Tandis que les zones de montagne moins peuplées apportent les ressources en eau qui permettent aux plaines de prospérer, les habitants des zones montagneuses continuent à souffrir de pauvreté, de faibles productivités agricoles accompagnées de dégradation environnementale. Une solution à ce paradigme semble être la mobilisation mutuelle de toutes parties prenantes via des mécanismes incitatifs de type PES (Payment for Environmental Services). L'idée est de relier politiques agricoles et stratégies individuelles dans une même action répondant aux contraintes physiques, économiques et culturelles des milieux physiques et humains en même temps qu'aux contraintes institutionnelles pour une bonne gouvernance. Un meilleur lien entre terres de pente et plaines devrait garantir un usage durable des terres de pente sans risque pour les plaines.

A research project was carried out in two areas in the outskirts of Hanoi city using a combination of qualitative and quantitative methods. The objective was to study interactions among the vegetable farming systems and the peri-urban context within which they are situated. The farms studied were characterised as small-scale farms that use high inputs of soil amendments and pesticides for diversified crop rotation systems. The main source of irrigation water and nutrients for vegetable farming in southern Hanoi is wastewater from the To Lich River. In northern Hanoi, irrigation water is obtained directly from the Red River and nutrients are supplied through high fertiliser inputs. The concentrations of COD (144 -287 mg l 21 ), N-NH 4 1 (1 -25 mg l 21 ), PO 4 32 (0.5-4 mg l 21 ) and coliform (525 3 10 3 -28 3 10 6 MPN 100 ml 21 ) along the To Lich River was much higher than the limits specified in the Vietnamese standard for water used in agriculture. A higher Cu content in soil in Phuc Ly seems to be linked to the high input of chicken manure at the site. However, the contents of heavy metals in irrigation water, in vegetables and in the soil surface layer at the two sites were lower than the Vietnamese maximum permissible levels.

Most agricultural production in central Vietnam relies on sandy soils distributed along the sea coast. Because of their low exchangeable potassium (K) and low cation exchange capacity (CEC), careful adjustment of K fertilization on these soils is needed to minimize K leaching. Quantity/intensity curves were established on 24 sandy soils from Thua Thien Hue Province from which K buffering capacity (PBC) was calculated and compared with basic soil properties. Potassium buffering capacity was found to correlate best with soil texture and only a little with humus content, although these two characteristics are responsible for CEC. A simple equation based on sand content, which is easier to determine than clay content, is proposed to calculate optimum exchangeable K level as a function of target K level in soil solution.