Inorganic Fertilizers

SELECTING A FERTILIZER

The numbers on a fertilizer label refer to the concentration (percent) of three major
nutrients in the material:

nitrogen (or N)
phosphate (or P2O5)
and potash (or K2O).

For example, a 25-3-5 fertilizer contains 25% nitrogen, 3% phosphate (P2O5), and 5%
potash (K2O). This means that 4 pounds of 25-3-5 would supply 1 pound of nitrogen (4 x 0.25),
0.12 pound of phosphate (4 x 0.03), and 0.2 pound of potash (4 x 0.05).

Other common fertilizer formulations are listed below. Fertilizer labels have been standardized so that the concentrations of nitrogen, phosphate, and potash always appear in the same order on the front of the package. Other components such as iron, zinc, or sulfur may be specified elsewhere on the label.

The variety of fertilizers on the market means the gardener can find a product to meet any need. Minimize the application of nutrients listed as adequate, high, or excessive on a soil test
report. Further application of fertilizers containing these nutrients may create an imbalance and reduce plant growth. If you have a soil test made and the test report recommends only nitrogen, use ammonium nitrate (34-0-0), ammonium sulfate (21-0-0), or another fertilizer high in nitrogen. If nitrogen and phosphorus are recommended, use a fertilizer such as 30-10-0. Assume for example that a soil test report recommends 2 pounds (lbs) of nitrogen and 1 pound of phosphate per 1000 square feet. Using the 20-27-5 formulation would result in the over-application of phosphate, while the 30-10-0 formulation would slightly under-apply phosphate. The gardener may decide to apply 20-27-5 for one year and build up soil phosphorus levels, then retest the soil and switch to a nitrogen-only fertilizer in subsequent years.

Alternatively 34-0-0 or 21-0-0 could be applied to meet the nitrogen requirement and 0-45-0 to meet the phosphorus requirement. Annual nitrogen recommendations for landscape and garden plants.

Plants...................... General requirements ............recommendation
Ornamentals Low: xeriscapes, natural areas........ 0 to 1 pound of nitrogen/1000 sq ft
Intermediate: standard landscapes........................1 to 2 pounds of nitrogen/1000 sq ft
High: flower beds, new landscapes........................ 2 to 4 pounds of nitrogen/1000 sq ft

Turf* Low maintenance.......................................... 0 to 1 pound of nitrogen/1000 sq ft
Intermediate maintenance..................................... 2 to 3 pounds of nitrogen/1000 sq ft
High maintenance.....................................................4 to 6 pounds of nitrogen/1000 sq ft

Vegetables** Low: peas, beans ..............................1 to 2 pounds of nitrogen/1000 sq ft
Intermediate: asparagus, beet, carrot,
melon, cauliflower, broccoli, brussels
sprouts, celery, pepper, tomato,
lettuce, radish, spinach, turnip, squash,
pumpkins
.......................................................................................2 to 3 pounds of nitrogen/1000 sq ft
High: onion, sweet corn, potato................................ 4 to 6 pounds of nitrogen/1000 sq ft

*Split the total amount of nitrogen into two or more separate applications made over the growing season. To prevent burning do not apply more than 1 ½ pounds of nitrogen/1000 sq feet in a single application.

**For high nitrogen requirement vegetables, apply the intermediate recommendation before planting, then broadcast or band additional nitrogen after plants are well established (see text under fertilizer application methods).

Name.............................Fertilizer label (Nitrogen-Phosphate-Potash)
Single nutrient fertilizers
Ammonium nitrate............ 34-0-0
Ammonium sulfate .............21-0-0
Urea..................................... 46-0-0
Triple superphosphate....... 0-45-0
Potassium chloride.............. 0-0-60

Multi-nutrient fertilizers
Ammonium phosphate....... 11-52-0 or 18-46-0
Turf fertilizer ......................30-10-0
Lawn fertilizer..................... 29-3-4
Lawn food............................ 25-3-5
Turf builder......................... 32-3-2
Starter fertilizer.................. 20-27-5
Winterizer............................ 22-4-14
Balanced fertilizer............... 16-16-16

Special purpose fertilizers
Vegetable food.................... 12-12-12
Rose food .............................20-10-5
Acidic fertilizer................... 30-10-10

Fertilizers vary considerably in price. The cost of different fertilizers should be compared
on a per pound of nutrient basis. Cost per pound depends on the package price, weight, and
nutrient concentration in the fertilizer. For example, if a 36 lb bag of 29-3-4 cost $15.88 and a 20 lb bag of 21-0-0 cost $2.99, which is the least expensive source of nitrogen? The cost per pound of nitrogen is $1.52 for the 29-3-4 and $0.71 for the 21-0-0.

More expensive fertilizers often contain pesticides for weed or insect control, and may have added micronutrients or slow release characteristics. Compare prices among products and purchase fertilizers with special additives only if they are needed.

Most fertilizers containing herbicides are meant to be used on turf and will stress ornamental trees and shrubs, and kill most vegetables and flowers. Read and follow label instructions carefully when using fertilizers containing pesticides.

