Liming and Fertilizing Horse Pastures

Soil fertility is often overlooked on horse farms, but it is one of the most fundamental aspects of pasture health. You pay close attention to your horse's nutrition so it can perform its best and live a healthy life, and your pasture grasses need the same care if you want them to provide nutritious feed for your horse. Pasture plants that are deficient in nutrients may grow poorly, be discolored, or even die. However, blindly applying lime and fertilizer every year is also not the best approach for environmental and financial reasons.

The first step in any pasture improvement is proper soil testing. Take representative samples (many subsamples mixed together) of your fields and send them to a laboratory to be analyzed. For instructions, see Don't Guess, Soil Test. Soil tests should be repeated every 3 years.

The results will tell you all about your soil fertility. Specifically, they will state how much limestone (lime) you need to adjust your soil's acidity and how much fertilizer nutrients you need to feed the forages. Let's look at each of these individually.

Limestone

Lime is used when soil is too acidic for optimal plant growth. We measure acidity using the pH scale; numbers below 7 are acidic, 7 is neutral, and numbers above 7 are basic (or alkaline). Different plants grow best under different pH conditions, and pasture grasses thrive in pH 6.0-6.5. Legumes like alfalfa and clover thrive in pH 6.5-7.0. We generally try to maintain pastures around 6.5. What may seem like a small shortfall (5.8 instead of 6.5) is actually a big difference that will affect your forages. Additionally, if your soil is too acidic, then any fertilizer application will be less effective.

The soil test result will state how many pounds of lime to apply over a 3-year period. The recommended amount is not meant to be applied annually. Lime is generally needed in very large quantities, like tons per acre. Therefore, it is usually most economical to hire someone to apply this for you rather than buying it by the bag. Large chemical companies can send a lime truck to treat your fields; however, this doesn't always work out on smaller farms and pastures with narrow lanes and gates. Some companies may drop off a cart full of lime that you spread with your own tractor. Ask around to find out who your neighbors and other horse farm owners use.

Ag lime (calcium carbonate) is not toxic to horses. However, the product can be quite dusty if it is finely ground. You should leave horses inside when the product is being applied if it is dusty. A small amount of rain or even morning dew should be sufficient to reduce the dust.

Different lime products have varying quality when it comes to neutralizing soil acidity. The product will have a number on the label: Calcium Carbonate Equivalent, or CCE. This number standardizes how effective the product is, compared to pure calcium carbonate (100%). A product with CCE below 100% will be less effective and require more product for the same result. A product with CCE above 100% will be more effective and require less product for the same result. A similar number is Effective Neutralizing Value (ENV), which also considers the fineness of the lime material. Read more about lime and CCE here: Soil Acidity and Aglime.

Lime can take a long time to neutralize soil acidity, especially when it is not finely ground and when it is not mixed into the soil. It can take 6-12 months for surface-applied lime to do its job in the root zone of grasses! However, it is one of the most cost-effective ways to improve a pasture with low soil pH.

Pelletized lime is gaining popularity because it is easier to apply with traditional fertilizer spreaders than pulverized lime, which is a fine powder. Pelletized lime is finely ground limestone mixed with a binding agent to form pellets that break down in the soil. It is more expensive than bulk ag lime. Because the lime is so finely ground, it reacts quickly in the soil, but the neutralizing effect does not last as long. Therefore, pelletized lime can be applied in smaller amounts more frequently than ag lime. However, the same total amount of lime is needed over the 3-year period covered by the soil test.

Fertilizer

Plants need fertilizer nutrients to grow and be productive. Nutrient levels in the soil may decline over time as the plants remove nutrients to be incorporated into grass, then grazing animals remove the grass and use the nutrients for their own bodies. Fertilization replaces the nutrients that were removed. Manure can also replace some of these nutrients, but not in an even pattern and not in the ratio that plants need.

The soil test results will tell you how many pounds of nitrogen (N), phosphate (P₂O₅), and potassium oxide (K₂O) need to be applied to each field annually. Pounds of each nutrient is not the same as pounds of fertilizer, as different fertilizer products will contain different percentages of each nutrient.

