Horticultural Sciences Department

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Issue No. 575

The Vegetarian Newsletter 

A Horticultural Sciences Department Extension Publication on 
Vegetable and Fruit Crops 

Eat your Veggies and Fruits!!!!!

Publish Date: 
July 2012

Optimizing Phosphorus Rate is Imperative for Improving the Sustainability of Commercial Snap Bean Production in South Florida

1Guodong Liu, 2David Sui, and 3Yuncong Li

1Horticultural Sciences Department, University of Florida, 1117 Fifield Hall, Gainesville, FL 32611-0690,

2Palm Beach County Cooperative Extension, University of Florida, 559 N. Military Trail, West Palm Beach, FL 33415-1311

3Tropical Research and Education Center, Soil and Water Science Department, University of Florida, Homestead, FL 33031

Florida is ranked first in the production, acreage, and total value of fresh market snap bean in the nation (http://www.florida-agriculture.com/consumers/fnr/healthyeating/fresh2u/snapbean.html). South Florida is the principal region for snap bean production. Fertilization is essential for snap bean production. Of the major nutrients, phosphorus (P) is a vital component of adenosine tri-phosphate (ATP) which stores and supplies the energy for the biochemical and physiological processes in the crop plant. Phosphorus is fundamental to the successful development of snap bean and other crops. However, we have to face three key challenges in fertilization for commercial crop production:

1.Economic challenge: based on the data from the USDA National Agricultural Statistics Service, fertilizer prices have escalated since 2000 and increased approximately 10-fold last decade (Figure 1) due to energy prices rise. Thus, snap bean growers have to operate at very thin profit margins. To sustain their profitability, efficient-use of phosphorus is imperative.

2.Mineral resource challenge: all of P fertilizers are produced from nonrenewable mineral P rock. Florida is a leader in P-fertilizer industry and provides 75% P fertilizers for the nation and 25% for the whole world. However, according to the data from USGS, the phosphate rock in Florida will be depleted in approximately another two decades. In fact, the P fertilizer industry has started importing P rock from Morocco or other countries (Cordell et al., 2009). A potential phosphate crisis exists and will occur (Abelson, 1999). Because only a few countries are relative rich in P-rock resources, a new OPEC-an Organization of Phosphate Exporting Countries may arise in the near future (Epstein and Bloom, 2005). This depletion of P mineral resources requires us to use P fertilizers wisely and effectively.

3. Ecological challenge: P fertilizers have three fates after being applied to the soil: plant uptake, soil fixing, and leaching which causes water pollution, i.e., eutrophication. Snap bean plants remove only 36 pounds of phosphorus pentoxide at bean yield of 10,000 pounds/acre (Maynard and Hochmuth, 1997). In Florida, the yield is much lower than 10,000 pounds per acre. This indicates that the actual amount of phosphorus pentoxide removed by snap bean is much less than 36 pounds. The leftover phosphorus can create or contribute to eutrophication. South Florida is where the Everglades are located. Because the Everglades are extremely oligotrophic, the U.S. Environmental Protection Agency (USEPA) has determined that an annual or longer term mean of 10 μg P L-1 (parts per billion, or ppb) would protect the Everglades flora and fauna (Payne et al., 2003). However, the P concentration of ground water in the Everglades had recorded high up to 1,136 ppb in the wet season. As a nonpoint source, crop production contributes to the P content in the water. To protect the environment and ensure long-term food safety and security, optimizing P management is crucial for the sustainability, productivity, and profitability of snap bean production.

Figure 1. Changes in fertilizer prices from 1960 to 2009.

To ensure P-use efficiency and enhance economic and ecological sustainability, the UF/IFAS recommendation of P rate for snap bean is in a range from 80 to 120 lb/acP2O5 based on the P bioavailability in the soil. However, current practice uses as much as 200 lb P2O5 per acre in commercial vegetable farms in south Florida such as in Palm Beach County. The objective of this study was to demonstrate the optimum P rate for improving the productivity of snap bean production.

