Vegetable BMP Research - 2006-2007 Season: Introduction
Seventy percent of the Florida tomatoes production is grown in South Florida counties
of Collier, Manatee and Palm Beach with approximately 41,200 acres in 2006 (NASS,
2006). Tomatoes are grown primarily in sandy soils. These crops are mostly grown
in South Florida in the fall, winter or spring growing seasons under intensive irrigation
and fertilizer management. Nitrogen (N) fertilizer management has become an issue
of environmental concern for Florida vegetable growers following the
adoption by the State of Florida of vegetable BMPs (Best Management Practices).
BMPs emphasize the need to better manage fertilizer, increase fertilizer efficiency,
and reduce N loss to the environment. The optimum fertilization management and application
section of the manual incorporates University of Florida (UF/IFAS) N rate recommendations.
The most common method for producing tomato in South Florida is to use seepage-irrigation
together with fumigated raised beds with polyethylene mulch. Therefore, nutrient
management is tied to this unique irrigation system. Because the plastic mulch covers
the soil surface, all fertilizers (N, P, K, and micronutrients) are applied pre-plant.
Typically, fertilizer is applied as a “bottom mix” (or “cold mix”) and a “top mix”
(or “hot mix”). All the P and micronutrients, and 20% to 30% of the N and K are
applied broadcast and incorporated in the bed as the bottom mix. The remaining N
and K are applied in 1 or 2 grooves made on the top of the bed. Fertilizer in the
“top mix” is slowly solubilized as the water moves up by capillarity (Olson et al.,
2006a and b). While this system is simple and well established, growers often use
N fertilizer rates above the UF/IFAS recommended rate because N may be lost by leaching
or denitrification (Cockx and Simonne, 2003), but mostly as an inexpensive insurance
if the market conditions remain favorable resulting in a longer-than-expected harvest
season. When soluble fertilizers are leached by excessive rainfall (a leaching rainfall
is defined as 3 inches of rain in 3 days or 4 inches in 7 days), UF-IFAS recommendations
(Olson et al., 2006a and b) and vegetable BMPs (BMP 33I, p.96 of the BMP manual
for vegetable and agronomic crops) allow for a supplemental application (per planted
acre basis) of 30 lbs of N and 20 lbs of K2O. Supplemental fertilizer applications
should be made after a leaching rain, not before, preventively. While drip irrigation
allows for easy in-season fertilizer application, crops grown with plastic mulch
and seepage irrigation require a down-the-row application of fertilizer, done either
manually or using a fertilizer wheel increasing the production cost.
BMP education is a slow process that requires the reconciliation of the rigor of
science with the reality of vegetable production today (Simonne and Ozores-Hampton,
2006; Cantliffe et al., 2006). However, when BMP education is based on trust and
a mutual commitment in the success of the project, a win-win situation develops
where productivity, profitability, and environmental impact are integrated. Since,
the first 3 x 100-ft long bed demonstrations conducted in the 2003-2004 season by
G. McAvoy and E. Simonne, a lot of trust has been developed between UF-IFAS, DACS,
and South Florida growers on nutrient management issues. This is best shown by the
number and size of trials conducted in 2006-2007 (multiple rate trials, randomization
and replication of the treatments, and 3-acre plots; Ozores-Hampton et al., 2006).