Composição química do feijoeiro e absorção de elementos nutritivos, do florescimento à maturação

Abstract

Procedeu-se a um estudo das curvas de produção de matéria sêca, concentração e absorção de elementos minerais, no feijoeiro. Plantas da variedade Chumbinho opaco, crescendo nas condições de campo, com e sem adubação, foram colhidas em diferentes estádios do ciclo, a partir do florescimento. Dividiram-se as amostras em raiz, haste, fôlha e fruto, submetendo-as à análise quantitativa de N, P, K, Ca, Mg e S. Na planta madura, as sementes foram colhidas e analisadas separadamente da vagem. São também discutidos os efeitos provocados pela adubação sôbre aquelas características e a extração de nutrientes do solo pelo feijoeiro, na colheita, levando-se em conta o retôrno ou não dos resíduos de cultura. Os dados oferecem, ainda, indicações quanto à aplicação tardia de nitrogênio no feijoeiro, com base no fato de que uma absorção ativa de nitrogênio pela planta ocorre durante o período critico de crescimento das sementes, quando se intensifica a produção de carbohidratos. Nesta fase, a demanda da planta poderia não ser satisfeita à custa exclusiva do N fixado pelo processo simbiótico.

Nutrient extraction and exportation by common bean cultivars under different fertilization levels: I - macronutrients

“…Regardless of the treatment, it was observed that N, K and Ca were the nutrients accumulated in larger amounts in the stem, which was similar to results obtained by Gallo & Miyasaka (1961) and Cobra Netto et al (1971) in studies with common bean.…”

“…During most of the cycle, the treatments with 100 % of recommended NPK fertilization accumulated the largest amounts of macronutrient in the leaves, and the lowest amounts were observed in treatments without fertilization (Figures 2b, 3b, 4b, 5b, 6b, and 7b), which is similar to results given by Gallo & Miyasaka (1961). In treatments PD1 and AD1, the amounts of macronutrient accumulated in leaves were intermediate, but showed no significant difference from unfertilized treatments during most of the cycle, and from treatments with 100 % of recommended NPK fertilization during the vegetative stage.…”

“…However, a reduction in the amount of Ca accumulated in the leaves at the end of the cycle was especially due to leaf senescence and abscission (Figure 1b), since Ca remobilization in plant tissue is low (Malavolta et al, 1997), and the amount of this nutrient in reproductive structures increased slightly at the end of the cycle (Figure 5b,c). A reduction in the amounts of N, P, K, Mg, and S accumulated in leaves of common bean during grain filling was observed by Gallo & Miyasaka (1961), who attributed this behavior to the mobilization of nutrients from other plant parts to the reproductive structures. However, these authors also observed a decrease in the amount of Ca accumulated in the leaves, but only in a stage nearer the end of the cycle, showing that this decrease was due to leaf senescence.…”

“…Nevertheless, literature information on nutrient absorption by this crop is old, i.e., it was obtained in the 1960's and 1970's in situations where grain yield was lower than 1,000 kg ha -1 (Gallo & Miyasaka, 1961;Haag et al, 1967;Cobra Netto et al, 1971). …”

“…It is therefore possible that the nutritional requirements of the current common bean cultivars are not the same as those used in the 1960's and 1970's, the period in which nutrient absorption by common bean was studied and described in the literature (Gallo & Miyasaka, 1961;Haag et al, 1967;Cobra Netto et al, 1971).…”