EFEITO ALELOPÁTICO DE PLANTAS DE COBERTURA, NA SUPERFÍCIE OU INCORPORADAS AO SOLO, NO CONTROLE DE PICÃO-PRETO

Under natural conditions, or at least when substract is the soil, allelochemical effects can suffer modifications if cover plants are maintained on surface or incorporated to soil. Levels of straw of cover plants, incorporated or not to soil, on emergence and initial development of Bidens sp. were evaluated. Experimental design consisted of randomized complete blocks with 4 replications and treatments arranged in factorial scheme where: A)- management of cover plants (incorporated or not); B)- cover cultivations (Brassica napus, Raphanus sativus, Trifolium vesiculosum and Lolium multiflorum) and C)- levels of straw (0, 1, 2, 4, 6 and 10 t ha-1). Straw of Raphanus sativus and Brassica napus determine, in general, greater reduction of Bidens sp growth. Straw on soil surface, reduces growth of Bidens sp., compared to its incorporation, being necessary at least 6 t ha-1 of straw. Cover plants straw incorporation, generally, stimulates growth of Bidens sp.