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Vegetables in Cambodia are commonly sold in informal markets lacking food safety standards and controls. Currently, data on microbial contamination of vegetables in Cambodian informal markets are limited. The purpose of this study was to investigate Salmonella enterica and indicator organisms (generic Escherichia coli and coliforms) on the surface of fresh vegetables sold in informal markets in Cambodia. A sample of loose-leaf lettuce, tomatoes, and cucumbers were collected from 104 vendors at four informal markets in Battambang and Siem Reap provinces during rainy and dry seasons. Detection methods for Salmonella enterica were adapted from the Food and Drug Administration's Bacteriological Analytical Manual (FDA BAM). Quantification of coliforms and generic E. coli populations was conducted by plating onto E. coli/Coliform count plates. Salmonella enterica was most prevalent on lettuce during the dry season (56.5%, 95% CI [41.0, 70.8]) compared to the rainy season (15.4 95% CI [7.5, 29.1]), whereas no significant seasonal differences were apparent for tomatoes and cucumbers. Regardless of season, levels of Salmonella enterica were highest on lettuce (5.7 log CFU/g, 95% CI [5.5, 5.9]), relative to cucumbers (4.2 log CFU/g, 95% CI [3.8, 4.6]) and tomatoes (4.3 log CFU/g, 95% CI [4.1, 4.6]). For generic E. coli, prevalence was higher during the rainy season (34.0%, 95% CI [25.4, 43.8]) as compared to the dry season (9.1%, 95% CI [4.9, 16.5]), with the highest prevalence estimated on lettuce. Similarly, the level of coliforms on lettuce and tomatoes was greater during the rainy season (6.3 and 5.3 log CFU/g, 95% CI [5.7, 6.8] and [4.7, 5.8], respectively), relative to the dry season (5.2 and 3.9 log CFU/g, 95% CI [4.7, 5.7] and [3.4, 4.4], respectively). In summary, these results indicate seasonal patterns for microbial prevalence in lettuce, and an overall high level of bacterial contamination on raw vegetables sold in Cambodian informal markets.

Soil organic carbon (SOC) pools, particularly labile pools, and soil enzymes are good indicators of short-term impacts of soil management. We hypothesized that labile SOC pools drives C accumulation and enzyme activity can be an efficient indicator for C build up in short-term conservation agriculture. The aims of this study were to quantify the impacts of tillage and crop rotations with diverse crop residue inputs on changes in SOC labile pools and enzymatic activities in rice-, soybean- and cassava-based cropping systems designated as RcCS, SbCS and CsCS, respectively. The four treatments in each cropping system consisted of: conventional tillage (CT), no-till in which main crops (rice, soybean and cassava) were grown in a one-year frequency pattern (NT1) and, no-till in which the main crops were grown in bi-annual rotations with maize (NT2 and NT3). After 5 years experiment period, greater hot-water extractable organic C (HWEO-C) stocks of 61%, 55% and 53%, and permanganate oxidizable C (POX-C) stocks of 23%, 21% and 32% were attributed to NT than those in CT soils under RcCS, SbCS and CsCS, respectively, at 0–5 cm soil layer. The pyrophosphate extractable organic C (PEO-C) and chemically stabilized organic C (CSO-C) stocks were almost constant in each depth among treatments, except 0–5 cm in CsCS. The β-glucosidase activity was 18%, 28% and 49% greater in NT than those in CT soils at 0–5 cm under RcCS, SbCS, CsCS, respectively. Arylsulfatase activity was 36% and 39% greater in NT than in CT under SbCS and CsCS, respectively but no significant differences in RcCS. A strong and positive correlation (P

CONTEXT The Greater Mekong Subregion has been undergoing rapid agricultural transformation over the last decades, as traditional diverse subsistence-oriented agriculture is evolving towards intensified commercial production systems. Negative environmental impacts often include deforestation, nutrient pollution, and greenhouse gas (GHG) emissions. OBJECTIVE This study aims to explore the potential of crop-livestock integration to mitigate trade-offs between economic and environmental impacts of smallholder farming systems at different stages of agricultural transition and degrees of agricultural diversity across the Greater Mekong Subregion. METHODS We chose a ‘middle ground’ between detailed modeling of few, representative farming systems and modeling of large household populations. 24 low and high diversity farms were selected in Laos (Xieng Khouang province), Cambodia (Ratanakiri province) and Vietnam (Central Highlands) from a survey dataset of 1300 households. These farming systems were simulated with the whole-farm bio-economic and multi-objective optimization model FarmDESIGN, calculating operating profit, GHG emissions and nitrogen (N) balance. Two optimizations (‘business as usual’ vs. ‘crop-livestock integration’) were performed, generating ‘solution spaces’ or alternative configurations aiming to maximize profitability, keep farm N balanced and minimize GHG emissions. RESULTS AND CONCLUSIONS Agricultural systems across the sites differed in their production orientation and management practices, representing various stages of agricultural transition. Nitrogen balances varied between sites, being negative in Ratanakiri (average − 20.5 kg N ha−1 y−1) and Xieng Khouang (−36.5 kg N ha−1 y−1) and positive in the Central Highlands (73 kg N ha−1 y−1). Negative balances point to unsustainable mining of nutrients due to sale of cash crops without sufficient inputs, and positive balances to the risk of environmental contamination. Total GHG emissions ranged from 0.52–8.12 t CO2e ha−1 and were not significantly impacted by stage of agricultural transformation or agricultural diversity. GHG sources in Ratanakiri and Xieng Khouang were determined by crop residue burning while in Central Highlands fertilizer and livestock were main emitters. High diversity farms obtained higher operating profits (10,379 USD y−1) than low diversity farms (4584 USD y−1). Crop-livestock integration, a combination of measures including introduction of improved forages grasses, manure recycling and residue feeding, and reduction of residue burning, resulted in larger ‘solution spaces’, thus providing farmers with more options to mitigate agro-environmental trade-offs. SIGNIFICANCE These findings underline the potential of crop-livestock integration to support sustainable intensification pathways in the Greater Mekong region. Public and private investment in further research and extension is needed to develop and scal, Agricultural Systems, 195, ISSN:0308-521X

