Institute of Technology of Cambodia

Research on the effects of rice fertigation using treated municipal wastewater (TWW) as the sole source of nutrients and irrigation water remains limited. This study examined the impact of continuous TWW irrigation on rice-soil systems across three years (2021-2023), focusing on soil health, plant growth and yield, and the mineral and toxic element composition of rice grains. Forage rice cultivation using TWW fertigation (test field) was compared with conventional cultivation using chemical fertilisers and canal water (control field). The test field exhibited an average total nitrogen (TN) removal rate of 72 % across three crop seasons. However, low TN concentrations in TWW (2021: 4.7 mg L^-1, 2022: 9.9 mg L^-1, 2023: 2.8 mg L^-1) resulted in lower leaf greenness, plant height, and shoot biomass compared to the control, particularly in 2023 (p < 0.01). In the same year, rice protein content in the test field (5.9 %) was significantly lower than the control (6.5 %) (p < 0.001), while mineral compositions remained consistent across fields (p > 0.05). Significant increases in K, Mg, Na, and Zn concentrations were observed in rice grains from the test field in 2021 (p < 0.05). However, As levels in the test field grains (0.35 mg kg^-1) in 2023 approached the maximum allowable limit and were significantly higher than that in the control (0.25 mg kg^-1), raising food safety concerns. TWW irrigation maintained soil C levels, with the test field exhibiting higher C:N ratios, humification indices, and complex carbon structures (R_ET:Bz and SUVA₂₅₄) across the three seasons. These improvements enhanced soil structure and nutrient retention. While TWW irrigation shows potential as sustainable alternative to chemical fertilisers, optimizing its application to address varying N concentrations and complex organic matter dynamics is essential to maximize productivity and ensure food safety and environmental sustainability.

Rivers are primary vectors of plastic debris to oceans, but sources, transport mechanisms, and fate of fluvial microplastics (<5 mm) remain poorly understood, impeding accurate predictions of microplastic flux, ecological risk and socio-economic impacts. We report on microplastic concentrations, characteristics and dynamics in the Mekong River, one of the world's largest and polluting rivers, in Cambodia and Vietnam. Sampling throughout the water column at multiple localities detected an average of 24 microplastics m^-3 (0.073 mg l^-1). Concentrations increased downstream from rural Kampi, Cambodia (344 km from river mouth; 2 microplastics m^-3, 0.006 mg l^-1), to Can Tho, Vietnam (83 km from river mouth; 64 microplastics m^-3, 0.182 mg l^-1) with most microplastics being fibres (53 %), followed by fragments (44 %) and the most common polymer being polyethylene terephthalate (PET) or polyester. Pathways of microplastic pollution are expected to be from urban wastewater highlighting the need for improved wastewater treatment in this region. On average, 86 % of microplastics are transported within the water column and consequently we identified an optimum sampling depth capturing a representative flux value, highlighting that sampling only the water surface substantially biases microplastic concentration predictions. Additionally, microplastic abundance does not linearly follow discharge changes during annual monsoonal floods or mirror siliciclastic sediment transport, as microplastic concentrations decrease rapidly during higher monsoon flows. The findings reveal complex microplastic transport in large rivers and call for improved sampling methods and predictive models to better assess environmental risk and guide policy.

This study is the first attempt to assess rice cultivation under alternate wetting and drying (AWD) and continuous flooding (CF) using the latest scenarios from the Intergovernmental Panel on Climate Change (IPCC), utilizing AquaCrop Model. Field experiments were conducted during the dry season 2023 to get the model calibration and validation input. We used two shared socioeconomic pathways scenarios (SSP3-7.0 and SSP5-8.5) developed within Coupled Model Intercomparison Project Phase 6 (CMIP6) and projected the rice growth during 2040-2070. The simulation results demonstrated the effectiveness of AquaCrop in capturing crop development across treatments and varieties. This model's accuracy in simulating canopy cover (nRMSE = 14-32.5%), time series biomass (nRMSE = 22-42.5%), grain yield (Pd = 4.36-24.38%), and total biomass (nRMSE = 0.39-18.98%) was generally acceptable. The analysis of future climate shows an increasing trend in the monthly average temperature by 0.8 °C (Tmin) and 1.3 °C (Tmax) in both scenarios. While ETo values were not anticipated, rainfall was expected to increase with average values of 5.62 mm to 11.25 mm. In addition, the study found that varieties with growing periods longer than 93 days after transplanting (DAT), such as CAR15 and Sen Kra Ob, were most impacted by heat stress conditions, leading to reduced yield, harvest index (HI), and water use efficiency (WUE). In our case, CAR15 and Sen Kra Ob grain yields were reduced by 53% and 8%, respectively. AWD maintains superior WUE compared with CF regardless of the type of varieties, suggesting this technique is a drought-adaptive strategy.