FERTILIZER RATE CALCULATIONS
Nutrient recommendations for gardens and landscapes are expressed in pounds per 1000
square feet. Calculate the amount of fertilizer needed by using the soil test
nutrient recommendation If you have had your soil tested, the concentration of nutrients in the fertilizer selected, and the size of the area fertilized.

Garden and landscape areas are usually different than 1000 square feet. Estimate the size of the area to be fertilized by pacing or using a measuring tape to determine the length and width. Multiply the length by the width to calculate area. A simple formula used to calculate the amount of fertilizer required to meet a nutrient recommendation is:

Fertilizer needed ’ X lbs of nutrient 1000 sq. feet × 1 lb fertilizer Y lb nutrient × Z sq. feet area

where X is the nutrient recommendation from a soil test report in lbs/1000 sq ft, Y is the percent of the nutrient in the fertilizer divided by 100, and Z is the square footage of the area to be fertilized.

Example: A gardener is using ammonium nitrate (34-0-0) fertilizer to supply 2 pounds of
nitrogen per 1000 square feet. The garden area is 1400 square feet. How much 34-0-0 fertilizer is required in this situation? Answer: In the above equation, X is 2 pounds, Y is 0.34 (34% divided by 100), and Z is 1400 square feet.

Entering these numbers into the equation above gives an answer of 8.2 pounds of 34-0-0 fertilizer for the garden. A helpful conversion for fertilizers is 1 pint volume equals approximately 1 pound of dry fertilizer. The amount of fertilizer calculated in the above example may not seem like much when spread over a large area.

For ease of use and keep transportation costs low, inorganic fertilizers are manufactured as highly concentrated sources of nutrients. This means that applicators need to accurately calculate and apply fertilizers at the appropriate rates to supply the correct amount of plant nutrients without damaging plants or causing adverse environmental effects.

FERTILIZER APPLICATION METHODS
Fertilizers may be broadcast on the surface then tilled or watered into soil, or banded on or
beneath the soil surface. Broadcasting is efficient and often the method of choice in
areas with perennial plants. Two main types of broadcast applicators are available: the rotary
spreader and the drop spreader. Drop spreaders can uniformly apply a wide range of
fertilizer rates; however, the path of spread is limited to the width of the unit (normally 18 inches to 3 feet for low cost units).

Rotary spreaders broadcast fertilizer in a 10 to 20 foot wide path with less uniformity and rate control than drop spreaders. Either spreader type will work well for homeowners if properly calibrated and operated.

Ammonium nitrate (34-0-0) applied at the rate of 2 lbs nitrogen per 1000 square feet broadcast on the soil surface or banded in rows with 24 inch spacing.

Rotary and drop fertilizer spreaders.
Fertilizers and rates of application. Spreader manufacturers often list calibration settings for
specific fertilizers. Likewise, many fertilizer manufacturers list settings for specific spreader
models. Since manufacturers cannot list calibration settings for all situations, it is good
practice to calibrate the unit for your use. Set the spreader to the closest manufacturer’s setting for the rate and type of fertilizer you will apply. Place 2 pints of kitty litter in the unit and spread in a continuous straight path. Note the width of the spread path and the distance traveled to broadcast the litter. Calculate the rate of application (assuming 1 pint of litter equals 1 pound of fertilizer) and compare this to the rate needed. For example, if a rotary spreader broadcasts a 10 foot wide path and you traveled 40 feet to empty 2 pints of litter from the hopper, the rate of application would be equivalent to 2 pounds per 400 square feet (10 ft x 40 ft), or 5 lbs/1000 square feet. If a different rate is needed the spreader setting should be changed and the unit calibrated again. Once a spreader is calibrated for a specific rate keep a record of the setting for future use. Avoid streaking caused by fertilizer skips and overlap by applying one-half of the
calculated rate while traveling in one direction and the remaining one-half while traveling in a
perpendicular direction. This method of application is especially useful for turf fertilization
where streaking is common.

Banding is a convenient way to make in-season fertilizer applications to high nitrogen requiring vegetables like corn. To band fertilizer first calculate the amount needed for an area as if you were going to broadcast the material. Divide this amount by the number of plant rows in the area to determine the amount of fertilizer to apply in each row. Make narrow furrows 8 to 10 inches away from the base of the plants, 2 to 3 inches deep. Distribute the fertilizer evenly in the furrow and cover with soil. Foliar applications can be made with any water-soluble product and are commonly used for applying small amounts of micronutrients such as iron and zinc. There is potential for foliar burning with sprays so follow product label instructions carefully. A 2% fertilizer solution by weight is generally safe for use as a foliar spray. Mix a 2% solution by adding 0.15 lb (approximately 1.25 fluid ounces or 2 ½ tablespoons) fertilizer per gallon of water. Apply foliar sprays early in the morning or late in the evening to minimize leaf burning. Thoroughly cover foliage with the spray solution.