Institute (CRRI) experimental station in Tboung Khmum Province on 23 June 2018. The document report addresses 5 terms of reference, as stated in the contract: • TOR1. A reminder of the definitions of the concepts of Good Agricultural Practices (GAP) and Climate Smart Agriculture (CSA). • TOR2. A reporting of the activities of Cirad in each area of expertise: Agro-socioeconomics (Dr Bénédicte Chambon), agrophysiology and agronomy (Dr Eric Gohet and Dr Régis Lacote), ecophysiology (Dr Yann Nouvellon), soil fertility management and crop diversification (Dr Florent Tivet), focusing mainly on capacity building in each area. • TOR3. A drafting of a GAP (Latex harvesting system) manual, understandable by farmers. • TOR4. Proposed supporting experimentation (managed by CRRI) • TOR5. Proposals for a long-term cooperation between the three partners of the project (GDR, CRRI and CIRAD) for tackling the adaptation of rubber cultivation to the different rubber cultivation areas of Cambodia, taking into account the diversity of socioeconomic contexts.