Vegetable Garden: Fertilization: Nitrogen Application

Soil fertilization is the addition of soil nutrients to support crop growth. While some soil amendments add small amounts of nutrients, amending the soil to improve soil tilth is not the same as amending the soil to provide nutrients. Manufactured fertilizers are popular with gardeners because they are readily available, inexpensive, easy to apply, and generally provide a quick release of nutrients for plant growth. Application rates for any fertilizer depend on the content and the amount of nutrient to be applied. In products containing multiple nutrients, the application rate is always based on the nitrogen content.

Nitrogen is the nutrient needed in largest quantities by plants and the one most frequently applied as fertilizer. It is annually applied in the form of manufactured fertilizer, organic fertilizers, and/or organic soil amendments. Application rates are critical, because too much or too little directly impacts crop growth.

The standard annual application rate for home vegetable gardens is 2 pounds actual nitrogen per 1,000 square feet (0.2 pound actual nitrogen per 100 square feet). When organic matter is supplied, adjust the rate accordingly to account for nitrogen released by the organic matter. [Table 2]

Manufactured nitrogen fertilizer can be broadcast and watered in, or broadcast and tilled into the top few inches of soil. It can be banded 3-4” to the side of the seed or plant row. Do not place the fertilizer in the seed row or root injury will occur. Some fully soluble types are applied in the irrigation water. “Organic” nitrogen fertilizers are typically tilled in or some can be applied in irrigation water.

Table 2. Standard Nitrogen Fertilizer Application Rates for Gardens
Soil Organic Content
	Typical garden soil low in organic matter(<2% organic=”” matter=”” div=””>	Moderate level of organic matter  (2-3% organic matter)	High level of organic matter (4-5% organic matter)
Nitrogen needed	0.2 lb. actual N per 100 sq. ft.	0.1 lb actual N per 100 sq. ft	0
Fertilizer examples
Ammonium sulfate 21-0-0	1 lb. fertilizer per 100 sq. ft approx. 2 cups)	0.5 lb. fertilizer per 100 sq. ft( (approx. 1 cup)	0
OR Ammonium nitrate 34-0-0	0.6 lb. fertilizer per 100 sq. ft. (approx. 1 1/3 cups)	0.3 lb. fertilizer per 100 sq. ft (approx. 2/3 cup)	0
OR Urea 45-0-0	0.4 lb. fertilizer per 100 sq. ft. (approx. 1 cup)	0.2 lb. fertilizer per 100 sq. ft (approx. ½ cup)	0