Any grazier knows that pasture management is as much of an art as it is a science. Skilled and seasoned graziers understand how important it is to keep a close eye on pastures as livestock are grazing, and often a drive-by evaluation of a pasture is not good enough to fully see what is going on out there - it requires us to get out of the truck and get our boots on the ground, walking the field to evaluate the current status. Often over-grazed pastures can appear to have more residue - or stubble - than they actually have when driving by or viewing from a vehicle window.
In the spring when conditions are favorable for cool-season perennial pasture growth (the most common type of pasture in Pennsylvania), it can seem simple to graze and get regrowth of forages after the animals have been rotated to a new paddock in a rotational grazing system. However, as the growing season progresses and the temperature becomes warmer and cool season forage growth slows, grazing management becomes even more critical if adequate pasture regrowth is desired.
Typically, a grazing residue height of 3-4" in cool season perennial grasses is recommended. During the peak growing season, graziers can easily graze more towards the 3" mark and still get adequate pasture regrowth if animals are removed from the paddock and pasture is allowed time to regrow - typically for 21-28 days. However, as the summer encroaches and temperatures rise, forage growth will slow and often times precipitation slows - and in some years, stops! It is important to remember that what is above the soil in terms of stubble height is reflected below the soil with root depth and mass. In other words, if the grass is grazed to a 1.5" stubble, there will likely only be 1.5" of root mass and depth below the soil surface. This isn't an adequate root system for forages to seek water availability during times of stress - high heat and water deficiency. Therefore, it is recommended that during those times of water deficit and high temperatures, a grazing residue height of 4-4.5" would be ideal, allowing the forage to have an adequate root system to seek out the nutrients necessary for regrowth during times of stress.
In the fall, as the seasons change and the temperature begins to once again cool, pasture regrowth of cool season perennials will jump once again. However, the plants are preparing to go dormant for the winter months. It is critical, once again, to not graze too close to the soil surface for that final grazing in the fall before winter. Research has shown that the higher the residue or stubble height in the fall, the sooner the pasture is able to be grazed in the spring and the more biomass is available the following grazing season.
So keep a grazing stick behind your truck seat and get out there and measure the pasture residue height. When it gets down to 3", make sure that livestock are being rotated to a pasture with at least 6-8" of forage growth and allow the previously grazed pasture adequate time to regrow.