Weed management through short-term improved fallows in tropical agroecosystems

Weeds in tropical agricultural systems can cause serious economic damage, and their control often requires the commitment of substantial resources in the way of labor, capital, or pesticides. Tropical shifting cultivation systems employ a fallow period to help overcome weed infestations in addition to improving soil productivity and reducing other pest populations. Short-term, intensive fallow systems that employ herbaceous and woody species to facilitate rapid restoration of soil productivity have evolved as an alternative to long-term fallows. Short-term fallows can impact weeds at all growth stages and play a role in the integrated management of weeds and crops. Fallow management that promotes vegetative soil cover may reduce weed recruitment due to attenuation of soil temperature and/or shift in light quality at the soil surface. Residues or litterfall from fallow species may alter the chemical and microbial ecology of the soil to favor losses from the weed seed bank due to germination, loss of seed vigor, or seed decay. In addition, fallow vegetation can influence weed seed predation. Enhancement of soil productivity should increase the vigor of crop growth and enable crops to better compete with weeds. The burning of fallow species residues may result in weed seed death due to extreme temperatures or may induce seed germination by the release of mechanical dormancy or chemical germination cues. Certain weeds may serve as improved fallow species due to their high nutrient scavenging efficiency in low-fertility environments and their ease of establishment. Short-term improved fallows can be an important component of integrated weed management, particularly by promoting the prevention and tolerance of weeds in crops.