Vegetable BMP Research - 2004-2005 Season: Introduction
With more than 20,000 acres planted each year in Collier and Hendry counties, Southwest
Florida is an important production area for winter fresh-market tomato (Lycopersicon
esculentum Mill.). Depending on market conditions, Southwest Florida tomato
production is estimated between $150 and $300 million. While polyethylene mulch,
raised beds, stakes and transplants are always used, tomatoes are grown at various
dates, plant densities, and irrigation methods. Planting dates range from late August
to mid-February which results in 15 to 21 week-long growing seasons, as compared
to 13 week-long-growing seasons for spring plantings in North Florida. Within-row
spacing ranges from 18 to 24 inches, and beds are spaced 5 to 6 ft apart. When tomatoes
are grown on soils that have a shallow impermeable layer (3 to 6 ft deep), seepage
irrigation may be used. Seepage irrigation consists of maintaining and managing
a water table perched on an impermeable layer found between 18 and 24 inches from
the top of the bed. Seepage irrigation is also used for frost protection by raising
the water table to the soil surface. When the impermeable layer is absent or interrupted,
seepage irrigation is replaced by drip irrigation. In some cases, “hybrid systems”
are used where seepage irrigation is used to supply crop water needs, and a drip
tape is placed under the bed to supply fertilizers.
Current UF-IFAS recommendations for N fertilization in tomato production in Florida
are based on 6-ft center-to-center bed spacing, 7,260 linear beds foot/planted acre,
and consists of a base and a supplemental rate. The stet-wide base rate is 200 lb/acre
for N (1A = 7,260 linear bed feet) and soil-test-based rate for P, K and micronutrients.
Supplemental fertilizer applications are recommended in addition to the base rate
under the following conditions: (1) after a leaching rain (defined as 3 inches in
3 days or 4 inches in 7 days), (2) under extended harvest season (when the crop
is grown and harvested for more than 13 weeks), or (3) when plant nutrient levels
(leaf or petiole) fall below the sufficiency range while a UF-IFAS recommended irrigation
method is followed. Supplemental applications are recommended once a situation develops,
not on a preventive basis.
Fertilization practices used in tomato production in Southwest Florida are linked
to irrigation practices. For tomato grown with seep irrigation, approximately 25%
of the fertilizer is broadcasted in the bed (bottom or cold mix). The rest of the
fertilizer is applied in one or two bands on the shoulders of the bed (hot mix).
Water rising by capillarity slowly dissolves the fertilizer band, which supplies
nutrients to the crop. All the fertilizer is applied pre-plant and is expected to
adequately supply plant nutritional needs throughout the season. Additional fertilizer
applications are sometimes made through the plastic using a fertilizer wheel. With
drip irrigation, typical fertilization practices consist of applying 25% of the
total N and K2O rates broadcast on the bed area, while 100% of P2O5
and micronutrients are applied pre-plant. The remaining 75% of both N and K2O
are injected through the drip tape. With both irrigation systems, fertilizer rates
used for tomato production in Southwest Florida are typically higher than those
recommended because growers believe that recommended rates are too low and current
recommendations do not provide enough flexibility to reflect the different growing
conditions found throughout Florida.
The ‘Water Quality/Quantity Best Management Practices for Florida Vegetables and
Agronomic Crop” manual was developed in 2001-2004 jointly by the Florida Department
of Agriculture and Consumer Services and UF-IFAS to reduce the environmental impact
of off-site movement of fertilizers (www.floridaagwaterpolicy.com).
BMPs are cultural practices that aim at maintaining productivity while reducing
the environmental impact of production. The BMP manual for vegetables should be
adopted by rule (5M-6) and by reference in 2005. While the BMP manual recognizes
several strategies for nutrient management (including fertilizer rates that exceed
current recommendations), the long-term success of this voluntary program is based
on the improvement of water quality. Although N runoff has not been identified as
a widespread problem in south Florida, the environmental concern remains that the
combination of over-fertilization and excessive irrigation may contribute to elevated
nutrient concentrations in ground and surface waters.