Fall Fertility for Forage Stands - Frequently Asked Questions

 
 
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 Are there any benefits to fertilizing forage stands in the fall?
Fall fertilized stands will be able to take full advantage of early moisture from snowmelt and help alleviate the workload in the spring. In a perennial grass stand, fall application will improve the number, size, and health of tillers for the following spring. The end result could be a better first cut or an earlier turn out date on pasture. Fertilizing a portion of forage acreage in the fall also helps spread out risk should it turn dry later the following spring. An added bonus is better availability to application equipment and in some cases lower pricing.

Won't I lose all my nutrients if they sit out all winter?
While there can be losses, they are probably less than many people think. All nutrients can be lost to erosion, so take care on fields with fairly steep topography. The nutrients most at risk are nitrogen and sulfur. The main avenues of nitrogen loss are denitrification, and volatilization. Sulfur losses are primarily through leaching, particularly on coarse soils in wet years.

One of the greatest losses of fall-applied nitrogen on annual cropland can be through denitrification. If the soil becomes waterlogged, soil microbes convert nitrate to a gaseous form and it is lost to the atmosphere. Fortunately, forage stands have an established root system and numerous root channels, which enhance water infiltration and reduce waterlogged conditions. To minimize denitrification losses it is recommended that low lying areas and stands on heavy clay soils, not be fertilized in the fall.

Another concern producers have about nitrogen application is loss through ammonia volatilization (urea fertilizer is highly volatile and can be lost to the atmosphere as ammonia gas). One method to reduce these losses, albeit somewhat costly, is to band the urea (46-0-0) into the forage stand. A simpler method is to understand when volatilization losses occur and only broadcast urea when it makes sense to do so. The worst-case scenario would be to apply urea to a moist soil under warm, drying (windy) conditions. Wait until soil temperatures cool down later in September and try to apply before a good rain or early snowstorm.

To further minimize losses, keep application rates conservative. Have a soil test taken in August or early September and apply only what is called for. Be realistic with yield goals. Can that stand really yield 3 tons of hay or pasture? It may be tempting to really load up the nutrients, but like it or not, the amount of moisture you receive is going to determine yield.

When should I apply fertilizer in the fall?
Timing a fall fertilizer application usually has more to do with weather conditions than calendar date. Keep in mind that a perennial forage crop is still actively growing late in the season even though the leaves are turning color and growth seems to have ceased. Below the soil surface, root growth continues and the plants can still take up nutrients. Late September to early October probably provides the best time frame for fertilization. Apply fertilizer early enough so that there is some plant uptake and tiller development, but late enough to prevent a big flush of fall growth should it become unseasonably warm. Regardless of which type of fertilizer is chosen a timely rain or wet snowfall after application will improve the results

Which nutrients should I be applying?
It is always a good practice to do a soil test prior to fall application. Never assume that nitrogen will be the only limiting nutrient. It is equally dangerous to assume that the other nutrients will be in abundance. One of the unique quirks about a forage operation is that we tend to deplete our nutrients in some stands (selling hay) while accumulating them in others (manure on the close fields). In addition to nitrogen, forage stands also require phosphorus, potassium, and sulfur. This is especially true for a legume such as alfalfa, which can fix its own nitrogen from the atmosphere but still has a hefty requirement for the other nutrients. In a legume grass mixture it makes sense to fertilize according to legume nutrient requirements even though this may not be optimal for the grass.

Phosphorous and potassium fertilizers are not mobile so it has been a common practice to 'bank' or 'build-up' extra potassium and phosphorus when establishing new forage stands. This can be accomplished with either fertilizer or manure. In the event that phosphorus or potassium needs to be broadcast onto an established stand, an application in the fall is preferable. The frost action, moisture from snowmelt, and early rain will improve the response to these nutrients by making them available sooner than a spring application.

Sulphur is important to both legume and grass crops. Deficiencies can occur anywhere but they are especially common to the gray and dark gray soils in the parkland region of Alberta. Severely deficient forage stands should receive the readily available sulphate form of this nutrient as opposed to the elemental form. When the elemental form is used, fall application makes sense. Fall moisture and freeze-thaw cycles will help break down the sulphur granules and hasten conversion to the plant available form.


Prepared by Mark Johns, Ag-Info Centre, Alberta Agriculture & Rural Development

 
 
 
 
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For more information about the content of this document, contact the Ag-Info Centre.
This information published to the web on September 25, 2003.
Last Reviewed/Revised on September 19, 2016.