Herbicides and fertilisers: Wise investments for horse pasture management


Know your weeds and how to deal with them. That is the advice to horse owners seeking to effectively manage their pasture.

“Weed control is often misused,” Professor Ray Smith, a forage specialist, told those attending a recent Pastures Please!! workshop in Kentucky.

“You want to make sure you know what weeds are there, and spray for the ones that are there,” Smith told those attending the virtual workshop.

“Some herbicides have good residual control, meaning they control weeds even after spraying. Others don’t last very long. But the unintended consequence of killing weeds is you have bare soil, and then you need to do something to cover that bare soil.

“So, you’ve got to be very careful with what herbicide you use because they have different wait periods before reseeding.”

Smith was joined by Krista Lea, a plant and soil research analyst with the university, for a discussion on wise investments for pasture management.

The discussion highlighted the steps to take in order to evaluate pastures and get the best use out of them.

While weed control and management is a useful tactic, it is not the answer to all pasture problems. Photo: University of Kentucky

Smith detailed how management practices such as weed control, use of fertilizers, nitrogen, overseeding and pasture resting can improve a pasture.

He began with weed control, sharing an image of a pasture full of flowering buttercup. Smith pointed out that by the time weeds get to that point, it is too late to use herbicides or to manage them effectively.

The average range for the cost of herbicides in the United States is $12 to $25 per acre.

Smith indicated that if weeds are rampant in a pasture, this is a small price to pay to help lessen the burden. When weeds are minimal, then the best recommendation is patience and good grazing management.

While weed control and management is a useful tactic, it is not the answer to all pasture problems. Other issues, such as low nutrient density, should be managed in other ways.

If other forage is available, grazing horses will usually avoid buttercup because the leaves, flowers and stems have a sharp, acrid taste.
If other forage is available, grazing horses will usually avoid buttercup because the leaves, flowers and stems have a sharp, acrid taste. © Dr Jimmy Henning / University of Kentucky

One of the ways that Smith encourages nutrient management is through the use of fertilizer.

“Fertilizer is often misunderstood, in how to apply the fertilizer and when you need to apply the fertilizer,” Smith said.

“When I’m talking about fertilizer in this context, I’m going to talk about particularly in Kentucky, applying lime to change the pH, applying phosphorus and applying potassium.

“So, the real value of applying those nutrients is maximizing the production and also the stand life. It is safe to apply fertilizers and these particular products when the horses are on the field.”

Using the fertilizers Smith mentioned can cost up to $65 per acre in the US.

For the best results, Smith recommended a soil test be conducted to indicate what is needed so as to not overdo the concentration of a particular nutrient. Pastures should be soil tested every two to three years in order to accurately treat the pasture.

Fertilizers may be applied any time of the year, except when the land is wet.

“You can’t fertilize your way out of poor management,” Smith said, meaning overgrazing and poor upkeep of pastures cannot be fixed with fertilizer.

Nitrogen, while a fertilizer, is its own entity for the purpose of pasture management. The use of it increases yield. Fall application of nitrogen is recommended and encourages leafy growth, strong roots and early spring growth.

Early spring application boosts newly planting seedlings and helps develop overgrazed pastures, but can result in excess pasture growth and more mowing. But it is important to remember that nitrogen is beneficial to all plant species, including weeds, so be judicious in the amount of nitrogen applied. The average cost of nitrogen is $23 per acre.

Smith addressed overseeding as an effective pasture management tool, but one that is often poorly executed. Overseeding allows for growth to occur in bare areas which, in turn, prevents weed growth. Timing and resting the growth is critical to development of the plants.

Smith stressed the importance of resting pastures.

“Resting allows grasses to rebuild leaves and roots after grazing, increases stand life, increases forage quality, favors grasses over weeds, reduces soil erosion and nutrient leaching and the pasture looks better. And the cost of rest is free.”

Pastures need to be rested in order to allow existing grasses to regrow leaves and restore carbohydrate reserves in long-term survival, according to Smith.

Seedlings, in particular, are vulnerable to close grazing consistent hoof traffic. Allowing pasture an opportunity to rest also encourages improved forage production, which permits the feeding of less hay and grain.

Smith used images of experiments to further convey his point. The comparisons between rested pasture and continuously grazed pasture growth show that resting is beneficial for plant growth. To properly rest a pasture, it should be grazed down to 3-4 inches, and then mowed if the pasture is uneven. Horses should be relocated off the pasture for two to four weeks in order to regrow about 8-10 inches of forage. After this, the horses may be returned to grazing in the pasture. Rotational grazing is a great method to allow resting time.

For all of the pasture management practices that Smith discussed, the total cost would be about $153 per acre, done every three years. By doing this, the amount of usable forage in a pasture may be doubled.

Article courtesy University of Kentucky College of Agriculture, Food and Environment.

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