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Thị Trấn Thanh Lưu, Vietnam

Lacombe G.,International Water Management Institute IWMI | Ribolzi O.,University Paul Sabatier | De Rouw A.,University Pierre and Marie Curie | Pierret A.,IRD Montpellier | And 13 more authors.
Hydrology and Earth System Sciences | Year: 2016

The humid tropics are exposed to an unprecedented modernisation of agriculture involving rapid and mixed land-use changes with contrasted environmental impacts. Afforestation is often mentioned as an unambiguous solution for restoring ecosystem services and enhancing biodiversity. One consequence of afforestation is the alteration of streamflow variability which controls habitats, water resources, and flood risks. We demonstrate that afforestation by tree planting or by natural forest regeneration can induce opposite hydrological changes. An observatory including long-term field measurements of fine-scale land-use mosaics and of hydrometeorological variables has been operating in several headwater catchments in tropical southeast Asia since 2000. The GR2M water balance model, repeatedly calibrated over successive 1-year periods and used in simulation mode with the same year of rainfall input, allowed the hydrological effect of land-use change to be isolated from that of rainfall variability in two of these catchments in Laos and Vietnam. Visual inspection of hydrographs, correlation analyses, and trend detection tests allowed causality between land-use changes and changes in seasonal streamflow to be ascertained. In Laos, the combination of shifting cultivation system (alternation of rice and fallow) and the gradual increase of teak tree plantations replacing fallow led to intricate streamflow patterns: pluri-annual streamflow cycles induced by the shifting system, on top of a gradual streamflow increase over years caused by the spread of the plantations. In Vietnam, the abandonment of continuously cropped areas combined with patches of mix-trees plantations led to the natural re-growth of forest communities followed by a gradual drop in streamflow. Soil infiltrability controlled by surface crusting is the predominant process explaining why two modes of afforestation (natural regeneration vs. planting) led to opposite changes in streamflow regime. Given that commercial tree plantations will continue to expand in the humid tropics, careful consideration is needed before attributing to them positive effects on water and soil conservation. © 2016 Author(s).

Bao Le Q.,ETH Zurich | Scholz R.W.,ETH Zurich | Seidl R.,ETH Zurich | Vu Q.M.,ETH Zurich | And 3 more authors.
iEMSs 2012 - Managing Resources of a Limited Planet: Proceedings of the 6th Biennial Meeting of the International Environmental Modelling and Software Society | Year: 2012

Phosphorus (P) is a key nutrient for food production. However, excess P use, e.g. in form of inorganic fertilizer application, can lead to environmental pollution, biodiversity losses and low profitability. Continuous cultivation with underuse of P fertilizer results in low food productivity and soil degradation due to soil nutrient mining or soil erosion. The concern is most serious for smallholder farmers in developing countries whose food production and livelihood is tied directly to their access to and efficient use of P as key nutrient for plant growth. This paper introduces a multi-agent system modeling framework for assessing long-term impacts of integrated P nutrient management options on soil fertility, food productivity and profitability of smallholder agro-ecosystems in different geographic regions. We consider Vietnam's smallholder systems in the Red River Delta (P overuse, market-oriented) and in the Northwest Mountain Region (P underuse, subsistence) as case examples for the two contrasting P use regimes. The model is planned to be used for informing trade-offs between long-term benefits and costs driven by different P management strategies and policies in a multi-stakeholder discourse.

Vu M.Q.,ETH Zurich | Vu M.Q.,University of Bonn | Vu M.Q.,Soils and Fertilizers Research Institute SFRI | Le Q.B.,ETH Zurich | And 2 more authors.
International Geoscience and Remote Sensing Symposium (IGARSS) | Year: 2012

This study aims to identify and classify the geographic hotspots of human-induced land degradation in Vietnam. We used the long-term (1982-2006) trend of inter-annual NDVI, derived from AVHRR/NOAA imageries, as a proxy for the decline or improvement in biomass productivity on a national scale. By analyzing the temporal correlation between rainfall and NDVI time-series over the last 25 years, we identified areas showing human-induced productivity decline from those in which the degradation was driven by climate dynamics. Finally, we identified areal clusters of human-induced productivity degradation associated with different profiles of social-ecological factors, which can be considered in follow-up causal analyses. We found that about 63,900 km 2 of land (19% of the national land) showed a persistent decline in biomass productivity. The maximum degraded areas were found in the southeast, Mekong River Delta, north western mountains, and Central Highland. We identified concrete social-ecological types of degradation hotspots, which can guide follow-up land degradation studies at different levels. © 2012 IEEE.

Ngo P.T.,French National Center for Scientific Research | Rumpel C.,French National Center for Scientific Research | Dignac M.-F.,French National Center for Scientific Research | Billou D.,French National Center for Scientific Research | And 2 more authors.
Ecological Engineering | Year: 2011

The addition of composted buffalo manure may lead to qualitative and quantitative improvement of the organic matter content of degraded tropical agricultural soils in Northern Vietnam. The objectives of this study were to follow the biochemical changes occurring during composting of buffalo manure with and without earthworms during 3 months and to study the effect of the end products (compost and vermicompost) on soil biochemical parameters and plant growth after two months of incubation under controlled conditions in an open pot experiment. Our conceptual approach included characterisation of organic matter of the two composts before and after addition to soil by elemental, isotopic analysis and analytical pyrolysis and comparison with conventional fertilisation. We also analysed for lignin content and composition. Our results showed that composting in the presence of earthworms led to stronger transformation of buffalo manure than regular composting. Vermicompost was enriched in N-containing compounds and depleted in polysaccharides. It further contained stronger modified lignin compared to regular compost. In the bulk soil, the amendment of compost and vermicompost led to significant modification of the soil organic matter after 2 months of exposure to natural weather conditions. The lignin component of SOM was unaffected whatever the origin of the organic amendment. Compost and vermicompost amendments both enhanced aggregation and increased the amount of organic matter in water stable aggregates. However, vermicompost is preferable to compost due to its beneficial effect on plant growth, while having similar positive effects on quantity and quality of SOM. © 2010 Elsevier B.V.

Jouquet P.,IRD Montpellier | Maron P.-A.,University of Burgundy | Nowak V.,University of Burgundy | Tran Duc T.,Soils and Fertilizers Research Institute SFRI
Soil Biology and Biochemistry | Year: 2013

This study aimed at testing the capability of microbial community structure and abundance to be used as bioindicators of the origin of earthworm cast aggregates. Compact surface casts produced by Amynthas khami and surrounding aggregates lacking visible signs of biological activity (control) were left to disaggregate by natural rainfall and separated into four size classes (5-2, 2-0.5, 0.5-0.25 and <0.25 mm). The genetic structure and the abundance of the bacterial and fungal communities were characterized using B- and F-ARISA fingerprinting approach and quantitative PCR directly from DNA extracted from soil. Bacteria and to a lesser extent fungi were more abundant in casts than in control aggregates for all the size fractions. In addition, PCA carried out from B- and F-ARISA confirmed the different microbial properties between cast and control aggregates for all the aggregate size fractions. In conclusion, this study confirms the cryptic properties of earthworm casts when fragmented by the rain and the relevance of bacterial and fungal abundance and diversity as biological indicators of the origin of soil aggregates. © 2012 Elsevier Ltd.

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