Horticultural Sciences Department

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Issue No. 614

The Vegetarian Newsletter 

A Horticultural Sciences Department Extension Publication on 
Vegetable and Fruit Crops 

Eat your Veggies and Fruits!!!!!

Publish Date: 
July 2016

Impacts of BMP Adoption by Suwannee Valley Watermelon Growers

Kevin R. Athearn and Robert C. Hochmuth

UF/IFAS Regional Specialized Extension Agents

Suwannee Valley Agricultural Extension Center

Nearly one-third of all Florida watermelons are grown in the Suwannee Valley. UF/IFAS specialists and county Extension agents have been working with the region’s watermelon growers for years to help them adopt plastic mulch and drip irrigation and to refine their water and nutrient management programs. This spring, with support from a FDACS-funded BMP mini-grant, we interviewed watermelon growers and reviewed prior studies to document these changes and estimated the resulting water, fuel, and fertilizer savings. The target population for the interviews was all 40 (approximately) watermelon growers in the Suwannee Valley region. We completed semi‑structured interviews with nine (23%) of the growers.

Over the past 25-30 years, watermelon growers in the Suwannee Valley started growing seedless watermelon varieties, started using transplants instead of direct seeding, changed from bare ground to plastic mulch, switched from overhead to drip irrigation, and adjusted their fertilization practices. Many growers have started using plant nutrient testing and soil moisture sensing tools to help them fine tune fertilizer applications and irrigation schedules. Grower interviews documented the timing and extent of those changes and provided insight on their motivations.

The transition to seedless watermelons took place during the 1990s and was driven primarily by market demand for those varieties. Some growers continued to grow seeded watermelons (in addition to seedless) to serve as pollinizers for the seedless crop or to sell to local and national markets. The transition from direct seeding to transplants coincided with the adoption of seedless varieties. Higher seed costs and lower germination rates in the field were factors contributing to the shift to transplants. The increase in seed costs was also partly driven by the seed industry’s management programs to reduce bacterial fruit blotch incidence.  Also, using transplants instead of direct seeding is one factor that enables an earlier harvest. Selling during an early market window gives growers greater access to national markets and allows them to obtain a higher price.

All interviewed growers reported transitioning to plastic mulch during the 1990s. Most growers started experimenting with plastic on at least some of their fields in the early 1990s. All interviewed growers had fully transitioned to plastic by 2000. Instead of planting watermelons in bare soil as had been done previously, growers now plant watermelons in mounded and  pressed rows including drip irrigation covered by black plastic mulch. The black plastic blocks weeds, reducing the need for herbicide except between rows, and warms the soil, allowing earlier planting and therefore earlier harvest. Plastic mulch culture also reduces the likelihood of leaching from rain events.

Prior to 1990, most watermelon growers planted in wide row spacing of 10-12 feet between rows and used overhead irrigation systems, primarily traveling volume guns. During the 1990s growers began to change irrigation systems. Initially, some growers continued using traveling guns while experimenting with photo-degradable plastic mulch, and a few switched from traveling guns to pivot irrigation. Ultimately, however, the industry rapidly transitioned to drip irrigation systems. All interviewed growers reported using drip irrigation for their watermelon fields by the early 2000s. As plastic mulch and drip irrigation were adopted, growers tended to reduce row spacing down to eight feet typically and increased plant populations in the row. Drip irrigation can save water, reduce labor and pumping costs, and reduce foliar disease problems, relative to overhead irrigation.

Along with the transition to drip irrigation and plastic mulch, fertilization practices changed. Growers started using less pre-plant dry fertilizer and started applying more through the drip system. Most interviewed growers described how they can more precisely deliver what the plant needs when it is needed using various tests and applying fertilizer through the drip system. Soil testing, leaf tissue testing, and petiole sap testing are practices that growers have been using to improve nutrient management and fertilizer efficiency. Interviewed growers started using leaf tissue testing or petiole sap testing or both in the last three to eight years. Only a few are using GPS to vary fertilizer rates within a field.

