Management practices for biomass production of bioenergy grasses may differ
from management for forage. Our objective was to determine the yield and s
tand responses of 'Alamo' switchgrass (Panicum virgatum L,) to N and P fert
ilization as affected by row spacing. A combination of five rates each of N
and P were applied to plots during 1992 to 1998 at Stephenville. TX and 19
93 to 1995 at Beeville, TX. Three row-spacing treatments were applied as su
bplots. Biomass production was determined each year with a single harvest i
n late summer, Tiller density and tiller mass were measured during 1993 to
1996 at Stephenville, Biomass production was not influenced by the addition
of P, Biomass production response to N at Beeville was greater in narrow r
ows than wide rows during the establishment year only. Biomass production r
esponses to N were quadratic in 5 of 7 yr at Stephenville and linear at Bee
ville, A maximum yield of 22.5 Mg ha(-1) occurred during 1995 at Stephenvil
le at 168 kg N ha(-1), Lodging occurred at both locations but only at the 2
24 kg N ha(-1) rate. Tiller density and mass increased as row width increas
ed, Tiller mass also increased with increasing N fertility at Stephenville.
This response was more important in determining biomass production than wa
s tiller density, Average biomass production at 168 kg N ha(-1) yr(-1) was
14.5 and 10.7 Mg ha(-1) yr(-1) at Stephenville and Beeville, respectively,
Biomass production without applied N tended to decline over the years. Our
data indicated that switchgrass biomass production is sustainable at Stephe
nville only with the application of at least 168 kg N ha(-1) yr(-1) but P a
pplication and row spacing are not crucial.