Most farming practices are detrimental to soil organic matter reserves, leading to a significant decrease in biological activity and an increased risk of erosion. Soil invertebrate populations (macrofauna) are also sharply reduced in annual crop systems. The role of macrofauna in pedological processes and in the regulation of microbial activity has been fully described (Lavelle et al., 1999). Some agroecological practices and especially plant covers straw mulch or perennial plants intercropped with annual crops can enhance the sustainability of tropical cropping systems (Séguy et al., 1996). This study was aimed at assessing the effects of two plant covers (greater bird's food trefoil, Lotus uliginosus, and oat, Avena sativa) on soil macrofauna populations in Réunion (Indian Ocean).

In the highlands of western Réunion, the abandonment of fallowing, the use of monocropping and crop rotations under bare soil conditions, and excessive application of pesticides has led to physical, chemical and biological soil degradation. The technical and socioeconomic performances of farms with geranium (Pelargonium x asperum) as main crop have been markedly affected by these trends. They have also had a detrimental effect on the environment already weakened by serious natural constraints. Cropping over plant covers could enhance the sustainability of such farms under these adverse conditions.

Dans les Hauts de l'Ouest de l'Ile de la Réunion, la culture du géranium rosat (Pelargonium x asperum) est confrontée à des problèmes de maintien de la fertilité des sols. L'abandon de la jachère, les pratiques culturales en sol nu (monoculture ou rotations) et une très forte sensibilité des andosols à l'érosion, ont abouti à la dégradation physique, chimique et biologique (macrofaune) des sols. Cette dégradation du milieu s'est traduite par une diminution sensible de la production en huile essentielle. Pour y remédier, des essais relatifs à l'utilisation des couvertures végétales ont été installés. Ces dernières ont été constituées à partir d'une biomasse soit importée (paille de canne à sucre, Saccharum officinarum) soit produite sur place à l'aide d'une espèce pérenne (Stenotaphrum secundatum.) cultivée en association avec le géranium. En comparaison avec la culture du géranium en sol nu, les résultats montrent une augmentation hautement significative de la production en biomasse aérienne du géranium ainsi qu'en essence obtenue après distillation. En parallèle, la biodiversité, la biomasse et la densité de la macrofaune du sol sont restaurées sous couvert végétal.

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.

Effects of DMC on micro and macrofauna biomass, on CO2 respiration

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

Petit résumé fait par l'Université de Kasetsart sur l'interaction de la faune du sol et de la microflore du sol avec les diverses couvertures du sol, et formation.

The role of soil fauna, especially macro fauna, in soil genesis processes is now well known (Ketterings et al, 1997, Caesar-Thon That and Cochran, 2000). Thus, soil macro- fauna and its activity can accurately reflect soil functioning: recent works showed a direct and proportional relationship between earthworms activity and vegetal growth. These changes in micro and macro-fauna populations, abundance, and diversity and the soil biological activity all follow the same trends: a rapid decrease upon cultivation with traditional systems, and a fast improvement when a vegetal cover is permanently kept on the soil and plants with strong root systems improve its structure. These evolutions are similar to trends in yield evolution under various cropping practices. DPPSC systems proved to be highly efficient in restoring biological activity and fauna diversity in degraded soils.