INCIDÊNCIA DE ERVAS DANINHAS E ATRIBUTOS DO SOLO EM UM AGROSSISTEMA DA PRÉ-AMAZÔNIA, SOB EFEITO DA COBERTURA MORTA DE DIFERENTES COMBINAÇÕES DE LEGUMINOSAS EM ALÉIAS

In humid tropical land-use systems weed diversity and aggressiveness are extremely high, posing serious limitations to no-tillage agriculture. This paper investigates the effects of combining low- and high-quality organic residues on weed abundance and biomass and selected soil quality indicators. For this purpose, a field experiment was installed in January 2002 on-station at Maranhao State University, comprising four legume species: Leucaena leucocephala (Lam.) De Wit., Cajanus cajan (L.) Millsp, Clitoria fairchildiana R.A.Howard and Acacia mangium Willd., resulting in the following treatments in a completely randomized block design with 4 replications: L.leucocephala + C.cajan; A.mangium + C.cajan; C.fairchildiana + L.leucocephala; L.leucocephala + A.mangium and control (no legumes). Sampling was conducted in 2005 and 2007. We determined weed abundance and biomass, and N, P, K, Ca, lignin e polyphenol contents of the residues. In the topsoil we determined pH, the contents of organic matter, P, K, Ca, Mg, and H+Al, and soil density, total porosity and aeration capacity. We conclude that aggressiveness of weeds can be reduced and at the same time soil fertility can be improved with alley-cropping systems which contain the combination of both high- and low-quality residue producing plants.