NITROGEN RETENTION IN RAPIDLY-GROWING STEERS GIVEN UREA SUPPLEMENTED DIETS

Résumé

"Shika" (indigenous, V,) and "Ngala" (introduction, V₂) varieties of elephant grass (Pennisetum  purpureum Schum.) field planted at 60 x 90, 60 x  60 or 60 x 30 cm spacing and fertilized at 0, 100,  200 or 400kg N/ha/yr, were examined for dry matTer (DM) yield, crude protein (CP) content, CP  yield, nitrogen (N) recovery and stand persistence at  Shika during the 1975 and 1976 growing seasons.  The highest DM yield resulted from 60 x 30 cm  spacing/400kg N combination but the 60 x 60 cm  spacing (27,800 plants/ha) with 200kg N appeared  optimum for yield. V produced 4.3 to 21.0t DM  and V₂ 2.8 to 17.41 DM/ha/yr over the range of  population densities and fertilizer levels investigated. DM yield per kg N applied rose with increasing population density (V, only) and decreasing  N rate, the highest value of 49kg being recorded for V _t. Mean herbage CP content varied from 7.0% without N to 9.7% with 400kg N/ha but the highest value of 11.0% was obtained from V₂ planted at 60 x 90cm. For both grasses, N increased annual CP yield 1.2— 4.5—Fold. The highest apparent fertilizer N recovery of 76.3% occurred at 200kg N/ha while plants survived best at 60 x 60cm spacing.