Watermelon growers typically apply a complete analysis fertilizer in the bed before before the beds are covered with plastic mulch and drip tape, well before planting. This bed fertilizer supplies a portion of the crop’s nitrogen needs, with the remainder applied through fertigation as the crop grows.

But how much nitrogen should growers commit before planting? A 2026 on-farm comparison in Levy County helped us take a closer look at the question.

How the Field Comparison Worked

The grower divided a 34-acre watermelon field into two 17-acre sections, North and South. Both sections received almost the same amount of nitrogen through fertigation. The main difference was the amount of nitrogen supplied through the complete analysis dry fertilizer placed in the bed before planting.

North received 83 pounds of nitrogen per acre from the bed fertilizer and the South received only 28 pounds. Therefore, North started the season with about 55 more pounds of nitrogen per acre in the bed.

By the end of the season, North had received 184.5 pounds of nitrogen per acre. South had received 129.4 pounds. Both sections received about 101 pounds of nitrogen per acre through fertigation. Nearly all the difference came from the nitrogen in the fertilizer applied before planting.

What Happened to the crop?

Weekly petiole-sap tests showed adequate to high nitrogen levels in both sections during most of the season. North NO3-N readings ranged from 980 to 1,500 ppm. South readings ranged from 970 to 1,600 ppm. The higher bed fertilizer rate gave no advantage in sap nitrogen levels.

The measured yields told a similar story to the petiole sap levels. Across two selected harvest areas, North produced 13,072 lb/row-acre, while South produced 13,362 lb/row-acre. Because this was an on-farm comparison rather than a replicated research trial, the results should not be considered a statistical test. However, they do support the observation that South achieved a comparable yield while receiving less nitrogen fertilizer. 

What the Results Suggest

The data from the South side of the field stands out because it maintained similar petiole-sap nutrient levels and produced the same measured yield. The South side also received about 55 less pounds of nitrogen per acre.

This comparison cannot show exactly what happened to the extra nitrogen on the North side. The crop may have taken up some nitrogen earlier. Rainfall or irrigation may have moved some below the active root zone. Still, under this field’s conditions, the extra bed fertilizer offered no measurable advantage in sap nitrogen or yield.

Connecting the Field to the 4Rs

This comparison shows why nutrient management involves more than asking, “How much fertilizer are we using?”

The 4R Nutrient Management framework focuses on the Right Source, Right Rate, Right Time, and Right Place. These principles help producers support crop production and farm profitability. They also help reduce nutrient loss and improve long-term sustainability.

In this case, Right Rate and Right Time deserve special attention.

Using Fertigation and Sap Testing

Growers commit nitrogen when they place it in the bed before planting. Fertigation offers more flexibility because growers can supply nitrogen in smaller amounts as the crop develops. Petiole-sap tests can then show whether the crop is receiving enough nitrogen.

The point is not simply to apply less fertilizer.

The goal is to apply the right amount of nitrogen at the right time and place. A producer might reduce some bed nitrogen, monitor the crop with petiole-sap tests, and add nitrogen through fertigation as needed. This approach may improve nutrient-use efficiency without reducing production.

Learning Through On-Farm Comparisons

On-farm trials and demonstrations are where cooperation between Extension agents and producers can become a valuable experience for both parties. One on-farm comparison cannot provide all the final answers. However, it can help Extension agents and growers ask better questions, make thoughtful changes, and evaluate those changes in the next crop.

Improving nutrient management does not always require a completely different practice. Sometimes it means fine-tuning a practice we already use.

Authors: Elizabeth Cannon, Mark Warren, Kelsey Crain, and Robert Hochmuth

University of Florida, Institute of Food and Agricultural Sciences; North Florida Research and Education Center – Suwanee Valley

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