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The mountains of northern Vietnam have lost significant forest cover during the last decades due to the conversion from natural vegetation to cultivated land, leading to the depletion of soil organic matter and land degradation. The study evaluated bamboo as an alternative cropping strategy in the northern central upland of Vietnam. We analyzed above-ground carbon fixing capacity of bamboo, accumulation of soil organic carbon, and socio-economic aspects as compared to other land use systems. Over the long term, a bamboo-based cropping system compared favorably to several other land use alternatives in the area. Compared to cassava, rice and maize, bamboo provides 49–89% higher average return to labor. Carbon content in bamboo's standing above-ground biomass is 17 tons ha−1, 18% of that of forest. The soil organic carbon pool under bamboo amounts to 92 tons ha−1 to 70 cm depth, comparable to both forest and regenerated forest and 20% higher than land cultivated with cassava or maize. The study reveals that a shift in land use from annual crops to bamboo provides an annual net gain of soil organic carbon of approximately 0.44 tons ha−1. Such a shift is constrained however by income insecurity in the early stages of plantation, because bamboo takes 3–4 years to mature and has a low return-per-area basis compared to annual cash crops. The study suggests that a crucial incentive for farmers shifting to bamboo production may be to create alternative off-farm income-generating activities which absorb the labor liberated by the labor extensive farming of bamboo.

Vermicompost and biochar amendments are management practices which may contribute to sustainable agroecosystems by reducing dependence on inorganic fertilizers. However, little is known about their impacts on soil microorganisms and their transfer and evolution in connected aquatic systems. The aim of this study was to determine the influence of organic manure (buffalo manure, compost or vermicompost) and biochar amendments on bacterial and viral properties in soil and water. A three year experiment was carried out with terrestrial mesocosms which were used to test the effect of organic matter amendment on maize growth. In the last year of the experiment, runoff and infiltration waters from the terrestrial mesocosms were transferred to aquatic mesocosms. Organic fertilization improved soil properties (higher C, N content and pH H 2 O ) and as a consequence increased soil bacterial and viral abundance. Bacterial diversity (Shannon ‘H’ and richness ‘S’ indices calculated from DGGE fingerprint) was also enhanced after the continuous application of organic amendments. Compared with compost, vermicompost reduced viral abundance and S but similar H and bacterial abundance were observed. The pH H 2 O , C content and bacterial and viral abundance increased in the aquatic mesocosms following organic fertilization. As a consequence, bacterial and viral diversity also increased in the water, although no differences were found between compost and vermicompost. Biochar increased soil bacterial abundance for the mineral fertilizer treatment but did not influence bacterial and viral abundance in water. However, the combination of biochar and vermicompost led to an increase of viruses in soil and a reduction of bacteria in water. Similarity dendrograms from the DGGE banding patterns showed that the structure of bacterial communities was mainly influenced by the fertilizer treatments in soil but by the presence of biochar in water. In conclusion, this study demonstrated that the nature of the organic amendment has important consequences on both soil and water microbial abundance and diversity.