THE FALLOW PERIOD AS A WEED-BREAK IN SHIFTING CULTIVATION (TROPICAL WET FORESTS)

In the wet tropics weeds can grow all year round. In shifting cultivation systems the fallow period is used to restrain the development of weeds because they threaten the re-use of the land. Overhead shade suppresses the heliophytic weeds growing on the site and interrupts the continuous re-seeding of the field. This is the first phase of weed suppression. During the second phase, shade cover is maintained to allow the reduction of viable weed seeds in the soil. In the Tai farm system, Cote d'Ivoire, little weeding is carried out because optimum use is made of the natural fallow vegetation as a weed-break. The first phase took 6-12 months, the second 10 years. The shading out of weeds is cheap and effective yet demands much land. Those farm systems under the pressure of land shortage are likely to be infested by weeds. They suffer from weeds because shade-producing plants are eliminated from the system. Intensive use of the land is sometimes possible when shade plants are preserved (as stumps, tubers) during the period the field is covered by heliophytic crops, and are allowed to grow out afterwards.