If you are hiring someone to apply fertilizer for you, they should be able to read your soil test report and select a product(s) and amount that will meet the recommendations. If you want to DIY, then you will need to do some math or contact your local Extension educator.

A fertilizer product will have a grade (or a guaranteed analysis) on the bag. It is a series of 3 numbers separated by dashes, like 10-10-10. These three numbers tell you how much N, P₂O₅, and K₂O are in the product by weight. Therefore, a 50-lb bag of 10-10-10 fertilizer contains 5 pounds each (10% of the 50-pound bag) of N, P₂O₅, and K₂O. It would take a lot of bags to apply 50 pounds per acre of nitrogen (a common springtime recommendation) to a pasture! For example, a 2-acre pasture would need 20 bags of this product to provide 50 pounds N/acre.

Fertilizer products used by farmers often have higher concentrations of these nutrients, such as diammonium phosphate, which has a guaranteed analysis of 18-46-0. These products can be blended to create a custom fertilizer to match your field’s needs. Even organic fertilizers should have a guaranteed analysis to guide application.

There are a few things to know about each nutrient.

• Nitrogen: This nutrient causes a flush of leafy growth in grasses and is an essential component of chlorophyll and proteins. Legumes like clover produce their own nitrogen in root nodules, and applying N fertilizer to a field with both legumes and grasses can favor grass growth. Nitrogen can only be used by the plant when it is actively growing, so it would be a waste to apply it in winter or hot, dry summer months (in Pennsylvania) when grasses have limited growth. The recommended amount is based solely on expected forage yield (a field on the submission form) and is intended to be split into two (or three) applications: one in spring (maybe one in summer if soil moisture is adequate) and one in fall. Do not apply the whole amount at once!
• Phosphorus: This nutrient is important to many plant processes, especially root and seedling growth. If you plan on seeding new grass, it's important to make sure your soil phosphorus is in the optimal range. It can be applied any time during the growing season, and whatever doesn't get used by plants builds up in the soil over time.
• Potassium: This nutrient is also vital to many plant systems and is especially important for winter hardiness. Like phosphorus, it can be applied at any time during the growing season. Potash refers to potassium-containing fertilizer compounds. If you graze ruminants, you may be familiar with grass tetany, which can occur when soils and forages are very high in potassium, causing a magnesium deficiency in animals. This does not occur in horses.

You should leave horses off the treated fields until about ½-inch of rain has fallen to wash the product off the plant leaves. Fertilizer can be applied as a granular or liquid product. Cone-shaped spinner spreaders are a common way to apply dry fertilizer and can be pulled behind a tractor or other farm vehicle. Make sure to calibrate your equipment before applying fertilizer to make sure you are applying at the rate you expect!

It is possible to estimate the nutrients provided by manure dropped by grazing animals and subtract that from your fertilizer needs. 

Hiring A Lime or Fertilizer Applicator

Sometimes, the hardest part of this process is finding someone to apply the materials for you. You may find some chemical companies that can help you by searching for "agricultural fertilizer," but they may prioritize larger crop farms and have trouble accessing small pastures with their large equipment. Word of mouth tends to be the most effective option locally. Ask your neighbors and other nearby horse farm owners who they use. Ask around at ag supply stores or even on social media in local equestrian groups.

Take-Home Messages

If you are looking to improve your pasture quality and provide more forage for your horses, addressing soil fertility needs is the first step. There is a lot to know, but these are the basics:

• Soil test every 3 years
• Lime according to test results, the recommended amount is meant to be applied once per 3 years
• Fertilize annually according to the test results:
  • Nitrogen: Split the application into two and apply half in the spring and half in the fall
  • Phosphorus: Apply any time during the growing season
  • Potassium: Apply any time during the growing season

Your local Extension office can help you obtain soil test kits, fill out the submission form, and interpret the results. Don't hesitate to call with any questions about soil testing!