Rice is one of the most important agricultural commodities throughout the Mekong River Basin including the Tonle Sap Lake floodplains in Cambodia. Recent increases in hydropower dams along the Mekong River have likely altered the surface water hydrology impacting the arable areas and soil qualities for rice production in the Tonle Sap lowland. Along with the hydrological impacts, the region’s rice farming is facing a rapidly changing climate. It is critical to understand how the hydrological changes associated with dam development impact the region’s rice production in a changing climate. The aims of this study were to assess the impacts of recent increases in hydropower dams on the timing and areas of rice cropping in the Tonle Sap floodplains and to evaluate the effects of changing hydrology, rising temperature, and adaptive farming practices on rice productivity using a process-based rice crop model: ORYZA (v3). The effect of dams on arable areas for rice was identified by a remote-sensing method based on the PhenoRice algorithm for the period of 2001–2019 in two rice-growing provinces: Kampong Thom and Battambang. The PhenoRice method identified an increase in rice growing areas as well as shifts in both timing and location of rice cropping towards the sources of irrigation during the dry season since 2010. The ORYZA model simulated a substantial yield reduction with an increase of 2 °C in air temperature in the region. The model predicted that the rice productivity in the region is sensitive to soil organic carbon content which is expected to change with surface water hydrology. The model also predicted that region’s rice yield can increase by optimizing the timing and amount of N fertilization. The findings from this study highlight how hydrology, climate, and agronomic practices can interact to impact rice production in the Lower Mekong Region and provide insights for effective water management and agronomic practices to attain food security in the region in a changing climate.

Cambodia has made significant efforts to improve nutritional outcomes while demonstrating increasing interest in ensuring that food safety challenges do not negate these efforts. This integrative review examines food safety in Cambodia to identify areas where efforts, both existing and recommended, could focus to best limit Cambodians’ exposure to foodborne disease. The review considers: 1) documented foodborne disease outbreaks in Cambodia; 2) aggregated food safety research taking place in Cambodia; 3) current food safety regulatory structures in the country; and 4) gaps in food safety knowledge or practices. Lastly, the review proposes an framework to bridge food safety gaps through the integration of improved surveillance, targeted intervention research informed, and a comprehensive understanding of Cambodians motivations, opportunities, and capabilities to adopt food safety practices.

Soil organic carbon (SOC) sequestration was evaluated for several long-term rain-fed cropping systems for conservation agriculture (CA) and conservation tillage (CT) in Cambodia using the Environmental Policy Integrated Climate (EPIC) model. The mean crop yield, biomass and SOC stocks of four treatments and three replication in each primary cropping system (rice, soybean and cassava) were used for calibration and validation during the period 2009–2013. The CT and CA1 treatments were assigned to continuous cropping of primary crops. CA2 and CA3 treatments were assigned to rotated primary crops with maize. In all CA treatments, forage or legume cover crops were prior planted and intercropped with the primary crops to maintain full soil cover. The results show that EPIC successfully simulated crop yields, biomass, and SOC. However, the model tended to underestimate SOC in the CT treatments and overestimate SOC in the CA2 and CA3 treatments. Crop residue was found to highly influence SOC sequestration. Sediment loss in the CT treatments was found to be four times greater than CA treatments due to the CT tillage effects. The 20-year future simulations, using historical weather and automatically generated by EPIC, showed a decrease trend in SOC stocks in all CT treatments and an increase trend in most CA treatments, with the greatest increase for CA2 and CA3 treatments. Thus, the CA treatments in combination with the maize rotation were demonstrated to be more efficient to manage SOC sequestration over CA with one continuous primary crop.

