Horticultural Sciences Department

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Issue No. 603

The Vegetarian Newsletter 

A Horticultural Sciences Department Extension Publication on 
Vegetable and Fruit Crops 

Eat your Veggies and Fruits!!!!!

Publish Date: 
July 2015

Sustainable Phosphorus and Gypsum Management for Potato ‘Atlantic’ Production in Northeast Florida

Yuqi Cui, Guodong Liu, Lincoln Zotarelli, Steven Sargent, David Dinkins

Phosphorus and calcium are essential for potato production. The UF-IFAS’ new recommendation with Mehlich III extraction method is less than 25 to 40 parts per million (ppm) (115 to 184 lb/acre P2O5) for P application in vegetable production throughout the state. We surveyed for extractable P and Ca on 32 private farms from the Hastings area. The data shows that the extractable P ranged from 81 to 599 ppm (372 to 5,508 lb/acre P2O5) (Liao et al., 2015), which is 2 to 15 times greater than the IFAS recommendation. The IFAS recommendation for Ca is 300 ppm (840 lb/acre calcium oxide, CaO) (Liu et al., 2015). Extractable Ca was in a range of 374 to 3,362 ppm (1,047 to 4,707 lb/acre CaO). These extractable P and Ca seemed extremely high in the soils. However, tuber yield responses to P application to the soil with 170 ppm P (779 lb/acre P2O5) were observed during the recent years. Thus, the objectives of this study were to: (1) optimize P and Ca application rates for potato production and (2) increase awareness among the potato growers about improved nutrient management practices.

Materials and Methods

This trial was conducted at UF/IFAS Hastings Agricultural Extension Center, Hastings, Florida from February 16 to May 28, 2015. There were 12 treatments including six levels of P (0, 40, 80, 120, 160, 200 lb/A of P2O5) and two levels of Ca (0, 500 lb/A of gypsum containing 23.3% Ca), arranged in a randomized complete block design and replicated four times for a total of 48 plots (6×2×4).  Plot size was 533.3 ft2 (four 40 ft long rows). Row spacing was 40 in and plant spacing was 8 inches. At harvest, tubers were dug from the central 20 ft each in the two middle rows in each plot. Tubers were weighed, and assigned to one of five diameter groups in inches (<1.88, 1.88-2.5, 2.5-3.25 and 3.25-4 and >4). Twenty potato tubers randomly collected from either of the two harvested rows in each plot were assessed for specific gravity and the following internal quality characteristics: hollow heart (HH), brown rot (BR), corky ringspot (CRS), internal heat necrosis (IHN) and brown center (low, medium, or high degree of browning).

Statistical Analysis

Data were analyzed using the two-way ANOVA method, and differences were considered significant at p < 0.05. After running the SAS program (SAS Institute, 2012), the critical ranges (LSD2, 0.05) of Duncan’s Multiple Range Test were used to detect the difference significance between the means of the total tuber yields of different P or gypsum rates.

Results and Discussion

Figure 1 shows the total tuber yields with different P rates. Significant differences (P<0.05) of the total potato yields were observed between the zero P application and each of those with the P application rate of greater than 80 lb/A. Gypsum did not influence yield in this trial (Figure 2). These results may be attributed to high pre-trial concentrations of phosphorus and calcium as a result of decades of applications of triple superphosphate or super phosphate in the potato production in the area. To enhance P and Ca use efficiency and minimize the environmental risk of eutrophication, P application should be controlled with not more than 80 lb/A.



Gypsum application may not be needed for commercial potato production in the area, but more trials are needed. Similarly, external and internal qualities of the potato tubers were similar among the six P fertilizer rates and two gypsum rates in this study. Tuber specific gravity is very important to chipping potatoes. The results of this trial also showed that there was little difference in specific gravity among the P and gypsum application rates (Table 1).

Summing up, the data from this trial indicated that the application of P did not significantly contribute to increasing in tuber yield when the P rate was greater than 80 lb/A in the growing season (Figure 1 and Table 1). Gypsum application rates were not significantly different at all (Figure 2 and Table 1).  This result suggests P applications of greater than 80 lb/A are not likely to result in an increase in yield and therefore are not recommended. Gypsum may not be needed for potato production in this area. To verify our observations of the effects of P and Ca application rates on potato yield and tuber quality, this trial will be repeated with the same experimental design during the next growing season.



This study is financially supported by the USDA-AMS through Florida Specialty Crop Block Grant Program (Contract #: 00096316, Project #: 00120641). We thank Director Scott Taylor and his staff for helping us with field management and harvest.


Hubbard, M.R. 2001. Statistical Quality Control for the Food Industry (2nd edition). Aspen Publishers, Inc., Gaithersburg, MD, USA.

