Proper soil fertility is one of the key factors in maximizing forage production in pastures. Soil testing every 3 years is necessary to identify nutrient deficiencies. While important to supply the plant with nutrients necessary for growth, the application of excess nutrients can be expensive and may lead to environmental pollution. Several laboratories offer soil analysis, including the Univ. of Minnesota (soiltest.cfans.umn.edu).
Plants have specific nutrient requirements for growth. Without these nutrients, plant productivity can be significantly reduced. Of the nutrients required by plants, some are required in greater amounts and are referred to as macronutrients. Macronutrients include, but are not limited to, nitrogen (N), phosphorus (P), and potassium (K). Recommendations for P and K are based on soil nutrient analysis and are specific to each pasture. Basic soil tests do not measure soil N because of its rapid mobility in the soil. Therefore, N recommendations for grass pastures in Minnesota are 90 pound of N/acre per year. This amount of N is needed every year, while P and K needs will depend on soil analysis results.
By law, the nutrient content of fertilizers must be listed on the packaging. This information is often listed in the form of a three number code. For example, a product labeled as 10″20″5 would contain 10% N, 20% P2O5 (phosphorus) and 5% K2O. (potassium) Spreading 50 lbs of this product per acre would result in an application of 5 lbs N (50 lbs x 0.10 = 5 lb), 10 lbs P2O5, and 2.5 lbs K2O per acre.
The timing of fertilizer application should match the growth pattern of the forage, making nutrients available to the plants when they’re most needed. Cool season grasses (i.e. bluegrass, orchardgrass, bromegrass) and legumes (i.e. alfalfa, clover) growth is greatest during the spring and fall; therefore, a split application is recommended. Fertilizer application in early spring (i.e. April/ May) helps boost summer production, while application in early summer (i.e. mid”June) helps boost fall production. For split applications, it is recommended to divide the total amount of fertilizer needed into two applications, applying half in spring and the remaining half in early summer.
Granular fertilizer is typically spread using a broadcast spreader. For smaller pastures, walk”behind spreaders or those pulled by a garden tractor or attached to an ATV are ideal. It’s best to apply fertilizer just prior to a light rain to help dissolve the fertilizer and move it into the plant root zone. Fertilizer should not be spread in areas with standing water or near lakes, ponds or streams.
Following application, it will be necessary to restrict horse access to the fertilized pasture to prevent horses from inadvertently consuming the fertilizer. Restrict horse access until at least 1â„2 inch of rainfall has fallen, for 2″3 weeks (in the absence of rainfall), or until the fertilizer is no longer visible on the soil surface. Once the fertilizer is no longer visible, it is safe to resume grazing.
By: Krishona Martinson, PhD, University of Minnesota,