Fertilizing using nitrogen (N) only:

• Nitrogen is needed by plants in large quantities. The general nitrogen (N) recommendation for vegetable crops is 2 lbs. per 1,000 square feet or 0.20 lbs. (3.2 ounces) per 100 sq. ft.
• “Heavy feeders” like tomato, broccoli, and beet (see below) should receive 3 lbs. of N per 1,000 square feet or 0.30 lbs. (4.8 ounces) per 100 sq. ft.

• High nitrogen organic fertilizers include cottonseed meal (6-2-1), nitrate of soda (15-0-0), calcium nitrate (16-0-0), blood meal (12-0-0), and fish meal (8-10% N) and fish emulsion (5% N).
• Example of an N fertilizer calculation: How do I apply 3.2 ounces of N per 100 sq. ft. using nitrate of soda (15-0-0)?
  3.2 ounces of N ÷ 0.15 (the % of N in nitrate of soda) = 21.33 ounces (1.33 lbs.) of nitrate of soda.
• How to convert a synthetic (chemical) fertilizer recommendation for organic fertilizer

Example: the recommendation is to apply 2 lbs. of N per 1,000 sq. ft. by applying 4.35 lbs. of urea fertilizer (46-0-0). You want to substitute cottonseed meal (6-2-1).

Solution #1: Divide the percentage of N in the synthetic fertilizer by the percentage of N in the organic fertilizer and multiply by 4.35 (amount of urea recommended):
0.46 ÷ 0.06 X 4.35 = 33.3 lbs. of cottonseed meal per 1,000 sq. ft.

Solution #2: Calculate the amount of fertilizer product needed by dividing the pounds of N needed by the percentage of N in the product:
2.0 ÷ by 0.06 = 33.3 lbs. of cottonseed meal fertilizer per 1,000 sq. ft. If your garden is 500 sq. ft. you would apply ½ the amount.

An excerpt from the article “Fertilizing Vegetables“, by Jon Traunfeld, Director HGIC, Extension Specialist, Fruits, and Vegetablescourtesy of the University of Maryland.