Foram cultivados algodoeiros das variedades I. A. Campinas 817 e I. A. 7387-24940 durante 150 dias em soluções nutritivas, e mediante a análise periódica das soluções calculou-se a absorção dos elementos N, P, K, Ca, Mg, S e Fe, com o fim de se estabelecerem as épocas de maiores exigências em cada um, no ciclo vegetativo da planta. Os resultados mostram que o algodoeiro foi exigente em Mg, S e Fe logo nos primeiros 30 dias de vida. A absorção de N, P, K e Ca foi máxima na época do florescimento, isto é, entre o aparecimento das primeiras "orelhas" e a individualização das "maçãs", ou seja, dos 30 aos 60 dias do ciclo. Ao cabo dêste período tinham as plantas absorvido cêrca da metade do total de N, K, Ca e S retirados durante todo o tempo de duração do ensaio. Os resultados mostram, também, que ao se abrirem os primeiros frutos (120 dias) as plantas praticamente já haviam absorvido 90% do total de cada elemento estudado.
The amount of minerals absorbed by cotton plants (Gossypium hirsutum L.) was determined by chemical analysis of samples from the nutrient solutions in which they were growing, collected at ten-day intervals throughout fifteen decades. The results were as follows: (a) - in a general manner the bulk of absorption occurred between the 20th and 60th days for all nutrients; (b) - N-P-K uptoke was larger during the early square and early ball stages with a secondary peak observed 20 to 50 days after these stages; (c) - maximum Ca uptake occurred in the 20-50 day stage, with moderate uptakes at 70, 110, and 140 days; (d) - Mg absorption was higher in the first 10-50 days, and moderate afterwards; (e) - S uptake increased until the 50th day and decreased afterwards; (f) - Fe absorption was moderote at 10-20 and 45-80 day stages, and irregular outside these periods. Approximately 1/5 of the total Mg, S, and Fe was taken up during the first 30-day period in the life of the plant, ending with the formation of the first square. By the time setting of the first boll occurred (60 days), approximately 1/2 of the total N, K, Co, and S hod been taken up by the plant. Finally, at the opening of the first boll (120 days), 90 per cent of the total uptoke had been already absorbed by the plant, thus indicating that only 10 per cent was taken up during the final ripening and maturing period. The N, P, K, Ca, and Mg concentrations (not the weight per plant) decreased both in shoots ond roots from the beginning to the end of the vegetative cycle in nutrient solutions; Ca and Mg concentrations in roots remained almost constant, whereas Fe concentration in shoots and roots increased as the plants became older.
