Applying fertilizers to hay and pasture fields to stimulate plant growth will generally increase yields substantially.
This is a sound management practice if application is made in accordance with soil test results and or expected harvest yields.
Applying more nutrients than recommended from a soil test can be expensive and detrimental to the environment. A single application of 12-12-12, 15-15-15, or 19-19-19 fertilizer on each field year after year does not make good use of your purchased nutrients. Why? Nutrient levels in the soil may be different in each field and grasses and legumes need nutrients in different quantities for maximum growth.
Legume plants do not need the same amount of nitrogen as grass plants. Also, different amounts of each nutrient (phosphorus and potassium) are removed in each ton of forage harvested.
Put them back. For example, in meadows, each ton of tall grass or legume forage harvested removes approximately 13 pounds of phosphorus and 50 pounds of potassium from the soil. That means these nutrients need to be replaced, preferably in the ratio of about one part phosphorus to four parts potassium.
A single yearly application of fertilizer, as mentioned above, would not build soil nutrients in the proper ratio to offset those removed in the forage.
If we expect to harvest 4 tons of hay per year from each acre, we would remove 52 pounds of actual phosphorus and 200 pounds of actual potassium from the soil on each acre.
Applying 275 pounds of 19-19-19 fertilizer per acre would meet our phosphorus needs (275 x .19 = 52 lbs.), but it would be about 148 pounds short of the potassium we need to replace. An additional application of 250 pounds of potash (0-0-60) per acre should be applied to maintain our nutrient balance.
Phosphorus and potassium may be applied any time of the year if soil conditions are firm enough to hold equipment, but after first cutting has been removed may be the best time.
Our 275-pound application of 19-19-19 fertilizer would also contain 52 pounds of nitrogen per acre, adequate maybe for grass stands in one application, but too much nitrogen for a predominately legume stand. That is why split or multiple applications of blended fertilizer with the appropriate analysis should be made.
Maximize growth. Multiple applications made during the growing season are an effective method to maximize growth and reduce nitrogen losses. One should use split applications if you have sandy soils with high potential for leaching, if you run the risk of volatilization of nitrogen, or if high rates of fertilizer are to be used.
Surface volatilization occurs in some forms of nitrogen when it breaks down and forms ammonia gases. The rate of surface volatilization depends on moisture level, temperature and pH of the soil surface.
If the area is wet when a fertilizer is spread and additional rain is not soon expected, evaporating water can pick up the ammonia released from the urea and be lost. Temperatures greater than 50 degrees Fahrenheit and pH’s greater than 6.5 can significantly increase the rate of urea conversion to ammonia gasses.
Do not apply urea-based fertilizers to the surface of fields that have been limed within the last three months, especially if 2 or more tons of lime per acre was applied, unless the fertilizer is incorporated, because nitrogen loss will occur.
To stop ammonia volatilization from urea, the urea must be tied up by the soil. To get urea in direct contact with soil, it is beneficial to have enough rain to wash the urea from plant residue into the soil.
If residue is very light, .25 to .5 inches of rain is enough to dissolve the urea and wash it into the soil. If heavy plant residue covers the soil, .5 inches or greater rainfall is required.
Other forms of nitrogen such as ammonium sulfate or ammonium nitrate could be used to reduce volatilization, but may be hard to find unless you make special purchasing arrangements.
Pastures. Grasses and legumes in a pasture require the same nutrients as those in meadows. Do you need to put as much fertilizer on your pastures as you do your hay fields? Probably not, because as cows consume forages they also return approximately 66 percent of the phosphorus and 92 percent of the potassium to the field in their manure.
Are the nutrients evenly distributed back on the pasture? This depends a great deal on your management. When cows are confined to a specific area for a short period of time and rotationally grazed, studies have shown manure deposits to be evenly distributed over the entire area.
If cows are continuously allowed to roam over large areas as they choose, manure deposits (your nutrients), are moved to the loafing areas where the herd spends most of the day. This may be around watering troughs or in a tree line/woods.
Fertilizer applications in pastures should be done at times determined by your livestock’s forage needs. If you need additional forage early in the spring, fertilizing up to one-third of your pastures may be needed.
Generally, grass and legume forages grow quickly in the spring (spring flush) without additional fertilizers. Early spring fertilization in pastures may compound problems associated with spring grass growth, such as grass tetany. Early to mid-June is usually a better time to spread fertilizer on pastures to boost production before hot, dry weather arrives.
Many farm managers also make fertilizer applications to a portion of their pastures again in early August, then remove the livestock. This allows them to stockpile the forage growth for use later in the fall and winter to reduce stored feed needs.
So what does all this mean? Usually a specific blend of nutrients and proper timing of application are needed in most fields to maximize production. In most cases this requires a soil test and planning for the application to be done at a time you will not loose a large portion of the nitrogen to volatilization.
More than once. Multiple applications may be warranted to make the best use of the nutrients. Cost of nutrients must also be considered when trying to determine the best fertilizer to use.
Randomly spreading fertilizer nutrients is kind of like using a road map when you don’t know where you are going. You can see different routes going many different places, but if you don’t know where you are going you can’t choose the best route to get there.
For more information stop by your local extension office and ask for the OSU Agronomy Guide, Bulletin 472. This bulletin has chapters that discuss production practices, fertilization and lime recommendations for forage crops.
(The author is an OSU Extension Agriculture and Natural Resources Extension Educator in Monroe County, Ohio. Questions or comments can be sent in care of Farm and Dairy, P.O. Box 38, Salem OH 44460.)