Accumulation and distribution of dry matter and nutrients during a 12-month growth cycle of cassava

Abstract

Abstract Two cassava (Manihot esculenta Crantz.) cultivars were planted in fertilized and non-fertilized plots to determine the accumulation and distribution of dry matter and nutrients in the plant and the effect on soil fertility. At monthly intervals eight plants were harvested and separated into four parts, the upper, middle and lower thirds of the aerial growth, and the roots, while each aerial part was divided into leafblades, petioles, and stem. These samples were analyzed for dry matter (DM) and nutrient content. Soil samples were also taken at monthly intervals and analyzed. Results indicated that in cassava DM accumulation was slow during the first 2 months, increased rapidly during the next 4 months and slowed down during the final 6 months as DM production was partly offset by leaf fall. At harvest (12 months) DM was present mainly in roots, followed by stem, leaves and petioles. Nutrient concentrations varied between plant parts and with the age of both the tissue and the plant. The concentration of most nutrients was highest between 2 and 3 months and then declined. Each nutrient had its own particular concentration profile within the plant. Thus, N, P and S concentrations tended to be high in the leaves, while those of K, Ca and Mg were high in petioles and stem; the Mn concentration was particularly high in petioles, whereas Fe concentration was low in petioles but high in roots. B and Cu were evently distributed within the plant. Most nutrients accumulated initially in leaves and stem, but were translocated to roots in the latter part of the growth cycle. Only Ca, Mg and Mn accumulated more in stems than roots. Removal of accumulated nutrients in the root harvest can seriously deplete nutrient reserves in the soil, particularly that of K, and to a lesser extent for N. Soil pH, exchangeable Al, Ca, Mg as well as available P were not greatly affected by plant growth, while exchangeable K decreased markedly during the crop cycle.