No-till (NT) cropping systems have the potential to enhance soil aggregation, providing physical protection and soil C sequestration. The existence of discrepancies in the impact of tillage on soil aggregation and soil C sequestration warrants further studies, particularly for different crop rotations. We hypothesized the following: a) NT biannual crop rotations tend to be more effective in restoring large macroaggregation and the concentrations of soil organic C (SOC), total N and permanganate oxidizable C (POXC) associated with macroaggregates than NT systems with a one-year frequency pattern and conventional tillage (CT); b) the continuous biomass-C inputs via crop residues in large macroaggregates under NT tend to increase the proportion of aliphatic C than those under CT. Therefore, the objectives of this study were: (i) to assess changes in the aggregate size distribution and levels of aggregate-associated total SOC, total N and POXC and (ii) to characterize humic acid (HA) using 13C CP-MAS nuclear magnetic resonance (NMR) spectra of 8- to 19-mm soil aggregate size class in a reference vegetation (RV) and in rice-, soybean- and cassava-based cropping systems (RcCS, SbCS and CsCS, respectively) in a clayed Oxisol after tillage and crop rotation management. We evaluated four treatments in each cropping system: 1) CT, and 2) three NT systems in a randomized complete block design with three replicates. Soil aggregate samples were collected at depths of 0–5, 5–10 and 10–20 cm. The conversion of RV to agricultural land influenced the distribution of aggregate size classes, soil aggregation indices and aggregate-associated SOC, total N and POXC in the two surface layers. The formation of large macroaggregates (8–19 mm) dominated the aggregate size distribution with a relatively higher proportion under RV and NT than under CT. Across all soil depths, the proportions of the 8- to 19-mm aggregate size fraction were 59% (NV), 43% and 47% (RcCS), 45% and 53% (SbCS) and 34% and 37% (CsCS) for the CT and NT systems, respectively. Among the three NT systems, the biannual crop rotations in the three cropping systems (NT2-Rice, NT2-Soybean, NT2-Cassava; NT3-Rice, NT3-Soybean and NT3-Cassava) indicated better performance than the one-year frequency pattern in restoring large macroaggregation and the concentrations of SOC, total N and POXC associated with large macroaggregates. Additionally, in the surface (0–5 cm) and subsurface (10–20 cm) soil layers, the SbCS with a high rate (7.32 Mg C ha−1 year−1) and diversity [Pennisetum typhoides) (Pearl millet)/maize + Brachiaria ruziziensis (Brz), Stylosanthes guianensis (St)] of biomass-C inputs reached the highest levels of lability of SOC and POXC in the macroaggregate size classes of 0.25–0.5 and 8–19 mm, respectively. The CP-MAS 13C NMR measurement suggests that the continuous and high biomass-C inputs with diverse crop residues under NT, such as millet, maize, Brz, St and Crotalaria juncea, tended to increase the proportion of aliphatic C than under CT; an opposite trend was observed for aromatic C. 13C NMR revealed an advance caused by the association between the quantity and quality of C addition via cultural residues in the discrimination of the composition of C in the macroaggregation in the tropical region.

Conservation agriculture (CA) is an effective tool that is used to increase soil C sequestration and enhance soil quality and agronomic productivity. However, rigorous empirical evidence from Southeast Asia, particularly in the Cambodian agro-ecosystem, is still scarce. We hypothesized that high and diversified biomass-C inputs in CA might be the first step toward to increase SOC in the topsoil by creating the C flow to support C storage overtime. Thus, the aim of this study was to quantify the short-term (i.e., five year) impacts of soil management and cropping systems on soil organic C (SOC), soil total N (STN), particulate organic C (POC) and mineral-associated organic C (MAOC). There were three distinct experiments comprised of a combination of cover and main crops including rice-, soybean- and cassava-based cropping systems, hereafter designated as RcCS, SbCS and CsCS, respectively. The experimental plots were laid out in a randomized complete block design with three replicates. Soil management treatments included conventional tillage (CT) and no-till (NT) and a selected adjacent area of reference vegetation (RV). Soil sampling was conducted in 2011 and 2013 at seven depths (0–5, 5–10, 10–20, 20–40, 40–60, 60–80 and 80–100 cm). Soil management and crop sequences significantly affected SOC and STN stocks in all three cropping systems. On average, NT SOC stocks at 0–5 cm depth was greater than those of CT by 10%, 20% and 18% and STN stocks by 8%, 25% and 16% for RcCS, SbCS and CsCS, respectively. SOC levels followed the order RV > NT > CT. SOC stocks in the subsoil layers were consistently lower in NT than in CT in all three cropping systems. POC stocks at 0–5 cm depth in NT were on average 22%, 20% and 78% greater than those in CT in RcCS, SbCS and CsCS, respectively. However, significant differences were detected only in RcCS and CsCS. The major POC stocks were found at 0–20 cm depth. NT treatments in SbCS stored 9% greater MAOC stocks at 0–5 cm depth than those in CT, and an increasing trend of NT was observed in RcCS and CsCS. In all three cropping systems, NT systems with diversified crop species significantly increased SOC stocks ranging by 6 to 28% and POC stocks by 56–127% in the surface soils and tended to restore SOC and POC in the subsoil layers after five years. The results leads to accept the hypothesis that short-term CA associated with high biomass-C inputs (particularly bi-annual rotations) promotes SOC recovery in the topsoil layer and creates a potential to increase SOC in the subsoil layers when deep-rooting cover crops are included in crop rotations.