The interviewed growers were asked how they learned about different production systems and management techniques. All but one said they had learned from UF/IFAS Extension, including Extension agent field visits and IFAS classes or workshops. Growers mentioned other sources of information too, including other growers, crop consultants, the Florida Watermelon Association, Clemson University, and North Carolina State University.

We asked growers to estimate the amount of water, fuel, and nitrogen fertilizer they save using current practices relative to the practices used 25-30 years ago. Growers report reductions in water use per acre ranged from 50% to 80%, with most growers reporting water savings of 67% or more. Growers report that diesel fuel consumption for irrigation pumping has been reduced at least proportional to the reduction in water use. Some growers and engineering studies suggest that fuel savings are likely greater than proportional to the water savings. Although some growers believe they are using about the same amount of nitrogen per acre, most report reductions in applied nitrogen ranging from 15-30%. These estimates are likely very conservative because row spacing has decreased and plant populations increased.

All interviewed growers stated that their yields per acre have increased over the past 25 years. In the early 1990s, typical yields ranged from 25,000 to 40,000 pounds per acre. Although there was considerable variation in the current yield expectations among the growers interviewed, most growers reported typical yields of 50,000 to 60,000 pounds per acre in recent years.

Watermelon yields per acre have increased dramatically over the time period with less water and fertilizer inputs.

Relying on information from the grower interviews and parameters on water, fuel, and fertilizer rates from other studies, we provide ballpark estimates for the total savings on 6,000 acres of watermelon fields in the Suwannee Valley over the past 25 years. Irrigation changes made by watermelon growers have saved approximately 2 billion gallons of water per year. Fuel and fertilizer savings are more difficult to estimate with confidence, but fuel savings of at least 120,000 gallons per year and nitrogen savings of about 180,000 pounds per year appear realistic.  

Suwannee Valley watermelon growers have reduced water, fuel and fertilizer use, and improved efficiency. More watermelons are being produced with less water and in most cases less nitrogen fertilizer per acre. Improved nitrogen efficiency implies that a greater percentage of applied nitrogen is being taken up by the plant and less nitrogen is being lost to leaching. Similarly, more efficient irrigation through a drip system and soil moisture monitoring implies less leaching. Taken together, these changes indicate a substantial reduction in the likelihood of negative impacts from watermelon production on the region’s water quality.



Headlines like this one are the saddest thing in the world for people in the UF/IFAS Farm Labor Supervisor Training program because we teach Rules & Regulations for Labor Bus and Van Drivers and Safe Driving.   

According to reports, a labor bus traveling from Bainbridge, Georgia was heading to Belle Glade for a few weeks of rest before heading north to pick apples and berries.   The bus passengers were 35 Haitian migrant workers and their families.   The bus blew through a blinking red light (and stop sign) and hit a semi-truck that disintegrated on impact.  The driver of the 1979 Blue Bird Bus, 56, was in critical conditions.  The driver of the semi died from his injuries but his passenger was not hurt.  Five migrant workers were killed, including one child.  The bus hit the truck and then slammed into a power pole at about 5:00 a.m., and both vehicles burst into flames.  Skid marks indicated the truck had hit his brakes only seconds before the impact.    The investigation is ongoing, but we will begin our transportation classes this season with this story and this question: 

What could have caused the crash?   We will ask the class to call out possible answers, before going over all the rules and regulations that might have saved these people.  Thinking through just the facts presented above, here are a few possibilities, all having to do with the driver and the vehicle:

1.       The driver was sleepy and didn’t notice the flashing red light.  Did he get enough sleep?  Would his log book have shown that he didn’t have enough rest in between driving shifts?  Did he keep a log book at all?

2.       The driver’s physical condition – did he have eyesight issues?  Did he have a DOT-required medical card, which would mean he at least had had his vision checked?

3.       Did he have a cold and did he take over-the-counter medications that  made him dizzy or tired?

4.       Weather?  Was it foggy, or rainy, impairing his vision? 

5.       The vehicle – 1979 is an old bus and may have had worn brakes.  Was it properly inspected, annually by a qualified mechanic and that morning and the previous evening by the driver? 