Liao, X., G.D. Liu, B. Hogue, and Y.C. Li. 2015. Phosphorus Availability and Environmental Risk in Potato Fields in North Florida. Soil Use and Management 31(2): 308-312. Accessed July 10, 2015. http://hos.ufl.edu/sites/default/files/faculty/gdliu/PublishedSum12186.pdf

Liu, G.D., Y.C. Li, and A. Gazula. 2014. Conversions of parts per million on soil test reports to pounds per acre. HS 1229. Gainesville: UF/IFAS. Accessed July 10, 2015. https://edis.ifas.ufl.edu/hs1229

Liu, G. D., E. H. Simonne, K. T. Morgan, G. J. Hochmuth, M. Ozores-Hampton, and S. Agehara. 2015. Fertilizer Management for Vegetable Production in Florida. CV296. Gainesville: UF/IFAS. Accessed July 10, 2015. http://edis.ifas.ufl.edu/pdffiles/cv/cv29600.pdf

Sweet Potato Production and Wireworm Pests in North Florida

Robert Hochmuth1 and Daniel Fenneman2

1UF/IFAS Regional Specialized Extension Agent, Commercial Vegetable Crops,

Suwannee Valley Agricultural Extension Center

2 UF/IFAS Madison County Extension Agent, Agriculture and Natural Resources,

 Madison County Extension

Acreage of sweet potato in North Florida was traditionally limited to small acreages on several smaller farms, mostly for local sales. The Florida sweet potato acreage reported in 2011 was 480 acres and in 2012 was 756 acres (http://freshfromflorida.s3.amazonaws.com/P-01304.pdf). Recently the sweet potato industry in the Suwannee Valley of Florida and the very southern edge of Georgia has changed dramatically. There are still smaller growers with 5 acres or less for local sales, but now there are also a few much larger operations growing and selling to wholesale chains and processors. As a result, the current best estimate of sweet potato production area in 2014 was at least 2000 acres in North Florida and increases again in the region put acreage estimates for 2015 over 3,000 acres.

One of the most serious pests of sweet potato in the region is wireworm as it damages the sweet potato roots to be harvested. The feeding damage appears as small holes drilled into the potato, usually the holes are not very deep. The larva (worm) is the stage that feeds on the sweet potato in the ground, and yet the adult stage is the familiar click beetle often found at night attracted to outdoor lights. The feeding of the larvae reduces the grade and market value of the sweet potato, generally forcing the damaged sweet potatoes to be used for lower value processing markets rather than premium fresh market grades.  Future increases in North Florida sweet potato acreage will depend on a successful Integrated Pest Management (IPM) program targeted at wireworm larvae.

An intensive integrated pest management survey was conducted on four farms in Suwannee and Madison County in 2014 by county and regional Extension Agents. This pest survey project included several UF/IFAS faculty including Extension specialists, Dr. Dak Seal, Dr. Susan Webb, Dr. Russ Mizell, and Dr. Norm Leppla; and County Extension Agents, Robert Hochmuth, Dan Fenneman, Elena Toro, staff from the Suwannee Valley Ag Extension Center, and program assistant Andrew Horvath.

The team of UF/IFAS state and county faculty was developed to assist local growers by implementing a season-long scouting program. Four fields (one in Madison and three in Suwannee County) were instrumented with yellow sticky traps, grain bait stations in the soil, and black light traps to detect and characterize the populations. Assessments of damage were made in each field at harvest. In addition to surveying for wireworm, pheromone traps were placed in the fields to detect sweet potato weevil. No adult weevils were detected all season long and no damage by the weevil was noted in any of the fields surveyed.

The 2013 project identified the two main wireworm species affecting the acreage in North Florida. The two species identified, Conoderus rudis (http://edis.ifas.ufl.edu/pdffiles/in/in90900.pdf) and Conoderus scissus (http://edis.ifas.ufl.edu/in911), are not the same primary species as those found in other production areas of South Carolina, Alabama, Mississippi, and North Carolina. Damage in fields can be very severe with wireworm-damaged sweet potatoes well over one-third of all harvested potatoes. Successful IPM programs will need further development to result in the following targeted impacts: reduced overall insecticide use, reduced wireworm damage, and improved income by selling at a better grade of sweet potato at harvest. Proper crop rotations and early season insecticide control measures are both very important in the overall management of wireworm.

Dr. Norm Leppla and Robert Hochmuth have secured grant funding in 2015 from the Southern IPM Center Enhancement Grants program to continue this important work. This project is funding senior-level UF/IFAS Doctor of Plant Medicine (DPM) student, Chris Kerr. Chris will coordinate field work to survey sweet potatoes for all insect pests and to focus on predictive measures to better assess wireworm populations in commercial fields.