To date, information on the efficiency of nutrients applied as organic fertilizers is scarce. Apparent recovery of nutrients applied as cattle manure or as anacharis (Egeria densa) residues were compared. Large masses of anacharis are removed from the reservoirs of the Paulo Afonso hydroelectric power plant and the disposal has been problematic. A pot experiment was carried out with five consecutive corn crops of 45 days each, planted after a single dry matter application (doses of 0, 10 20, 30 and 40 Mg ha-1). Incorporations of anacharis and manure resulted in increased biomass yields and in N, P and K contents proportional to the applied doses. However, the effects of anacharis were 3-10 times higher than those of manure, except for the P content, which was similar. Gains in biomass with anacharis fertilization were observed during the first crop, while those of manure were observed only in the third crop. In the fifth crop the effects of both sources were small. The nutrient recovery was also higher for anacharis than for manure (N, 34-39 % and 7-22 %; P, 47-103 % and 9-11 %; K, 55-76 % and 26-34 %, respectively). But, for both fertilization types part of the nutrients remained in the soil and only a small proportion was taken up in the last crop. Anacharis supplies more nutrients and at a faster rate than manure and its use as organic fertilizer is worthwhile.
organic fertilizer; aquatic plant; incorporation to the soil; nutrients
