Carrot is a relatively new and emerging crop in North Florida with about 5,000 acres grown annually in the region. The acreage increase over the past 10 years in North Florida and South Georgia is largely due to the influence of water related issues in California. Growers and packers had to search for alternate production areas where water is more abundant, fields have deep sandy soils, winter climate is relatively mild, and the production area is closer to metropolitan areas with large markets. These sets of conditions resulted in increased acreage of carrots being established by large California-based farming operations in the Suwannee Valley area of northern Florida. Carrots have a long tradition in Florida but mainly on the muck soils in central and southern regions of the Sunshine State. Since production on the deep sands of North Florida began over the last decade, nutrient management research was needed to evaluate various sources and rates of nitrogen fertilizer to determine current Best Management Practices (BMPs) for carrots grown on sandy soils. Initial research focused on various rates of conventional nitrogen fertilizer for both cello and snacking-types of carrots. This research showed the existing nitrogen rate recommended by UF/IFAS needed to be adjusted slightly upward from 175 to 200 lbs per acre, which was later approved. A complementary part of the carrot fertilizer research was evaluating the potential of polymer coated controlled release fertilizer (CRF) and this was conducted over the past 5-to-6 years.
Objectives
In this controlled release fertilizer research trial, UF researchers tested several nitrogen-release rates, various total season nitrogen rates, placement of the CRF in the soil, and timing of applications. Early trials focused on a single application of CRF in the bed prior to seeding in the fall season. This application method showed great promise, but the carrot season is long, lasting 150 or more days during periods of highly variable temperatures. Since the polymer coated fertilizers used in this study release nutrients based on temperature, it was unlikely that the polymer coated nitrogen would be released in a perfect timing over the long and variable season. As a result, the research team proposed to split the application of nitrogen to approximately half of the season’s nitrogen requirement be applied just prior to seeding followed by various combinations of conventional versus CRF nitrogen during the middle of the season. This strategy would hopefully better match the release rate of the nitrogen with the crop uptake over the season and as a result, potentially reduce nitrogen leaching losses in comparison to conventional nitrogen programs or CRF programs with all of the nitrogen at planting.
Treatments
| Treatments | Total N (lbs/ac) |
Treatment Description (2022-23) |
|---|---|---|
| 1 | 200 | Conventional N, total application 200 lbs/ac. 25 lbs/ac preplant, the remaining N applied with multiple applications during season. |
| 2 | 200 | CRF N, Total application 200 lbs/ac. All *preplant* |
| 3 | 200 | CRF N, total application 200 lbs/ac. 100 lbs/ac CRF N at preplant and 100 lbs/ac CRF N in-season once (*early ~ 45 DAP*) |
| 4 | 200 | CRF and Conventional N, total application 200 lbs/ac. 150 lbs/ac CRF N at preplant. 25 lbs/ac conventional N in-season (*twice*) |
| 5 | 175 | CRF and Conventional N, total application 175 lbs/ac. 150 lbs/ac CRF N at preplant. 25 lbs/ac conventional N in-season (*once*) |
| 6 | 200 | CRF N, total application 200 lbs/ac. 100 lbs/ac CRF N, preplant and 100 lbs/ac CRF N in-season once (*middle ~ 55 days*) |
| 7 | 200 | CRF N, total application 200 lbs/ac. 100 lbs/ac CRF N, preplant and 100 lbs/ac CRF N in-season once (*late ~ 65 DAP*) |
| 8 | 200 | CRF N, total application 200 lbs/ac. 75 lbs/ac CRF N at preplant and 125 lbs/ac CRF N in-season once (*early ~ 45 DAP*) |
Results
The results of this two-year study were summarized and recently presented at the 2024 Florida State Horticultural Society Annual Meeting. The paper was titled “Analyzing Controlled-Release Fertilizers Role in Reducing Nitrogen Leaching in Carrot Row Cropping Systems in North Florida” (by Vivek Sharma1, Robert Hochmuth2, and Shiva Bhambota1, 1-Dept. of Agricultural and Biological Engineering (ABE), University of Florida, 2-North Florida Research and Education Center, Suwannee Valley, Live Oak, FL). The data collected during the growing season included multi-depth soil samples at 0-12, 12-24, 24-36 inches, leaf tissue samples, canopy cover assessments, and soil moisture sensor data. At harvest, data was collected on carrot yield, quality characteristics, length, and diameter.
Early in the growing season, soil nitrate from CRF treatments (200 and 175 lbs/acre CRF nitrogen at panting) was significantly higher than other treatments at all soil depths. Split application of CRF (100 lbs N/acre at planting and 100 lbs N/acre at 45 days after planting (DAP) maintained the soil nitrate levels within the optimum levels throughout the growing season. Similar dynamics of soil nitrate levels were observed between split CRF treatments (second application at 45, 55, and 65 DAP) . Soil nitrate levels tended to peak after periods of rainfall and irrigation events especially at 24–36-inch depth indicating nitrate leaching. Split application of CRF (100 lbs N/acre at planting and 100 lbs N/acre at 45 DAP) maintained the soil nitrate levels within the optimum levels. Higher soil nitrate levels were observed when increasing the in season CRF levels to 125 lbs N/ac.
In both years, all treatments were at or above the current target nitrogen sufficiency range with all treatments ranging between 2.55 to 4.96%. No significant difference in leaf tissue nitrogen was found among treatments, nor was any significant difference found in carrot yield among treatments. For both years, split application of CRF treatment (100 lbs N/acre at planting and 100 lbs N/acre at 45, 55, 65 DAP) improved carrot yield. There was no significant difference in the diameter of carrot tops for all treatments, which ranged from 1.1 to 1.4 inches. The difference in the average length of carrots for all treatments was also found to be non-significant, within the range of 7.5 to 8.6 inches.
Conclusions
Polymer-coated CRF provided crops adequate N to support crop health, growth, and yields similar to that of the conventional fertilizer program in the sandy soils and the wet climate of North Florida. In both years, all treatments were at or above the current nitrogen target sufficiency range with all treatments. Split applications of CRF improved carrot growth and yield compared to single application of CRF at planting while minimizing nitrogen leaching. However, no difference in yield and yield components was observed between the CRF split application timings of treatments.
This blog was written by Sydney Williams, Bob Hochmuth, Vivek Sharma, and Shiva Bhambota, UF/IFAS North Florida Research and Education Center – Suwannee Valley .
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