RELATIONSHIPS BETWEEN WEED COMMUNITY AND SOIL SEED BANK IN A TROPICAL AGROECOSYSTEM

The viable weed seed bank in a maize field was studied at Campinas, Sao Paulo, Brazil. In 1984 50 soil samples (49 cm(2)) were taken at depths of 0-2 cm, 5-7 cm and 15-17 cm. The 150 samples were kept in resistant plastic bags arranged as vases and watered daily. The number of viable seeds was determined by counting the emerging seedlings. A total of 195 seeds emerged from the samples, i.e. an estimated 2325 seeds m(-2). Ageratum conyzoides dominated the 20 species recorded in the seed bank community. Of the weed species occurring aboveground, 41% in 1983 and 39% in 1984 were found as seeds in the soil samples. In 1983, 70% of the seed bank species occurred in the flora, and 85% in 1984. Based on these relationships, the tendency for cultivated soils in the tropics to have smaller seed banks than in temperate regions is discussed.