Managing Pastures during the Late-Growing Season

GLEN AIKEN 

Our cool-season grass pastures are in the second half of the growing season, and it is time to think about preparing them for cold weather and spring green-up.Yes, I said spring green-up, because management inputs that prepare your pasture forages’ root systems to survive freezing ground temperatures and provide maximum storage of nutrients can promote early spring growth. In other words, your pastures get a good start in the next growing season with good grazing management and fertilization in the fall.    

Pastures are generally not as productive in the fall as during the spring season, so you may wonder why full attention is not spent on promoting and utilizing the spring growth.  Maximizing and utilizing spring growth should be a priority, but fertilizer application and sound grazing management decisions in the late-growing season can promote winter survival, which can carry-over into an early and strong spring growth. 

Why would we want to fertilize in the late summer or early fall?  The answer is: why not?  An application of 50 to 70 pounds of nitrogen from early August to middle September can generate growth of fall pasture.  Much of this growth is due to increases in tillers/shoots that increases ground cover and thickens grass stands.   An application of nitrogen in early to mid-August is routinely recommended for stockpiling tall fescue to maximize pasture growth for winter grazing that will save dollars spent on hay and feed. 

A fall application of nitrogen will also increase storage of nitrogen in the root systems, needed for maintenance during the winter months, and growth as air and soil temperatures rise in the early spring.  Although a late application of nitrogen in October may not generate a reliable amount of forage growth, it can conserve the nitrogen stored in the roots to generate stronger and more productive grass stands in the spring.   

Phosphate and potash are ordinarily applied in the spring, but the fall is also a good time to spread these nutrients.  If soil tests state that phosphate has dropped below 60 pounds per acre and potassium below 120 pounds per acre then it is wise to apply these nutrients prior to the onset of winter.  Both of these nutrients have critical functions in growth and maintenance of grass and legume root systems.  Fall is also a good time to spread lime if needed to increase soil pH.             
     
It does not make much sense to fertilize during a dry summer, but there will likely be some showers in the fall before freezing temperatures.  Grass plants that are stressed from hot and dry summer weather have less chance to recover with fall rains if fertility is low. Consequently, plant losses can be high and pastures will exhibit deterioration in the spring following a dry summer with overgrazing, and low fertility in the fall.    

Best grazing management practices in the late summer and fall will also improve winter survival and spring growth.  Pastures should be rotationally stocked such that cool-season grasses are grazed to a 3- to 4-inch height and rested to obtain above a 6-inch pasture height before grazing again.  Perennial grasses and legumes during the fall are primarily growing new tillers and leaves to increase their capacity to produce soluble carbohydrates through photosynthesis.  During the fall, a substantial amount of these carbohydrates are routed to the root systems for storage and used as an energy source during the winter and spring green-up.  You can think of the fall as a time when perennial grasses and legumes are trying to prepare themselves for freezing temperatures. 

The fall growth must be grazed, but enough green residual should be maintained for recovery growth and replenishment of stored carbohydrates in the root systems.  If there is not enough leaf material to generate enough carbohydrate for new growth, the plants will draw the needed carbohydrate from their root systems.

Make sure to reduce thatch in pastures that are going to be frost planted with clovers.  In late November or December, graze all pastures to a 3- to 4-inch height.  However, successful frost planting of clovers is doubtful if there is excessive amounts of mowed material on the ground.   Mowing might be needed if there are ungrazed weeds or summer grasses, such as fox tail.  You could be inclined to graze or mow close to the soil surface, but why give spring weeds room to emerge and have some competitive advantage with the grass and emerging clover?  

A final note in regards to stockpiled ‘Kentucky 31’ tall fescue: Ergot alkaloids are oftentimes higher in the fall than in the spring.  Fall growth of tall fescue that is fertilized in the late summer has the greatest potential to be very toxic.  It is advisable that fall growth of tall fescue not be grazed until after a hard freeze—less than 27 degrees Fahrenheit—that inactivates fescue growth.
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Next month, I will discuss the ergot alkaloid toxicity of Kentucky 31 tall fescue in the fall.