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Inefficient use of irrigation water threatens coffee production in Vietnam, the second largest producer worldwide after Brazil. This paper examines the irrigation issues that constrain sustainable coffee production in Vietnam. The period from January to April is a crucial time in the growth of the coffee crop. It requires irrigation, because rainfall only provides 25% of the potential crop evapotranspiration demand. According to crop phenology, this period also requires induced water stress, because it coincides with breaking the dormancy of flower buds and initiation of cherry development, which is crucial for achieving high yield. This paper proposes an irrigation supply of 120 or 150 mm between January and April in a year preceded by good or average rainfall respectively, in November and December. This is equivalent to 364 or 456 liters/plant/round in 3 rounds/year, which is only 70% of the locally recommended level by the Ministry of Agriculture and Rural Development. Synchronizing this irrigation supply with the management of other inputs could increase average yield up to 4000 kg/ha, from the present level of 2400 kg/ha making coffee production both sustainable and economically viable. In order to achieve this, building capacity of farmers to follow the irrigation and input application schedules is crucial. [ABSTRACT FROM AUTHOR]

Acidic pollution can cause severe environmental consequences annually in coastal areas overlain with acid sulfate soils (ASS). A water quality model was used as an analytical tool for exploring the effects of water management options and other interventions on acidic pollution and salinity in Bac Lieu, a coastal province of the Mekong Delta. Fifty eight percent of the provincial area is covered by ASS, and more than three-fourths (approximately 175,000 ha) are used for brackish-water shrimp culture. Simulations of acid water propagation in the canal network indicate that the combination of opening the two main sluices along the East Sea of the study area at high tide for one day every week in May and June and widening the canals that connect these sluices to the West Sea allows for adequate saline water intake and minimizes the acidic pollution in the study area. On the other hand, canal dredging in the freshwater ASS area should be done properly as it can create severe acidic pollution. [Copyright &y& Elsevier]

By comparing the successful story of a hydrodynamic model (based on its contribution to policy changes, management options and livelihood improvement) with other modelling cases in the Mekong River Delta, five success factors are identified. These are (1) simulated phenomena relevant to and understandable by policy makers; (2) response to the needs of policy setting; (3) developed and handled by national modellers with direct links to the policy process; (4) availability of input data; and (5) long application history. These success factors provide higher opportunities for engaging modelling activities with policy setting. [ABSTRACT FROM AUTHOR]

Wood charcoal production provides affordable energy in many developing countries and has substantially contributed to the economy through the provision of rural incomes. In several countries, charcoal production leads to overexploitation of forests due to inefficiencies in processing. This study was undertaken in central Laos to (1) examine and document traditional charcoal production systems; (2) investigate the production capacity, recovery efficiencies and economic gains of existing traditional charcoal production methods; (3) characterize the chemical properties of wood charcoal and investigate the potential for soil restoration and (4) investigate local charcoal producers' perception on forest degradation and their species preferences. Through a socio-economic survey, a cost-based method for economic valuation was undertaken on a range of charcoal production methods currently being used. Laboratory chemical analyses were performed on wood charcoal samples. Results indicated that the traditional mud charcoal mound was used by the majority (82%) of charcoal producers. Total charcoal production per production cycle varied between 400 (produced from 2.7 m3 of wood) and 1600 kg (produced from 18 m3 of wood), with a mean of 938 kg (±120) for traditional mud charcoal mounds. The volume of the traditional mud charcoal mounds correlated positively and significantly with total charcoal production (R 2 = 0.45, p = 0.03), whereas correlated negatively and significantly with the recovery efficiency (R 2 = 0.58, p = 0.01). On average, the local producers receive a total net benefit of 457,272 Lao kip (USD 57.2) in 17 days. We also identified a rice husk mound method of charcoal production, which may not encourage further deforestation while producing rice husk biochar that can be used for soil restoration. Furthermore, we found that there are significant differences (p < 0.05) between the sampled wood charcoals in chemical properties, indicating that the potential of using wood charcoal for the restoration of degraded soils varies from charcoal to charcoal. [ABSTRACT FROM AUTHOR]

A crop growth simulation model was used to study the impact of climate change for the period 2010–2050 on water productivity of rainfed rice. In general, the results suggest that water productivity of rainfed rice may increase significantly in the upper basin in Laos and Thailand and may decrease in the lower basin in Cambodia and Vietnam. Significant net increases in water productivity can be achieved by applying simple adaptation options such as shifting the planting dates, applying supplementary irrigation, and increasing fertilizer inputs. [ABSTRACT FROM AUTHOR]