This study was in a randomized complete block design with four replications using a commercial cultivar (Caprice) and seven P rates: 0, 40, 80, 120, 160, 200, and 240 lb P2O5 per acre in Hundley Farms Lake Harbor in Palm Beach County from November 21, 2011 to February 1, 2012. Soil was muck soil with pH 6.0±0.1. The plot size was 600 square feet with 8 rows in length of 30 feet. The row space was 2.5 feet and in-row space 2 inches. The number of seeds sowed was 104,544/acre. The central 20 feet of the central 2 rows were harvested. The harvest area was 100 square feet. Marketable beans were harvested. This trial was repeated with the same settings in sandy soil in Hundley Farms in Belle Glade in Palm Beach County from March 1 to April 27, 2012.

Figure 2 indicated that application of phosphorus increases marketable bean yield significantly at low P rates. But yield increment became smaller or even negative with P rate increase. In the first trial, bean yield reached the maximum yield at 120 lb P2O5/acre and then slightly reduced with P increase. Similarly, in the second trial, bean yield increased significantly from 0 to 120 lb P2O5/acre but any further increase of P did not increase marketable yield significantly even though the treatment with 240 lb P2O5/acre had the maximum marketable bean yield. Based on the 2-year trial data at two sites, the bean yields showed that 120 lb P2O5/acre was the optimum P rate for snap bean Additional P application resulted in insignificant increase or decrease of marketable bean yield.

Figure 2. Snap bean marketable yields at different P rates in trial 1 from November 21 2011 to February 1, 2012 and trial 2 from March 1 to April 27, 2012. The yields of the both trials followed a saturation law. P rate of 120 lb phosphorus pentoxide was the best.

Figure 3. Changes in the ratio of bean length to bean diameter (L/D value of beans) at different phosphorus application rates in the second trial from March 1 to April 27, 2012.

The ratio of bean length to bean diameter is an important parameter of bean quality. Since bean diameters did not increase much but bean length did at P rate of 120 lb P2O5/acre or lower and the opposite for both bean length and diameter was true at P rate of 160 P2O5/acre or higher, the maximum L/D value lies in the P rate of 120 P2O5/acre.

In summary, P application can significantly increase marketable bean yields at P rate of 120 lb P2O5/acre or lower but the bean yield obeys a saturation law and did not increase significantly at any higher P rates. Bean quality analysis also showed that the treatment with 120 lb P2O5/acre had the maximum L/D value. Therefore, these trials indicated that P application of greater than 120 lb P2O5/acre may reduce the profitability and sustainability of snap bean production in south Florida. The UF/IFAS recommendation for P application rates, ranging from 80 to 120 lb P2O5/acre, was validated in these trials.


Abelson, P.H. 1999. A Potential Phosphate Crisis. Science. 283(5410): 2015.

Dana Cordell, Jan-Olof Drangert, Stuart White. 2009. The story of phosphorus: Global food security and food for thought . Global Environmental Change. 19: 292-305.

Epstein, E. and A.J. Bloom. 2005. Mineral Nutrition of plants: Principles and Perspectives (2nd edition).  Sinauer Associates, Inc. Sunderland, MA.

Maynard, D.N. and G.J. Hockmuth. 1997. Knott’s Handbook for Vegetable Growers (4th edition). John Wiley & Sons, Inc., New York.

Payne, G., T. Bennett, and K. Weaver. 2003. Development of a numeric phosphorus criterion for the Everglades Protection Area. Chapter 5. In 2003 Everglades Consolidated Rep. South Florida Water Management District, West Palm Beach.

