Mineral nutrition of Andropogon gayanus Kunth var. bisquamulatus (Hochst) Hack: IV. dry matter production, concentration of nutrients, and coefficient of digestibility

Abstract

This work deals with mineral nutrition of Andropogon gayanus var. bisquamulatus (Hochst) Hack. The following parameters were studied: weight of dry matter, concentration of macro nad micronutrients on plants from 20 to 140 days old, and the coefficient of digestitility of the dry matter in relation to the age of the grass. The plants were collected, at intervals, from 20 to 140 days old, from an area of half hectare of "Terra Roxa Estruturada", in Piracicaba, State of São Paulo, Brazil. The dry matter at 80 days was analysed for N, P, K, Ca, Mg, S, B, Cu, Fe, Mn, and Zn contents. The coefficient of digestibility was determined "in vivo" by using the nylon bag technique. It was observed that the coefficient of digestibility decreased with the aging of the grass, and at 80 days, which corresponds to the maximum production of dry matter (58,000 kg/ha), the coeficient of digestibility for leaves and stems was 71,27% and 66.47%, respectively. When plants were 80 days old the leaves presented the following concentrations of nutrients: N (1.46%), P (0.12%), K (1.79%), Ca (0.27%), Mg (0.16%), S (0.07%), B (11.75 ppm), Cu (4.75 ppm), Fe (236.75 ppm), Mn (74.50 ppm), and Zn (22.25 ppm).