• New mapping framework for flood and salinity risks in rice production of deltas. • Maps on a) peak risk, b) time-sequenced risk, c) sustained risk, d) risk profiles. • Sustained flood risk in Mekong Delta affects 39% of total rice area. • Sustained salinity risk affects 44% of total rice area incl. 31% for > three months. • Different methods have pros and cons, but add up to comprehensive risk assessment. The rationale for mapping hydrological risks in the Mekong River Delta (MRD) is the large extent of flood-affected and salinity-affected areas that severely constrain rice production. This new study on risk mapping expands previous approaches in depth (resolutions of 300 × 300 m and 1 h) and width (combining different types of maps). Data obtained with a hydrological model have been evaluated through four different methods of mapping individual attributes of risks that collectively comprise a comprehensive risk assessment for rice production: 1) Peak risk maps: These maps show the maximum water heights in a high-water year and maximum salinity concentrations in a low-water year. 2) Time-sequenced risk maps: The article provides hyperlinks to videos that encompass time-sequenced maps for the critical periods of floods (July-December in daily intervals) and salinity (March-April in hourly intervals) for all provinces. 3) Sustained risk maps (for rice): This approach is based on clearly defined thresholds of flood and salinity risks considering the duration of risk exposure at a given location. We have set thresholds for water heights exceeding 0.4 m and salinity concentrations above 2 g/l for 7 consecutive days to define start and end dates of sustained risks for rice. 4) Risk profile maps (for rice): The data on sustained risk have been aggregated at province level to calculate the geographic coverage of risk areas as compared with the total rice area. The rice area exposed to sustained flood risks in the MRD comprises 39% of the total rice area, which can be further subdivided into 24% with long (>three months), 12% with moderate (1–3 months), and 3% with short (1–4 weeks) risk duration. Likewise, the salinity-prone rice area accounts for 44% of the total rice area and can be subdivided into 31% with long, 8% with medium, and 5% with short risk duration. Finally, we have discussed the pros and cons of these different risk mapping methods in view of required adaptation strategies for rice production to cope with rapidly changing environmental conditions. [ABSTRACT FROM AUTHOR]

This study investigated the impacts of organic- and clay-based soil amendments, and their combinations on crop water productivity (CWP) using maize as a test crop. On-station field trials were established over two consecutive years at the Naphok and Veunkham sites in Laos. At each site, 10 treatments were applied in a randomized complete block design with three replications. The treatments were control, rice husk biochar (10 t ha−1), bentonite clay (10 t ha−1), compost (4 t ha−1), clay-manure compost (10 t ha−1), rice husk biochar compost (10 t ha−1), bentonite clay + biochar, bentonite-clay + compost, biochar + compost, and bentonite clay + biochar + compost. All treatments were applied in 2011. Significant (p < 0.05) treatment effects in CWP and growing period evapotranspiration were determined. At Naphok, differences between the amended and control plots in CWP varied between 0.1 and 0.6 kg m−3in 2011 and from 0.1 to 0.4 kg m−3in 2012, whereas differences at Veunkham varied between 0.3 and 1.0 kg m−3in 2011 and from 0.05 to 0.29 kg m−3in 2012. At both sites, CWP in 2012 was significantly lower than 2011. Our results illustrate that organic- and clay-based soil amendments improve CWP, indicating that soil-based interventions could be suitable options for improving agricultural productivity. [ABSTRACT FROM PUBLISHER]

In the Lao People’s Democratic Republic (PDR), increasing food security remains a challenge since smallholder agricultural systems, which are the main source of food production, are under serious threat due to poor soil fertility and climate variability. This study was undertaken in Lao PDR to investigate the impacts of organic and clay-based soil amendments on maize yield, total nutrient uptake, and soil properties. Structured field experiments were established over two consecutive years (2011 and 2012) with maize as the test crop at the Veunkham and Naphok sites. Ten treatments were applied in a randomized complete block design with three replications. The treatments were control, rice husk biochar (applied at a rate of 10 t ha−1), bentonite clay (10 t ha−1), compost (4 t ha−1), clay-manure compost (10 t ha−1), rice husk biochar compost (10 t ha−1), and their combinations. All treatments were applied in 2011. Significant (p< 0.05) treatment effects in maize grain yields, total nutrient uptake, and soil properties were observed. At Veunkham, differences between the control and amended soils in yield ranged from 0.9 to 3.3 t ha−1in 2011 and from 0.2 to 1.3 t ha−1in 2012, whereas differences at Naphok varied between 0.2 and 2.2 t ha−1in 2011 and from 0.2 to 1.7 t ha−1in 2012. At both sites, in most of the treatments, yields in 2012 were significantly (p< 0.05) lower than 2011; this was attributed to a late season drought. Differences between the control and amended soils in yield can be attributed to the improvements in total N and P uptake, soil pH, exchangeable Ca++and Mg++, and cation-exchange capacity following the application of soil amendments. The results of this study confirm that the soil amendments under consideration can be effective in improving agricultural productivity, while improving key soil properties indicating that soil amendments could be an option for intensification of agricultural productivity. [ABSTRACT FROM AUTHOR]

Highlights: [•] Organic and clay-based soil amendments significantly improve maize yield. [•] Low-cost soil amendments were economically viable within the first cropping season. [•] The payback period lasts up to five years in soils with higher-cost amendments. [•] Maize yield revenues do not provide sufficient incentives to farmers to adopt higher-cost amendments. [•] Up scaling low-cost amendments could contribute to food security through sustainable intensification. [ABSTRACT FROM AUTHOR]