Locations (Map) and treatments (Table
1) consisted of N fertilizer rates ranging from 200 to 418 lb N/acre
in two adjacent blocks ,
with each trial including the UF-IFAS rate and the grower’s rate. In
some trials, intermediate rates were also included. The UF-IFAS rates
were created by changing the rate or composition of the hot mix.
Custom-made blends were used in each trial to keep constant the rates of
P, K and micronutrients. The trials represented the diversity of growing
conditions in Southwest Florida and included different varieties (mostly
‘Florida 47’, ‘Sebring’ and BHN), plant densities (in-row spacing of 18
to 26 inch between plants; 5 or 6 foot bed centers),
soil types, and
farm sizes (700 to 5,000 acres). All the tomato crops were grown using
polyethylene mulch (white/black), except for one on
silver, stakes and
methyl bromide was applied at different rates as a soil fumigant.
Cooperators prepared the beds, applied the bottom and hot mix, fumigated
the soil, and applied the polyethylene mulch, transplanted, pruned,
staked, irrigated (seepage and
drip irrigation) and provided pest and
disease control.
Pre-season
soil samples were collected from each field,
oven-dried, passed through a 20-mesh screen, and sent to the ARL/USTL
laboratory in Gainesville for routine analysis using the Mehlich-1
extraction. Soil pH was determined in a 1:2 dilution (v/v) with
distilled water. In seepage-irrigated fields, shallow
monitoring wells
were installed in each treatment to measure the depth of the water table
depth. Monitoring wells were constructed from a 4-ft long, 4-inch
diameter PVC pipe screened at the bottom 8 inch. A float was attached to
one end of a 0.75-inch PVC pipe to serve as the water level indicator.
The float-0.75 inch PVC pipe assembly floated freely inside the 4-inch
well. Permanent marks were made at every 1 inch to indicate the water
table depth below the plastic mulch bed. Weekly observations of the
ground water table depth were taken throughout the growing season. On 30
and 60 days after transplanting (DAT), the shoots of three tomato plants
(fruits removed) selected randomly in each treatment were collected and
oven dried at 65°C until constant weight to determine dry matter
accumulation. Beginning at first flower buds and continuing until third
harvest, fresh petiole sap NO3-N and K concentrations were measured
weekly using ion-specific meters (Cardy, Spectrum Technologies, Inc.,
Plainfield, IL). The number of plants showing symptoms of
Fusarium crown
rot (caused by Fusarium oxysporum f.sp. radicis-lycopersici) in each
harvest plot was counted weekly in trial 1 between 12 Jan. and 2 Feb.
Weekly counts of all
adult whiteflies (Bemisia argentifolii) were made
on 10 top fully expanded leaves from 10 randomly selected plants in 3
locations in each plot at four trials (replicates). Analysis of the mean
number of whiteflies counted in each plot over each 7-day interval was
accumulated to give an estimated value of whiteflies x days for each
plot. An analysis of variance (ANOVA) over all replicates (farms) was
conducted by considering only the highest and lowest N rate treatments
(designated “high” and “low”) for those farms where more than 2 rates
were tested.
Harvest was done by the project’s crew on at least six
plots in each treatment following commercial practices.
Harvest plots
contained 10 plants each, and were 15 to 22 ft long, and were clearly
marked to prevent unscheduled harvests by commercial crews. Marketable
tomatoes were
graded in the field according to USDA specifications of
number and weight of extra-large (5x6), large (6x6), and medium (6x7)
fruit. The number of plots harvested in experiment five was twelve.
There were no true replications, but within each field the within-plot
variability of yield components was compared to the across-plot
variability using ANOVA and mean separation using the Duncan’s Multiple
Range Test at the 5% level.
The economic section of this paper calculates a
monetary value for each fertilizer treatment for each farm site. The
values compare projected total revenues gained by fertilizer treatment
utilizing yield data and market prices reported at the date of each
harvest. The purpose of the economic calculations was not to document
actual losses or gains, but to illustrate some of the economic issues
associated with N fertilization decisions.
Southwest Florida tomato growers harvest mature-green
tomatoes in two market windows - fall/winter and early spring. It is
important to realize that grower prices for the fresh tomato are set on
a daily basis and are sensitive to total market supplies. Tomatoes
imported from Mexico, Europe and Canada, compete with those from
Southwest Florida for the same market windows.
