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What You Need to Know to Get the Best Regrowth After Grazing

By   /  January 12, 2015  /  1 Comment

As you read through this, you might think “DANG! This is really complex!” And you’re right it is! But that doesn’t mean you can’t figure it out. Think of it as one of those strategy games where you’re trying to maximize your points in the face of lots of variables. If you’re not good at those kinds of games, we bet you know someone who is. Just see it for the game it is, and go out and WIN!

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Plants differ in their response to grazing and harvest by height. But cultivar also plays a role, just to add a bit more challenge to your management planning.

Plants differ in their response to grazing and harvest by height. But cultivar also plays a role, just to add a bit more challenge to your management planning.

Different plants respond differently to being grazed. Knowing how, and why, can help you decide how you are going to manage your pasture and hayfields. To sum it all up, tall plants grazed short will have to rely on their roots to feed them for regrowth, but low-growing plants have leaves that will provide energy for regrowth from photosynthesis.

To quote Geoff Brink of USDA-ARS:

“Plants would prefer to grow new leaves by producing carbohydrates with old leaves than by moving stored carbohydrates. It’s easier and more efficient.”

In other words, leaving some leaves to help the plant regrow is preferred. Even though old leaves are less efficient at photosynthesis, having them around to feed the plant is more efficient than dragging stored energy out of the roots and using that.

Screenshot 2014-11-24 13.58.47To apply that concept, it helps to know which plants, grazed too short, will have bigger problems than others. One big determinant is the growing point. The graph of “Morphological Characteristics” gives you a good idea of which plants are considered tall or short. Tall plants have more regrowth problems when grazed to low. Short plants have more leaves at lower heights, so when grazed short, will still be able to depend on photosynthesis.

It is the jointed grasses, with non-flowering stems that will have to rely on energy stored in the roots as carbohydrates if grazed too short, and that’s easy to do. Think: timothy, smooth bromegrass, reed canary grass. Jointed grasses have growing points that move up the stem with regrowth. Grazing them shorter will have even more of an impact.

Screenshot 2014-11-24 13.59.11Non-jointing grasses keep their growing point at the crown, even when they are grazed. That keeps the growing point farther from the mouths of grazing livestock and blades of mowers. These include orchard grass, tall and meadow fescue, perennial rye, Kentucky bluegrass.

It gets even trickier when the breeders get involved. Orchardgrass could be thought of as a tall grass, but different orchardgrass cultivars (Topeko and Benchmark) have been bred to allow it to be grazed shorter.

Timing of the first harvest or grazing, the frequency of grazing, and the amount of pressure, can all impact the stand’s ability to recover. Picking the point of the first harvest will help determine the quality of the forage. In some cases, you might rely on boot stage, but for some species that might be too late. Sampling and knowledge of the specific species involved can help.

Screenshot 2014-11-24 14.00.13

The shorter you graze your grass, the longer it will take to grow back, and the longer you’ll have to wait to get back to that pasture again. This can be bad in the spring and summer, but good in the fall if you want to inter seed your pastures.

Screenshot 2014-11-24 13.54.55

Use this curve as a rule of thumb for helping you decide how short you can afford to graze your pastures. Notice how at a little over 6 inches, you reach a point of diminishing returns. Seems like leaving 6 inches is about the best thing you can do….but of course it depends on what you’re trying to accomplish.

The shorter you cut (or graze), the more yield you’ll get. For alfalfa, for each inch you lower the mower blades, you can expect about an extra 1/2 ton per acre per year. But that will also lower the Relative Feed Value by 5 points for every inch. Not to mention that the shorter you go, the shorter the stand life may be. The shorter plants will have a harder time recovering, and this will end up tiring out the pasture or hayfield more quickly.

Taller residual height affects regrowth rate; okay, that’s obvious.This is especially true with smooth bromegrass, and also with orchardgrass and timothy. Leaving 4″ of residue instead of 2″ means that your regrowth rate will be almost 50 lbs per acre per day, instead of just 30.   In late summer and early fall, the cool season grasses put in tillers, including reproductive tillers. Severe defoliation can set things back. Knowing this, overgrazing can be used strategically in the fall to help add new species with a spring planting into an established stand.

However you choose to graze, or harvest, knowing what you’ve got and how it grows is half the battle. Then the fun of figuring out how to best utilize it is a game of strategy.

 

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About the author

editor and contributor

Rachel's interest in sustainable agriculture and grazing has deep roots in the soil. She's been following that passion around the world, working on an ancient Nabatean farm in the Negev, and with farmers in West Africa's Niger. After returning to the US, Rachel received her M.S. and Ph.D. in agronomy and soil science from the University of Maryland. For her doctoral research, Rachel spent 3 years working with Maryland dairy farmers using management intensive grazing. She then began her work with grass farmers, a source of joy and a journey of discovery.

1 Comment

  1. Gene Schriefer says:

    We are fortunate to have Geoff Brink in Wisconsin doing this research.

    While not part of Geoff’s research on residual height, residual also helps to shade soil and maintain cooler soil temperatures in summer creating a more favorable micro-climate. We’re in a continental climate zone, cold winters, warm summer, and keeping soil (and plants) in the temperature comfort zone keeps them actively growing and reduce soil moisture loss.

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