National Association of County Agricultural Agents (NACAA)

2012 National Winner: Search for Excellence, Category Farm Health and Safety

Recognition at NACAA Annual Meeting, Charleston South Carolina, July 15-19

“Teaching Farmers to Build their Own Food Safety Manual”

By Robert Hochmuth, Linda Landrum, Elena Toro, and Dan Fenneman, University of Florida IFAS, County Extension Agents

A team of Florida County Extension Agents recently received the 2012 Search for Excellence Award from the National Association of County Agricultural Agents in the area of Farm Health and Safety. This national award was based on the team’s work for helping farmers develop and implement food safety plans. The team of Extension agents recognized in 2012 included Robert Hochmuth, Linda Landrum, Elena Toro and Dan Fenneman. This same award’s national winners in 2011 were also County Agents from Florida Extension, Alicia Whidden and Crystal Snodgrass. The recent increase in food safety requirements on farms has put added financial, time and personnel burdens on farmers. As increasing pressure from produce buyers on farmers emerged, small and mid-sized farmers in Florida were becoming very aware of the need to develop farm food safety plans. Most small farms do not have the financial capacity to hire personnel to develop and implement these plans and asked for help from Extension Agents. A total of 14 workshops to 185 producers and packers were offered in the last 2 years. Agents taught farmers how to develop their own food safety plan and implement practices on their farm. The Extension Agents were able to further develop the program by securing funding support through a Specialty Crops Block Grant from Florida Department of Agriculture and Consumer Services.  Farmers valued the training and indicated they viewed food safety plans as very important and plan to implement a food safety program on their farm.  The first two years of the trainings provided by Extension Agents have saved farmers an estimated half million dollars in fees that would have been paid to someone outside the farm to prepare their farms for the food safety audits required by the produce buyers. The success of this program has recently expanded and 25 County Agents are now trained and offering workshops in at least a dozen locations in the state.

The County Agent team recognized the instrumental support from key Extension specialists Dr. Keith Schneider, Dr. Danielle Treadwell and Dr. Sebastian Galindo. The 2012 award entry details are provided below.


Fresh produce growers, large or small, are aware that meeting food safety requirements has become one of their dominant challenges. Smaller farms do not have the financial capacity to pay additional personnel nor hire a consultant to help with the process of developing a manual and preparing for a third party food safety audit.  This program was initially developed and implemented by county agents in the Suwannee Valley to help a very diverse group of fruit and vegetable growers to develop a manual and prepare for a third party food safety audit. The success of this program occurred at a time when county agents from other areas of the state identified the same needs, but felt unprepared to offer such training.

Educational Objectives

I. Develop a training program for small and mid-sized farmers to develop food safety plans and manual.

II. Implement an in-service training program for Extension agents and develop a statewide Extension Small Farms Food Safety Implementation Team.

Program Activities        

  • Strategize a plan for program development. A series of funding opportunities were secured through the Florida Specialty Crops Block Grant program and the University of Florida, Office of Sustainability.  Over the three year period (2009-2011), total grant funding secured for this overall effort was $77,000 which included the purchase of ten laptop computers.
  • Curriculum.  Agents developed a written curriculum guide for farmers to follow when using a web-based tool. A notebook was compiled that included agent developed materials such as PowerPoint presentations, audit supporting documents and a pictorial self-audit exercise. Farmers received a food safety tool bag that contained worker training DVDs, hand washing signs and other resources to be used back on the farm.
  • Build Your Own Food Safety Manual Workshops. A total of 14 workshops were offered in Florida to 185 producers and packers. These workshops were offered using the Primus Labs web site, www.primuslabs.com.  The development of a complete farm food safety manual is not an easy process regardless of which tool is used, but the Primus Labs site seemed to be the most complete at the time with a relatively user- friendly menu driven system. The county agent team co-taught workshops with every farmer or farm family members at a computer logged into the site.  If a farmer requested to attend the training, but was not comfortable with the computer, an Extension staff person was provided as a “training buddy” for the training. The trainings included the exercise of working through a “self-audit” which helps provide the farmer insight into the guidelines followed by auditors.   

