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OSU Extension

College of Food, Agricultural, and Environmental Sciences

June 8, 2016 - 9:10pm -- lewandowski.11@...

Our recent period of above 80 degree days with no rainfall demonstrates how quickly we can go from saturated soils to looking forward to some rain.  For the livestock owner dependent upon pasture growth, our recent weather pattern of 80 degree plus days with no rainfall demonstrated how quickly growth rates of our cool season pasture grasses can be reduced.  Looking ahead to summer its likely we will see more of this kind of weather and even hotter and drier possibly.   There are management practices that can give the grass plant some advantages during hot, dry periods and help to keep cool season grass pastures productive during summer months.  Two big keys are leaf area or residue after a grazing pass and rest period between grazing passes.

The take half, leave half principle must be followed during the summer months.  The leaf area that remains after a grazing pass provides a photosynthetic base for plant regrowth, shades the soil to keep the soil temperature cooler, and it helps to reduce soil moisture loss.  In addition, research has shown that leaving half of the leaf area on the plant produces a minimal impact upon the plant root system, enabling that plant to continue to absorb nutrients and moisture and recover quicker.  Taking off 60% or more of the plant leaf area will cause a significant decrease in the plant root system that will slow down and impede the regrowth of the plant.  Do not cheat on this principle during hot, dry spells.  It is critical to maintain a 4 inch grass height to get the benefits mentioned. Maintaining this leaf residue provides the grass plant the best opportunity to take advantage of those spotty rain events that are common to hot, dry years, allowing regrow much sooner as compared to overgrazed pasture paddocks.

The second principle that must be adhered to is to provide a rest period that is sufficient to allow plants to grow back to a practical grazing height. Obviously the two principles work hand in hand.  The height at which grazing should begin is somewhere in the 8 to 10 inch range for grasses such as orchardgrass, fescue and festuloliums.  For bluegrass and perennial ryegrass pastures 6-8 inches may be used.    In practice this means that grazing rotations must slow down during hot, dry periods because grass growth and recovery is slower as compared to spring conditions.  When pastures are growing fast, rotate fast.  When pastures are growing slowly, rotate slowly.   Unfortunately it is easy to do the opposite and I have seen a number of pasture managers get caught in faster rotations during the summer with the end result that pastures become overgrazed leading to even slower recovery and less pasture production.

The only way to increase the number of days between grazing passes in a paddock and provide longer rest periods during the summer months is to have a sufficient number of pasture paddocks or pasture divisions.  The number of paddocks needed can be determined by this formula: Days of rest needed divided by days of grazing + 1.  For example, let’s say that in the spring of the year it takes 15 days for grass to regrow from 4 inches back to 8 to 10 inches in height.  If my livestock stay in each paddock for 5 days I need 15/5 =3+1 or 4 paddocks.  Now let’s say that as it gets warmer and drier it takes 35 days for that same pasture to regrow to an 8-10 inch height after being grazed down to 4 inches.  I now need 35/5= 7+1 or 8 paddocks to provide enough rest period.  If I have fewer paddocks I am either going to graze down the preceding paddock below 4 inches while waiting for the next paddock to regrow to the 8 to 10 inch height or I will enter the next paddock at a lower height and have less forage available.  Either way the end result is overgrazing, slower plant recovery, and less pasture production.  Generally between 8-10 pasture paddocks or divisions are needed to manage adequate rest periods during the summer.  I know of graziers that have 30 or more pasture paddocks.  I have never heard good pasture managers say they have too many paddocks.  

Summer weather with its hot temperatures and reduced rainfall result in reduced cool season pasture growth. While weather can’t be controlled, how the grass plant is managed during the summer can be controlled by the livestock owner.  Good pasture management can result in more productive pastures during the summer.