Fertilization of established bahiagrass pasture in Florida

 Sid Sumner, Wayne Wade, Jim Selph, Jerry Southwell, Vicky Hoge,
 Pat Hogue, Ed Jennings, Pat Miller, and Travis Seawright*


Introduction
 There are about 2.5 million acres of bahiagrass
pasture used for beef production in Florida. A
major expense of maintaining this resource is its
annual fertilization. Recognizing this expense, and
the importance of good fertilization practices, the
Florida Cattleman's Association recommended in
1985 that the University of Florida, IFAS, reevalu-
ate the fertilization needs of pasture grasses.
 A three-year research study conducted at the
Ona Agricultural Research and Education Center
in the early 1960s (McCaleb et al., 1966) showed
that bahiagrass yield was not increased by phos-
phate (P205) fertilization, and a response to potash
(K20) fertilization was not obtained at rates higher
than 24 pounds per acre (lb/A) annually, even with
120 lbs nitrogen (N)/A applied as a split applica-
tion. Based on soil test values reported in the
study, IFAS fertilizer recommendations called for
annual applications of 48 lb of P205 and 96 lb of
K20/A (Jones et al., 1974). Later modifications of
IFAS recommendations indicated that 40 lb P205
and 80 lb K20/A should have been applied annually
(Whitty et al., 1977).
 Research at the Beef Research Unit near Gaines-
ville (Blue, 1970) showed that around 70% of the P
applied to a limed Leon fine sand pasture over an
18-year period had remained in the surface soil.
Further study (Rodulfo and Blue, 1970) showed
that bahiagrass responded to added P205 when
grown in the surface horizon of a virgin soil, but did
not respond to P205 when grown in the surface
horizon of soil from previously-fertilized pasture.
 Considering evidence that the P205 and K20
requirements of bahiagrass need to be evaluated
under conditions present on commercial ranches
that have been in production for many years, a field
study was conducted with the following objectives:
1) to determine if bahiagrass pasture responds to


P2O, and K20 fertilization when N fertilization is
60 lb/A/yr, a rate commonly used by ranchers
(IFAS, 1986); and 2) to compare the response of
bahiagrass pasture when fertilized according to
IFAS standard recommendations based on soil tests
with the response of bahiagrass fertilized at lower
rates ofN, P205 and K20.

Field study methods
 In 1986, one site in each of nine south Florida
counties was selected. Site locations and descrip-
tions are presented in the appendix. Each site was
a bahiagrass pasture on which a cow/calf manage-
ment system had been in effect for more than 10
years. A site in Pasco County was discontinued
after the first year due to severe mole cricket
damage of the bahiagrass pasture.
 At each site, five 50 x 100 ft areas were selected
and assigned one of five fertilization treatments.
These were: 1) no fertilizer; 2) 60 lb N/A applied in
March; 3) 60 lb N, 45 lb P205 and 45 lb K20/A
applied in March; 4) 60 lb N/A applied in March
and 60 lb N/A applied again in September; and 5)
60 lb N, 90 lb P205 and 45 lb K20/A applied in
March and 60 lb N and 45 lb K20/A applied in
September. Nitrogen, phosphate, and potash were
applied as ammonium nitrate, superphosphate, and
potassium chloride, respectively. Treatment 5
represented University of Florida, IFAS standard
recommendations (Whitty et al, 1977) for fertilizing
bahiagrass pasture based on test of soil samples from
each site when the demonstration was initiated.
 Soil samples were obtained from each treatment
area immediately prior to fertilization in March
and September each year of the demonstration.
Each soil sample consisted of a composite of five 6-
inch deep cores from each treatment area. Soil
samples were analyzed for pH and for Mehlich-I
extractable P, K, calcium (Ca), zinc (Zn), copper
(Cu), magnesium (Mg), and manganese (Mn).


*The authors are county extension staff at Polk, Hillsborough, Desoto, Hardee, Okeechobee, Highlands, Pasco, and Manatee
Counties, respectively, and participants in the South Florida Beef-Forage Program, Cooperative Extension Service, IFAS, University
of Florida. Appreciation is also extended to R. J. Stephenson, G. Kidder, M. F. Cole, J. S. Brenneman, J. E. Rechcigl, and F. M. Pate
for assistance on this project.