Dennis Johnson, Dairy Production Systems – WCROC

June 18, 2005

Nature certainly throws us curves when we plan our summer of grazing for dairy animals. So far this year we had a warm early spring that got grass off to a quick start, then it turned cool and cloudy to slow the process down, and in early June rampant grass growth has been nearly impossible to keep up with. I just finished my weekly walk around the pastures at the West Central Research and Outreach Center in Morris and have lots of notes about clipping and haying. I need to make a coherent grazing plan for the next month. This is where the concept of a grazing wedge comes in.

The grazing wedge (shown below) depicts a 30 paddock rotational pasture system. This is about the right number of paddocks for providing fresh pasture each day and allowing plenty of time for healthy plant regrowth before grazing again. The columns, depicting daily rotation through paddocks, show that on any given day the paddocks will have different amounts of forage. The paddocks with the smallest supply, on the far right, were grazed as short as they should be yesterday. It is important to always leave a certain amount of forage so the plant will regrow as quickly as possible. In this example of clover/bluegrass, note that 1000 lb per acre is left as permanent base growth. On the left columns, the paddocks that had the longest rest period grew more than needed in 30 days. Therefore, the first 5 paddocks can be hayed to feed next winter, or later in the summer when forage supply is low. Thus, tomorrow we want to graze paddock 6, moving along to 7, 8, etc. as they advance to the best stage for grazing. We want to continue to graze in the space between the “too mature” line and the “permanent base growth” line. That space between these two lines is called “The Grazing Wedge”.

Keep it Between the Lines!

The Grazing Wedge (FW Owen, based on Voisin principles)

We recognize that rates of growth will not always be equal. We know that variations in rainfall, sunlight, temperature, fertility, forage species and other factors conspire to leave us with uneven growth. If there has been a period of excellent growing conditions, the grazing wedge will have a hump. When that happens there will be a time two or three weeks beforehand when we know there will be some extra hay to make. As a result, we can prepare for that.

There are also times, for example a couple of weeks without rain, when we know there will be a depression in the wedge, the wedge will be concave. But, we won’t be caught unaware of this situation because we’ve been watching the wedge. When I see that we are going to have a shortage in two or three weeks, I make a decision to increase supplement to the cows now. A few extra lbs of corn silage or hay will meet the cow’s nutritional needs and slow down the daily paddock rotation. Moving at a slower rate and providing extra supplemental feed gives the pasture extra time to grow to the proper yield. Experience has shown that speeding up the rotation or dipping into the permanent base reduces the likelihood of maintaining healthy growth later in the season. In most years you can have green grass late in the fall if you use a planning tool like the grazing wedge to keep your forages healthy through the summer.

Even though we know that nature is variable, good estimates of pasture growth are needed if we are to formulate “a good plan”. A wise old man told me to “plan, plan, plan; but alertly adjust the plan when conditions change”.

A Sticky Issue (A note on weed control for graziers)

Graziers hate thistles!! Thistles are among the few species found in our pastures that cows won’t readily turn into milk if consumed at the right stage. Graziers, and their neighbors, also hate it when electric fences short and the cows get out!! So, an easy solution is spraying the fence line with glyphosate. That should solve the electric shorting problem. But, remember there may be unintended consequences.

Plan ahead on how to manage weeds under the electric fence.

The picture to the right shows what happens when fence lines are sprayed with glyphosate, which will bare ground under the wires and when there are uncontrolled thistles in the paddock. The thistle seeds blow to the fenceline and find good growing conditions in the bare soil. As a result, the grazier is now locked into spraying the fence line. In this case, the quick and easy solution created new problems in the system. Therefore, the grazier needs to plan ahead on how to manage the weeds under the electric fence, not just automatically use an herbicide that removes all growth.