·            Extension Small Farms Food Safety Implementation Team.  A team of 19 Extension agents were trained in a formal two-day in-service training to learn how to use the Primus website, become familiar with all training materials developed for farmers, and establish a statewide team that could serve small farmers and help each other. These agents expanded the original five workshops of this program to a statewide presence and conducted a total of nine workshops. One of these workshops was featured at the Florida Small Farms and Alternative Enterprises Conference in Kissimmee, FL with 50 farmer participants.

  •  Food Safety Farmer Field Days.  As an advanced form of training, on-farm field days, were conducted as a follow up with farmers. One field day targeted watermelon growers, a second field day was offered to mixed-vegetable and protected agriculture growers. During the second field day, a third party auditor and extension agents re-created an actual successful farm field audit that had previously taken place at the farm of one of the workshop participants. 
  • Affiliated Activities. Due to recognition of this Extension program, agents involved were selected to host a delegation of food safety regulators from the Food and Drug Administration (FDA) and Florida Department of Agriculture and Consumer Services (FDACS) to visit local farms that were implementing food safety plans. In addition, these agents were selected to host one of three national listening sessions held in Florida being conducted by the Produce Safety Alliance to gain producer input for designing and delivering successful training and outreach programs in the area of food safety.

Teaching Methods

The primary method of teaching was face-to-face classroom instruction using the food safety web tool as a guide. Other methods included experiential learning via farm tours and follow-up farm visits to reinforce the concepts learned during the workshops and to help farmers to assess risks and to continue on-farm implementation of their plans.


·         A total of 14 workshops were offered in Florida to 185 producers and packers. The county locations of the nine trainings were: Suwannee (4), Escambia/Santa Rosa (4), Sumter (2), Alachua, Washington, Osceola and Polk.  All participants successfully built their food safety plan using the resources provided during the class. The educational material supplied to farmers was valued at $150 per farmer for a total value of $27,750.

·         A total of 19 Extension agents participated in the Agent In-Service training. As a result, 12 agents have offered trainings in their counties or region within the first year. This training helped agents gain the knowledge and confidence to deliver information in this emerging priority area.

·         Food safety updates have been offered to farmers during their annual meetings (i.e. watermelon growers meeting) to provide continuing education credits for those that need annual training as part of the on-farm food safety program.

By engaging in this effort, Extension agents have maintained a high level of relevance to their farm clientele in an ever changing regulatory environment.

Impact Statement

 Overall, the evaluations showed the farmers valued the training, viewed food safety plans as very important and plan to implement a food safety program on their farm, even though most were not being required to develop one by their buyers or markets. Nearly half of the farmers indicated they plan to have a third party audit, customer or regulatory audit conducted.  An estimated fee quoted by a private consultant for the cost of him developing a food safety manual and preparing the farm for an audit was $5,000 to $10,000.  Even at the lower figure, these trainings provided a savings of at least $460,000 in fees to those 92 farms that planned to be audited.  

The success and impact has been two-fold; more agents now have the expertise and skill to teach farm food safety reaching many more farmers and secondly, well over 150 farmers have developed plans. The program has garnered great respect and recognition statewide for Florida County Extension Agents from agricultural industry leaders.


Qualitative and quantitative data collection methods were used to document the impact of this initiative. A variety of assessments that included surveys, pre and post tests, follow-up phone calls and farm visits to assess implementation of practices have been conducted during the past three years. The primary method used was an on-line evaluation that was completed after each workshop. The results of the evaluation led to improvements in the workshops, including: addition of a pictorial review of real farm food safety issues, improved methods in reviewing the self-audit module, and the implementation of advanced trainings on farms.