6.       Was the driver distracted by a cellphone or by someone in the bus talking to him as the bus approached that light?

We will think through more possibilities this fall and at private trainings throughout the year from our classes.   In the meantime, hopefully law enforcement will come up with the real truth, but with a fire-gutted frame that was all that was left of the bus, the answers may never come. 

Farm Labor Supervisor training will be held at several locations this fall, to be announced soon.  Private trainings are available any time, in any location. 

For more information, contact Carlene Thissen carlene@ufl.edu , 239-658-3449 or Fritz Roka, fmroka@ufl.edu  .   

Fertigation for Potato Production in Florida


1Xiangju Fu, 1Guodong Liu, 1Lincoln Zotarelli, 1Steven Sargent, 2Crystal Snodgrass, and 3Alan Jones

1Horticultural Sciences Department, University of Florida-IFAS, Gainesville, Florida, USA, 32611

2Manatee County Extension, University of Florida-IFAS, Palmetto, Florida, USA, 34221

3Jones Potato Farm, Parrish, Florida, USA, 34219

Potato is a major vegetable crop grown on approximately 32,000 acres in Florida. Seepage is the basic irrigation method in the state. Our previous study shows that conversion from seepage to center pivot irrigation saves more than 50% of irrigation water in southwest Florida (Liao et al. 2016, http://hos.ufl.edu/sites/default/files/faculty/gdliu/Liao2016.pdf). This conversion is promising to alleviate Florida’s potential water shortage. Center pivot irrigates potato plants from the top.The nutrients, particularly, nitrogen is easily washed away from the root zone. Seepage irrigates the crop from the bottom and the nutrients can stay in the root zone much longer than center pivot irrigation. Irrigation and fertilization go hand in hand. When the irrigation method changes, the fertilization method needs to follow the change as well. Fertigation is defined as the injection of fertilizers into an irrigation system.In this study, fertigation was used with center-pivot irrigation for potato production.

Applying nutrients in nutrient solution, namely, liquid fertilizer, that can be readily absorbed by crops as compared with granular fertilizers incorporated into soil; and hence, the nutrient use efficiency can be significantly improved. Currently, fertigation is used through drip irrigation systems for commercial production of cash crops; mainly, tomato and strawberry. (Kennedy et al, 2013; Choi et al, 2011; Mahajan et al, 2006; Ajdary et al, 2007; Bhat et al, 2009; Farneselli et al, 2015). Studies show fertigation increases crop yields and enhances nutrient use efficiency. However, fertigation used for potato production is new to Florida producers.

The objectives of this study were to: (1) explore the feasibility of fertigation through center-pivot irrigation for potato production; and (2) evaluate water usage between the two treatments including irrigation water applied solely through center pivot, and irrigation water applied partially through both center pivot and partially through seepage.

Materials and Methods

The trial was conducted at a commercial potato farm in Manatee County, FL. Potato ‘Atlantic’ was planted on 12/25/2015 and harvested on 4/4/2016. Two irrigation treatments: fertigation and dry granularwere established and replicated four times under two side-by-side center pivots. The fertility rate was the same in both treatments, but the source of material varied. Fertilizer was applied three times at the following crop stages and rates: dry granular: pre-plant application (80, 120, and 150 lb/a N, P2O5 and K2O; respectively), at crop emergence (100, 0, 100 lb/a N, P2O5 and K2O; respectively), and at layby, five weeks before harvesting (50, 0, and 50 N, P2O5 and K2O; respectively. All fertilizers were dry granular. The only difference in the fertilizer program for fertigation was that no dry fertilizers were applied at layby, instead, 5 fertigation events were performed with an interval of a week starting at tuber initiation stage. Every fertigation operated at an N rate of 10 lb N/acre with approximately 0.2 inches of irrigation water (see Table 1). Tubers were dug from the central 20 ft in the two middle rows of each plot. The tubers were graded at UF/IFAS Hastings Agricultural Extension Center, Hastings, Florida after harvest. Four rain gauges were installed beyond the irrigation range of the center pivots in the experimental area to record the rainfall in the growing season. Irrigation water usage was recorded by mechanic flow meters. Another 4 rain gauges were installed to record the water applied through pivots. The irrigation water rate from center pivot irrigation was calculated by comparing the average values from both of the rain gauge readings under and outside the pivot. Water application through seepage was calculated by subtracting pivot water usage from the total water usage. Yield and water savings were calculated by contrasting those between fertigation and dry granular fertilizer only.

