Google Earth, Rotational Grazing and Mineralization

Or, What You See from Space (and What You Don’t)

Part 1 of 2

A key to the success of Farmland LP is having great livestock managers to make the most out of our high quality pasture.  In Oregon, Mac Stewart of Vitality Farms runs sheep on over 900 acres of Farmland LP property.  And now you can see his work from space.

New Google Earth Imagery

Google Earth recently updated the satellite imagery covering our properties in Oregon.  The resolution is so good that in the image below you can see individual sheep grazing in a paddock.

Our western property boundary is shown with a blue line.  A wheel line (for irrigation) is adjacent to the property line.  Off-white oval specs are the sheep.  They are in a paddock made by temporary electric fencing that is about 160 ft from north to south and 820 ft from west to east, about 3 acres. To the south of the current paddock is the previous paddock.  It is less green because much of the vegetation was eaten by the flock a couple of days before.  The dark green paddock to the north was set up just prior to when this image was captured.  The sheep will be moved there later in the day. Shepherd Mac Stewart changes the length of stay for the sheep based upon the size of the flock, the pasture quality and growth rate, the weather, and many more factors—all to encourage the pasture and lambs to grow steadily.  In two separate posts, I’ll explain a number of key concepts in pasture and flock management (Part 1) and how good management leads to an increase in the quality and value of the soil (Part 2).

Pasture Diversity and Productivity

Some people think pasture is just grass on poor quality ground, but great farmland can also be extraordinary pasture in terms of productivity and environmental and economic yields.  There is an entire science behind it. As a simple example, our custom blended pasture mixes include a lot of plant diversity with the goal of evening out the productivity of the stand over the year, since the sheep need food for 365 days.  For our Oregon properties and their associated climate, the grasses, such as tall fescue, orchard grass and perennial rye grass, do best in the cool months.  To take advantage of growth over the summer we also sow forbs that like it warm, such as chicory and plantain.  Clover diversity, including red, white and alsike, also extends the season of legume productivity.  The chart below (from this University of Arkansas web site) shows how the growth of different forage classes is distributed during the year.  The growth curves in Oregon are not exactly the same as what is shown below, but the concept applies everywhere—add diversity to enhance and spread-out the productivity. The picture below shows the same location as the Google Earth image above, except viewed from the ground (you can see the lone Oregon Ash tree in the background).  It was taken August 15th, about a month after the Google Earth image above (July 9th), and you can see the plant diversity in our pasture and that it is ready to graze again.  Healthy pasture makes great lamb.

Payse Smith, a student at Oregon State University, is shown above.  He is taking standardized samples of the field to determine the standing biomass.  We use this information to study the growth and recovery rates of our pasture, which ultimately determines the optimal number of animals for the field.  I’ll explain how this works with some illustrative numbers to keep it simple.

Rotational Grazing by the Numbers

A flock of sheep eats about 5% of its body mass in dry matter each day.  If we have 1000 sheep with an average weight of 90 lbs, the total biomass of sheep in the flock is 90,000 lbs.  Multiply 90,000 lbs of sheep by 5% to get 4500 lbs of dry matter per day required for the flock.  Now we don’t want the sheep to eat ALL the vegetation in the paddock, and a good rule of thumb is to only consume half the total biomass so that the pasture has leaves available for a fast recovery.  I explained this in a post from two years ago, and the relevant portion is repeated here: Pasture experts talk about the S-curve.  This refers to changes in the rate of growth of the stand of plants.  When plants are very small, they put on only a small amount of biomass per time.  But at a certain size, the amount they add each day increases rapidly.  Of course any exponential rate of growth must end, and so growth slows and halts as the plants reach maturity.  S-curves are common in all biological growth systems.  What good pasture management does is keep animals eating much of the pasture before it reaches the mature, no growth stage, but not so much that the pasture has a very long recovery time because the plants have been eaten back to the slow-growth portion of the S-curve.

Back to our example of the flock of 1000 sheep…If the flock needs to eat 4500 lbs of dry matter in a day we need a paddock with around twice this amount, or 9000 lbs.  Since each acre has a standing dry biomass of about 3000 lbs when it’s at the top of Stage 2 in the S-curve, a 3 acre paddock will comfortably feed those 1000 sheep for a day. This is good forage management and gives us the ability to grow high quality lambs as quickly as possible during the main months of productivity, which here in Oregon is April through October.  But it also does something else very important to the soil.  As the plants grow, are eaten just right, and regrow again—a cycle that repeats up to seven times per year—the soil organic matter (SOM) increases.  Instead of buying in tons of compost per acre, at a cost of many hundreds of dollars, our pasture produces tons of soil organic matter per acre.  SOM does many things to improve soil quality, including increasing water holding capacity and improving soil tilth, and, as I’ll explain in Part 2 of this post, it stores nutrients that become available to plant roots through a transformation termed mineralization.  So even though you can’t see it from space, what is happening below ground may be more beautiful than what is happening above.