An Experiential Learning Approach to Teaching Vegetable Gardening

Linda Seals, Elizabeth Shephard, Sally Scalera, UF/IFAS Brevard County Extension

Jim Fletcher, UF/IFAS Osceola County Extension

In 2010, the Brevard County Extension office recognized a significant increase in requests for information on growing, preserving, and cooking fresh vegetables. While providing information in the form of EDIS publications or short classroom lectures can increase knowledge, seldom does this give learners the confidence to start gardening and/or preserving on their own. To build confidence in learners, the agents took a collaborative, hands-on approach and created the "Be Healthy, Grow Your Own: Vegetable Gardening in Florida" program.

The agents involved in the development and implementation of the program included urban and commercial horticulture, agriculture, and Family and Consumer Sciences. The program consisted of 12 weeks of 2-hour classroom lecture followed by 2-4 hours of hands-on instruction in the garden. Master Gardeners and agents circulated throughout the garden after the lectures to provide recommendations and advice to participants (Fig. 2).  Everything grown by the participants was theirs to keep. Participants were encouraged to grow vegetables they had never tried to encourage them to eat more vegetables.

The garden, which is located on the Brevard County Extension campus, was divided into 45 20x20 foot plots (Fig. 3). Participants were assigned a plot where they could practice the skills and techniques learnt in the classroom. Course topics included plant selection, planning the garden, fertilization, irrigation, pest management, harvesting, cooking, and preserving, and more. All materials necessary for gardening were provided—seeds, transplants, which were grown by Master Gardeners in a grant-funded greenhouse built by the agent with some assistance, soil amendments, equipment , irrigation, and more. Participants also received a binder full of publications, books, loupe, and other educational materials.

To date, two classes have been delivered with nearly 80 participants in each class. A six-month, follow-up survey was delivered to participants in the first class (the second recently ended). Thirty-eight of the 40 participants (95%) who responded to the survey said they felt confident about vegetable gardening on their own after taking the class compared to only 11 who felt confident before taking the class. Thirty-eight respondents indicated they consumed fresh vegetables before taking the class; 40 participants indicated they consumed fresh vegetables after taking the class.  The agents concluded that the survey instrument needs to be changed to better collect data about consuming fresh vegetables. Also, people who are interested in vegetable gardening may already consume more fresh vegetables than other people, so maybe that objective needs to be reconsidered. More surveys will be conducted in the future to determine other impacts the program has had on producing and consuming fresh vegetables.

The enthusiasm from the class participants was overwhelming. From satisfaction with the class overall to confidence in gardening on their own, feedback from the participants was unanimously positive (Fig. 4). The following is a quote from one of the class participants:

“Just a note to let you know that I am still getting tomatoes and Brussels sprouts out of my plot #6!  Bigger news is that I have started my own garden on my property.  I will be planting this March on a 12’ by 8’ plot.  Wish me luck!”

More than 50 Master Gardeners volunteered over 2,100 hours to help implement the program. The various activities - everything from helping with classroom logistics to growing transplants - provided Master Gardeners with new activities as well as providing new learning opportunities that have increased their effectiveness when serving clientele. Several new small farmers participated in the lectures only. The possibility of including more small farmers will be explored for future programs.

The class participants became effective advocates for Extension. The cross-discipline programming made them aware of the variety of educational programs provided by Extension. The second class joined together to write and deliver letters of support to County Commissioners.  Participants donated tools and equipment, helped each other maintain plots, and volunteered to help Master Gardeners. In the end, a feeling of community was established while the program objectives were met.

The 2012-2013 class, which starts in September, is almost filled. Plans for the next class include a plot for a local faith-based youth group who wants to learn about vegetable gardening. This group will be led by one of the 4-H agents, and lectures will be held on a different day. The agent recently secured funding and purchased a tractor, which will help with preparing the grounds between classes.

Fig. 1. Data collected from a post-reflective survey conducted after the first class (n=40).

Fig. 2. A Master Gardener assists a class participant with tilling the soil.

Fig. 3. Participants were encouraged to be creative with their plots.

Fig. 4. A participant proudly displays her crop.