Converting marginal hardwood forest to grassland has the potential of
increasing economic output with livestock grazing. Nitrogen (N) manage
ment during conversion needs to be evaluated to minimize possible adve
rse effects on the environment. This study was conducted to determine
temporal changes in quantities of N and biomass within ecosystem compa
rtments after herbicide application in a mature post oak (Quercus stel
lata Wangenh.)-blackjack oak (Quercus marilandica Muenchh.) forest. Th
e 4 treatments evaluated included; 1) no brush kill with no grass over
seeding, 2) brush kill with no grass overseeding, 3) brush kill with c
ool-season grass overseeding, 'K-31' tall fescue (Festuca arundinacea
Schreb.), and 4) brush kill with warm-season grass overseeding, 'Plain
s' Old World bluestem [Bothriochloa ischaemum var. ischaemum (L.) Keng
.]. Excellent brush kill was accomplished with 2.2 kg a.i. ha(-1) tebu
thiuron hylethyl)-1,3,4-thiadiazol-2-yl]-N'N-dimethylurea) applied in
spring 1993. Total N was measured during a 21-month period (June 1993
to February 1995), in 15- x 25-m plots, within 8 compartments; soil (0
to 60 cm), roots (0 to 60 cm), litter, top growth of herbaceous plant
s, woody plants <2.5 cm in diameter, and leaves, branches, and boles f
rom trees >2.5 cm in diameter. Stored N in tall fescue forage was 6 to
7 times greater than in Old World bluestem or native vegetation by Ju
ne 1994 and was 2 times greater in October 1994 and February 1995. Abo
ve-ground biomass of tall fescue and Old World bluestem was not differ
ent in October 1994 or February 1995, but both were greater than nativ
e vegetation, Litter biomass and total N in litter decreased, especial
ly in the tall fescue overseeding treatment, Total N in the soil for a
l treatments averaged 5,100 kg ha(-1) and fluctuations were not detect
able among treatments. Total N changes in other compartments were not
observable or were minimal. Blush kill and overseeding with grass had
little influence on total N stored within the ecosystem for 21 months
after treatment. N was redistributed to the herbaceous biomass compart
ment and away from the litter compartment after herbicide application,
regardless of the overseeding treatment applied.