How mob grazing impacts your soil

Drovers" December issue included a short profile of Missouri rancher Doug Peterson who was named a runner-up in our annual Profit Tips contest. The feature described Peterson's utilization of "high-density or mob grazing, which stocks cattle at a high rate for a short period of time, then removes the cattle for a lengthy rest and regrowth period. Such intensive grazing forces cattle to eat the forage available to them and provides significant fertilizer to the paddock."

Shortly after the story was published a Texas rancher wrote with some questions: "I am a bit confused about how this ‘provides significant fertilizer" in comparison to other grazing systems." The Texas rancher asked for more information about mob grazing and its impact on soil nutrient management of the pasture.

Since Peterson is also an NRCS state grassland conservationist in Missouri, he provided further explanation of the advantages of high-density or mob grazing.

"It is correct that grazing does not add fertility to the field. However, using a very intensive grazing system does pull up minerals that are not available to plants managed in a more continuously grazed manner, and we can significantly influence where the nutrients in the livestock manure are deposited," Peterson said.

"Research at the University of Missouri's Forage Systems Research Center, Linneus, Mo., actually counted the number and location of manure piles under different types of management.

"The study showed it would take approximately 27 years to get one pile of manure distributed to every square yard of the pasture. Obviously they extrapolated their data to get that figure. In a continuous-grazing system, livestock do the majority of their grazing and loafing near shade or water, so most of the manure gets dumped near those two locations.

"Even if the cattle go to other parts of the field to graze, they will actually move soil nutrients around in a pasture by dumping them where they spend the majority of their time, near water and shade. By utilizing a grazing system and controlling where the livestock spend their time we can actually control where the manure is deposited. The study shows that in a grazing system that moves cattle every two days you should expect a manure pile on every square yard once every two years. That is a significant change from 27 years.

"In a really intensive system like ours where livestock move daily, or even several times a day, I would assume we are getting even better distribution than that. Here is the actual data with two lines that I added on the bottom.

"In Missouri we take soil samples to a depth of 6 to 8 inches. Originally it was done because that was the ‘plow layer" for annual crops. It is still a valid depth because most cool-season-grass pastures are managed in a continuous-grazing system, and the plants only have root systems a few inches deep. There isn't much need in going deeper because, for the most part, the plants just won't pull significant amounts much deeper than 6 to12 inches. In areas that have deeper-rooted warm-season grasses, that will change some. But the root mass of almost all plants is a reflection of their above-ground biomass. Short tops mean short roots.

"In a really well-managed grazing system with fairly long rest periods, we can get cool-season-plant roots that are several feet deep. In our grazing systems we try and allow the plants to reach as mature a stage as possible. This allows them to have a very deep root system. Here is some data from a NRCS typical pedon for an Armstrong soil. It is the third most common soil in Missouri. Yes, there is fertility on the surface because that is where the fertilizer has been added, but it shows significant amounts of minerals below 8 inches.

"If we don't manage our plants to have roots deep enough to go down and get those minerals we are giving up a huge financial opportunity for a wealth of minerals. The only way we can get deep-rooted plants is to very intensively manage them in a grazing system.

"Nitrogen is also a consideration, as it is the primary item that is removed from the soil by marketed livestock. We maintain a large legume component in our pastures. The only way we can maintain legumes is with our intensive-grazing system. We seldom add any legumes to the pastures. This legume component can pull 100 to 200+ pounds of nitrogen from the atmosphere every year and add it back to our soil. Other minerals are removed by livestock that are sold off of the farm, but only in very small amounts. Over 90 percent of the P, K and Mg taken in by a grazing animal comes out the back end. By offering free-choice minerals to the livestock we are offsetting most of these losses.

"To summarize, with high-density grazing we are not adding minerals to the system in the traditional sense that most people think of with a fertilizer cart but I do think that we are utilizing sources of fertility that most people are losing or just can't get to with more conventional continuous-grazing systems," Peterson said.