Table 1. The fertilizer program for the two treatments in this study


*50 lb/A each of N and K2O were equally fertigated starting 4 weeks after emergence through the center pivot with a one-week interval for five times

Result and Discussion

The yield data (Figures 1 and 2) showed that the average total yield of fertigation was 16% greater than dry granular fertilization, and the marketable yield of fertigation was 19% greater than that of dry granular fertilization. Most of the tubers measured between 1.88 to 2.5 inches in diameter for both of the treatments: fertigation and dry granular fertilization.

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Photo 1. Potato grown with fertigation. The vines were uniform. The dry fertilizers were applied two times: pre-plant application (80, 120, and 150 lb/A N, P2O5, and K2O; respectively), at crop emergence (100, 0, 100 lb/a N, P2O5 and K2O; respectively), then 50 lb/A each of N and K2O were equally fertigated starting 4 weeks after emergence through the center pivot with a one-week interval for five times.

image006_0.pngPhoto 2. Potato grown with dry granular fertilization and the vine growth varied dramatically. The dry fertilizers were applied three times: pre-plant application (80, 120, and 150 lb/a N, P2O5, and K2O; respectively), at crop emergence (100, 0, 100 lb/a N, P2O5 and K2O; respectively), and at layby, i.e., five weeks before harvesting (50, 0, and 50 N, P2O5 and K2O; respectively).


Photo 3. Fertigation for potato system showing that the liquid fertilizer in the

300 gallon tanks was injected into the center pivot by the injector (three phase-55 gallon per hour). Each injection took approximately 7 hours to complete.


Figure 1. Total potato tuber yields for both fertigation and dry granular fertilization. The fertigation treatment had 16% greater yield than the dry granular fertilization treatment.


Figure 2. Potato tuber yield by size. The fertigation treatment had 14% less small tubers but 23% to 26% more medium, large and extra-large tubers than dry granular fertilization.

Table 2. The difference in mean values of tuber yield by size between the fertigation and dry granular fertilization in spring 2016


Tuber yield

Tuber size (inches)

Marketable yield

Total Yield
















Dry granular

















Dry granular








Figure 3 summarizes total water application by treatment for the growing season. Rainfall contributed more than half of total water usage for the growing season. For the dry granular fertilization, a hybrid irrigation system was adopted and most of the water was applied through seepage. The irrigation for fertigation treatment was solely overhead irrigation. The irrigation water used in the fertigation treatment was only 27% of that used in dry granular fertilization. The reason for this difference was that seepage irrigation had to be used for dry granular fertilization to keep the applied nutrients staying in the root zone longer. Otherwise, the nutrients from the applied dry fertilizers were washed out from the root zone.


Figure 3. Total water usage of either fertigation or dry granular fertilization. Fertigation saved 73% of irrigation in this growing season.

Summing up, spring 2016 was a wet growing season in southwest Florida. Irrigation water usage was only 2.11 and 7.90 inches in the Fertigation and Dry granular treatments; respectively, while rainfall contributed 10.63 inches. Thus, compared to the hybrid irrigation system, the sole center pivot irrigation used 73% irrigation water in this growing season. The Fertigation treatment productivity was greater in total (16%) and marketable tuber yields (19%) than dry granular fertilization. This was the first trial evaluating fertigation as an alternative irrigation and fertilization method to standard grower practice of center pivot irrigation and soil incorporated dry granular fertilizer, and more trials are needed.


This study is supported by Southwest Florida Water Management District (SWFWMD) (Contract #: 00098762). We thank Mr. David Fleming at Jones Potato Farm and the crew of Hastings Agricultural Extension Center for helping with this research.