Abstract: Small-scale African farmers typically have few resources for the management of weeds and soil fertility. Weed composition varies with soil properties and crops compete with weeds for available nutrients. We conducted field surveys in four districts to study the effects of cropping systems, fallow, landscape position, and soil characteristics on weed composition and evaluated the value of weed species density in predicting soil fertility conditions. Weed density was higher with annual than for banana-based cropping systems with higher relative densities of hairy beggarticks and garden spurge and lower relative densities for Cyperus spp. and johnsongrass in the banana-based systems. The relative densities of weed species varied with the length of the postfallow period, landscape position, drainage, and soil properties. Long-term rotation of annual and perennial cropping systems may be more effective than fallow in reducing total weed numbers, but fallow may be effectively used to reduce the relative densities of tropical spiderwort, Cyperus spp., and goosegrass. Relative densities of blue couch, goosegrass, garden spurge, Cyperus spp., oxalis, and johnsongrass varied more with nutrient supply than for other species. Soil properties had less effect on the distributions of tropic ageratum, hairy beggarticks, tropical spiderwort, and smallflower galinsoga. High relative densities of blue couch and garden spurge were generally associated with low soil nutrient levels. Goosegrass, johnsongrass, and oxalis were associated with higher nutrient levels. Information on the relationship of soil nutrient levels with weed flora was used to develop a decision guide to aid farmers in the identification of areas in their fields with severe nutrient deficiencies.
Nomenclature: Banana, Musa spp.; blue couch, Digitaria scalarum (Schweinf) Chiov #3 DIGSC; garden spurge, Euphorbia hirta L. # EPPHI; goosegrass, Eleusine indica (L.) Gaertn # ELEIN; hairy beggarticks, Bidens pilosa L. # BIDPI; johnsongrass, Sorghum halepense (L.) Pers. # SORHA; oxalis, Oxalis latifolia; smallflower galinsoga, Galinsoga parviflora Cav. # GASPA; tropic ageratum, Ageratum conyzoides # AGECO; tropical spiderwort, Commelina benghalensis L. # COMBE.
Additional index words: Banana, decision guides, indicator plants, relative density, soil fertility management, weed flora composition, weed management.
Abbreviation: RD, relative density.
