Abstract

Fertilizers can be used to change competition relationships between crop and weed  by promoting crop species growth, since rival species has a differentiated response to nutrients. We aimed to evaluate weed dry mass accumulation when or not  NPK (nitrogen, phosphorus and potassium) fertilizers were applied to  cassava crop. Therefore, weed samples were collected every 35 days, from 35 to 525 days after cassava planting, by randomly throwing a 0.25 m² metal square (0.5 m × 0.5 m) within useful area of the plots with and without fertilization. After each thrown, it was removed weed shoot, separated by species, then counted and weighed to determine number of plants and shoot dry mass. Fertilization did not influenced the weed population during most part of the crop cycle; however, promoted greater weed dry mass accumulation in the second crop year, 350 days after planting. Panicum maximum, Brachiaria plantaginea, Sida rhombifolia, Pavonia cancellata, Setaria parviflora and Cynodon dactylon, which were the most abundant weeds, had different responses to fertilization. P. maximum and B. plantaginea have outstood because of their shoot dry mass increase of 41.59 and 36.25%, respectively, when comparing fertilized and non-fertilized treatments .

Key words: Manihot esculenta, weed community, biomass, fertilizers.