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Soil aggregation, water-holding capacity, and biological activity under no-till systems and cropping sequences in the Lao PDR

Tivet F., Tran Quoc H., Boyer J., Chabanne A., Inthavong C., Senephansiri S., Keodouangsy L., Chounlamountry T., Khamxaykhay C., Panyasiri K., Séguy L.. 2010. In : Chanphengxay Monthathip B. (ed.), Khamhung Anonth (ed.), Panysiri Khamkéo (ed.), Chabanne André (ed.), Julien Frédéric (ed.), Tran Quoc Hoa (ed.), Lienhard Pascal (ed.), Tivet Florent (ed.). Investing in sustainable agriculture : the case of conservation agriculture and direct seeding mulch-based cropping systems. Proceedings of the Regional Workshop held in Phonsavan, Xieng Khouang Province, Lao PDR, 28th October - 1st November 2008. Vientiane : Ministry of Agriculture and Forestry [Laos], p. 130-144. Regional Workshop on Conservation Agriculture, 2008-10-28/2008-11-01, Phonsavan (Laos, République démocratique populaire).

In the four southern districts (Kenthao, Paklay, Boten, and Thongmixay) of Xayabury province, the current cropping systems are based on cash crop production. Maize is the main crop under rainfed conditions and covers more than 30,000 ha in the region. Land preparation is based mainly on plowing, which degrades soil and destroys infrastructures (paddy fields and roads). These deteriorations result from growing pressure on agricultural systems and farmers' lack of access to affordable labour. This study sought to analyze soil aggregation, soil water-holding capacity, and soil biological activity under tillage and notillage conditions in relation to the cropping sequence. Three cropping sequences were investigated: 1. maize monoculture; 2. two-year rotational sequence, maize - rice bean; 3. two-year rotational sequence, maize + Brachiaria ruziziensis - rice bean.). Each year of the sequence was represented under no-till (NT) and tillage (CT) practices. Independent of depth, soil aggregation was greater under no-till conditions and enhanced by crop rotation and higher dry matter production (maize + B. ruziziensis / rice bean). Soil macrofauna, that is, the number of species and amount of biomass, was increased with no-till and the cropping sequence. Earthworms increased with no-till and for some cropping sequences amounted to more than 50% of the total macrofauna biomass. The cropping sequences produced a limited amount of dry matter. The main challenge was to increase biomass productivity (above-ground and below-ground) to recover ecosystem functions (recycling of nutrients, carbon sequestration, high biological activity, integrated weed and pest management, etc.) in a medium-term process (five years). Generating and adapting intensive cropping sequences (high production of aboveground and belowground biomass combined with a high diversity) under no-tillage systems with smallholders is an essential step in achieving long-term land sustainability, to obtain more reliable harvests and higher farm profits.

Mots-clés : non-travail du sol; zea mays; oryza; phaseolus; république démocratique populaire lao; agriculture de conservation

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