Soil Compaction Is a Sneaky Enemy By Jim Gerrish

Editor Joel Salatin commented:

This is a fantastic article. I need to put this on a billboard at the entrance of all our properties. Over the years, the biggest spats we’ve had with landlords is pugging, but those areas always show tremendous improvement (over and above adjoining paddocks) on year two. Year one is deeper-rooted weeds. Year two is timothy and clover and heavenly beauty. But when that landlord looks out and sees slurry, almost no amount of explaining  can get you back in good graces.

MAY, Idaho: As we learn more and more about the exciting world of soil biology under our feet, most of us are coming to appreciate there are amazing things happening in the soil that we don’t really get to see on a daily basis. We may see changes taking place in our pasture plant community. Our livestock may be staying healthier. We might even have a little more money in the bank.

I am as guilty as anyone for not paying enough attention to soil health and function for the first half of my life. It’s easy to get excited when you see your above-ground pastures improving every season. It is right in front of you. If you open your eyes and mind, you can see it happening. If your farm is carrying more livestock now and they are healthier, you can see it every day.

Some of the stuff that goes on below ground, we just have to take on faith because we don’t look beneath the soil surface on an every day basis. Plus, a lot of those microbes are invisible to the naked eye. There are positive things happening below ground that we can’t see unless we go looking. Sometimes all it takes is a poke with a shovel to reveal good things are happening.

There are also negative things going on below the surface that we might not notice. One of the more sinister developments that might be taking place below your feet is soil compaction sneaking up on you. From time to time we might have cattle on a pasture when a sudden storm comes up. We go out next morning and get a big shock. The sod is broken and the soil is all pugged up. It might look like the field was tilled, so we are left to think, “Boy, I probably really compacted that paddock!”

I’ve done that a good number of times over the years. What I have found is that if we move the livestock off the damaged paddock within a few hours of the trampling event, the paddock usually recovers very well. That short term impact doesn’t actually compact the soil.

It isn’t the first hoof that stomps the soil that does the real damage. It is the tenth, the twentieth, the hundredth that we need to be concerned with. There are three factors that determine the extent of soil compaction that might occur in pasture. Those are soil type, soil moisture content, and physical force applied to the soil.

Most farmers, ranchers, and gardeners mostly know that clay compacts much easier than does sand. The finer the soil the greater the likelihood of compaction. The coarser the soil the less likely it is to become compacted. While a lot of land managers are aware of this next point, sadly, many are not. That is soil organic matter content greatly modifies the resistance of all soil textures to compaction. The higher the organic matter content, the less likely it is to become compacted. The corollary principle is the greater the level of soil biology in the soil, the more quickly the soil will remediate any compaction that does occur.

The second factor of soil moisture content should be a guiding consideration in our daily grazing management choices. If we have a goal of grazing 365 days of the year, there is a very high probability that you will face many situations of needing to be on a pasture that is really too wet to be grazed that day. I will admit the probability of facing that situation is much greater in Missouri than it is in Idaho. Unless you’re on irrigated pasture where we must manage the ongoing interface between irrigation schedules and grazing plans.

Now, let’s consider the third factor which is physical force applied to the soil. In 1981 I attended my first International Grassland Congress as a freshly minted pasture researcher stationed at the University of Missouri-Forage Systems Research Center. The IGC was held at Lexington, Kentucky, just six months after I had completed grad school there. It was great to see and meet so many international experts in various aspects of pasture science. While there were hundreds of scientific papers and posters presented, there was one that really stood out in my memory. It is often on my mind even to this day.

I have thought about this particular study multiple times every year across the 43 years since I first heard Dr. Michael O’Sullivan from the Johnstown Castle research facility in County Wexford, Ireland, present this research. This was one of the very first studies that tracked cattle travel activity as it related to the grazing management regime.

This study compared the grazing behavior and daily travel distance of dairy heifers in either a set stock situation (continuous grazing) or in a rotational grazing situation. Yes, this study was done 45 years ago and it was a calendar based rotation regime, not an adaptive management situation. Had it been more adaptive grazing management, the results may have been even more profound.

The gist of the study was that while feed was abundant thru the flush growing season, the heifers in the continuous and rotational stocking situation traveled equivalent distances. That was approximately five to six miles daily. When growth rate slowed and relative feed availability declined on the set stock pastures, the heifers began to walk farther each day in their quest for a bite of feed. Average feed availability in the rotational paddocks was lower than it had been during the peak growing season but it remained adequate for the heifers needs.

How far did they walk? At the end of the study, the heifers in the set-stocked pasture were walking about 24 miles per day while the heifers in the rotational paddocks increased their daily travel only to about eight miles/day.

When we consider the physical force being applied to pasture soils to create compaction, that physical force is the number of hooves hitting the ground each day.

Think about your neighbor’s field where the cattle have been for the past five months and the scarcity of feed out there. Think about how far those cattle walk every day. Think about the thou- sands of hoofbeats striking the soil every day month after month. That is how compaction is created in a pasture.

Think about the herd I had on a small paddock at 80,000 lbs/acre liveweight when the afternoon thunderstorm dumped three inches of rain in 45 minutes. The field may have looked plowed, but the cattle were moved after the rain and they took their hoof impact away from this wet soil. The paddock was biologically healthy, so soil recovery began immediately.

Don’t worry if you pugged a field this day. Just move the herd and move on with your life. ■

Jim Gerrish is a practitioner, researcher, and educator in the realm of grazing management on pasture and range. You can learn more about implementation of and tools for Management-intensive Grazing at www.americangrazinglands.com. His books are available from the SGF Bookshelf