The amount of nitrogen fertilizer required by turf depends on various management and environmental/management factors (Table 1). A good rule to follow is to never apply more than 1.0 lb N/1000ft2 in any one application. Do not apply fertilizer more frequently than once monthly at a 1.0 lb N/1000ft2 unless you are establishing a new lawn or managing an athletic field.
The timing of N fertilizer applications depends on the lawn species. Cool-season turfgrass species such as Kentucky bluegrass, perennial ryegrass, fine fescues, and tall fescue should be fertilized mainly in the fall. A fertilization in September, November, and an application in the spring after the flush of growth (late April or May) will result in a healthy turf. Avoid fertilizing too aggressively in the summer months because of increased risk of disease. Lawns damaged during summer months and newly seeded lawns may need an additional N fertilizer application in October to help with recovery and establishment. Warm-season turfgrasses such as bermudagrass and zoysiagrass should be fertilized in the summer months when they are actively growing.
Several factors may influence how much nitrogen is applied or how many applications of nitrogen containing fertilizers are made. Below is an explanation of those factors which will help you to fine-tune your fertilizer program for the area you are maintaining.
Table 3. Factors that influence annual nitrogen applications.
|
Quality and Expectations |
Adjustment of nitrogen application rate/frequency |
|
Age of the turf (or soil) |
Typically, less nitrogen is needed on lawns that have been well-maintained for many years. |
|
Clipping removal |
Returning clippings causes an annual increase of about 1.0 lb N/1000ft2/year. Therefore, it is recommended that you return clippings. If clippings are removed, N fertilization should be increased. |
|
Use (traffic) |
Fertilization should be increased in heavily trafficked areas in order to help the turf recover from traffic injury. |
|
Irrigation |
Irrigation increases plant growth. Irrigated lawns may need some additional fertilization. Do not over irrigate. |
|
Species and cultivar |
Tall fescue requires about 33% less nitrogen fertilization than Kentucky bluegrass. Zoysiagrass requires about 50% less nitrogen to maintain than bermudagrass. |
|
Climatic conditions (weather) |
If weather is not favorable to turfgrass growth, less fertilizer will be needed or fertilization timing should be shifted |
|
Length of growing season |
If growing conditions are favorable for longer periods of time, additional fertilization may be necessary. |
|
Soil conditions (texture, cation exchange capacity) |
Sandy soils are not as capable of holding nutrients; Use slow-release fertilizers on sandy soils and increase the total annual N applied by 20%. Alternatively, soils with high quantities of organic matter (darker colored soils) need less nitrogen fertilization. Reduce the total annual N applied by 20% or more. |
|
Site specific conditions (shade, etc.) |
Turfgrass growth is reduced in shade so fertilization should also be reduced 50% in shady areas. |
|
Diseases |
Some turfgrass diseases are exacerbated by too little or too much fertilization. |
|
Recuperative needs |
Turfgrass damaged by drought stress or traffic may need additional fertilization to help recuperate. |
|
Budget |
If budget is limiting, use more frequent applications of a quick-release fertilizers at lower rates or reduce the total annual nitrogen applied. |
Which product do I use? There are many fertilizer choices available to the professional and the homeowner. Organic, inorganic, and synthetic organic products are all available. As with all plants, turfgrasses cannot tell the difference between the sources of nutrients. Some products contain high amounts of slow-release N while others contain none. Our recommendation is to use a mixture of quick and slow-release nitrogen sources in most situations. Although there are exceptions to the rule, it is good practice to use products with a greater percentage of slow-release nitrogen sources during warmer months and a greater percentage of quick-release nitrogen sources during cooler times of the year. Your soil test report will help you to choose which fertilizer might work best for your lawn. The soil test will report your soil P and K levels and also provide a N, P, and K fertilization recommendation based upon your lawn species. Common Fertilizer Terminology
-
Fertilizer Analysis: Percent composition of a fertilizer expressed as (Total N – Available P2O5 – Soluble K2O).
-
Inorganic: Does not contain carbon (ammonium nitrate, ammonium sulfate)
-
Natural organic fertilizer: Animal waste products (bone, feather, and poultry meals), manure, and activated sewage sludges.
-
Nutrient ratio: Obtained by reducing (by smallest factor) or creating a ratio of the fertilizer analysis
Examples: 28-4-4 = 7-1-1
10-10-10 = 1-1-1
16-4-8 = 4-1-2 -
Organic nitrogen fertilizer: Contains carbon (example fertilizers: urea, methylene ureas, urea formalydehyde, manure, activated sewage sludge)
-
Synthetic nitrogen fertilizer: A fertilizer manufactured from atmospheric nitrogen. These fertilizers may contain either slow-release or quick-release nitrogen forms.
-
WIN: Water Insoluble Nitrogen – An indication of the slowly water soluble (slow-release) portion of a nitrogen carrier.
-
WSN: Water Soluble Nitrogen – An indication of the readily available (quick-release) nitrogen in a fertilizer