Absorption of macronutrients by centrosema (Centrosema pubescens Benth.), Siratro (Macroptilium atropurpureum cv. 'Siratro') and perennial soybean (Glycine wightii Willd.) grown under field conditions

Seeds of the legumes where sowed in an Alfisol (Terra Roxa Estruturada) well supplied in nutrients. In order to find out the concentrations of the macronutrients as well the total amounts of nutrients absorved by the legumes, plants were harvested from 21 days after germinated up to 147 days. The plants were divided into leaves and stems and analysed for N, P. K, Ca, Mg and S by conventional methods. Digestibility test "in vivo" was carried out for the differents stages of development of the legumes. The authors concluded: - Maximum dry matter production was obtained by perennial soybean plants, followed by centro and siratro, between 134 and 140 days. - The maximum velocity of growth happen at 83 and 91 days for the three species. - The highest concentration of potassium was found in the legumes. - The maximum aounts of macronutrients extracted by the legumes are: CENTRO PERENNIAL SOYBEAN SIRATRO - The digestibility test by the nylon bag techniques (dry matter) showed differences between the stems and leaves. - The digestibility increased with the age for centro and siratro. - For perennial soybean the minimum of digestibility at 74 days (33.2%) for the stems and at 88 days (30.2%) for the leaves. - After 42 days the digestibility increased up to the 147 days for centro and stratro. - At 147 days the digestibility of dry matter for perennial soybean was 58.9%, for siratro 56.5% and for centro 44%.