Annuals offer perennial advantange

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Fall is a critical season for the perennial pasture plant. It is during this time period that the perennial plant must store up carbohydrate reserves that will allow it to survive the winter period and initiate new growth next spring. The plant stores up carbohydrates through the process of photosynthesis, using the energy of the sun.

Photosynthesis

In order for photosynthesis to take place there has to be sufficient leaf area to capture sunlight. The bottom line message here is that pastures should not be overgrazed during the fall period, they need to be managed to keep adequate leaf area on the plant. The plant that can build up sufficient carbohydrate reserves has a large advantage over the plant that is overgrazed in the fall and goes into the winter with low carbohydrate reserves.

The challenge to grazing during the fall period is plant regrowth and recovery following a grazing pass. Day length is short and decreasing while temperatures are declining.

Leaf growth and regrowth is slowed down. In some years, moisture is also a limiting factor, contributing to even slower leaf growth and plant recovery.

On the other hand, during day light hours the rate of photosynthesis is not slowed down in healthy leaf tissue during the fall period.

In order to capitalize on fall photosynthesis and the resulting carbohydrate production and storage, it is advantageous to leave some extra leaf area on the plant. Think in terms of 4-5 inches of height for orchardgrass and at least 3-4 inches of height for tall fescue and bluegrass pastures.

Grazing alternatives

Fortunately there are some grazing alternatives that can be used during the fall of the year that can help to provide some relief for perennial pasture grazing. Those alternatives involve the use of annual crops.

Two common options are the use of cool season cover crops as alternative or supplemental forage, and grazing corn residue after corn grain harvest. To use either of these options does take some fore thought and planning to make sure the crop can be grazed, including fencing and water provisions.

When used appropriately, these annual crops can provide some additional grazing during the rest and re-charge period that perennial plants need during the fall period.

Grant funding

I had the opportunity through some grant funds provided by the Ohio Dairy Research Foundation to plant some forage cover crop plots on the Rupp Vue dairy farm in Wayne County that served as the host site of this year’s Manure Science Review event in August.

Those funds allowed me to also take yield and quality measurements on the plots. Plots were planted July 5, and I took yield and quality samples on August 22 and 23, 48-49 days after planting.

Samples were air dried and sent to a lab for wet chemistry quality analysis so results reflect quality losses and values associated with mechanically harvested stored forage rather than higher values associated with grazing.

Yields

Typically, to provide fall grazing, these annuals would be planted between the later part of July to about mid -August and then grazed 50-70 days after planting.

Dry matter yields and quality analysis would be similar to the results shown in the table. Dry matter yields could be higher if grazing was delayed to more than 50 days post planting and growing conditions were favorable. Another annual crop grazing option is corn residue or corn stalks after corn grain harvest. I attended the 2014 Farm Science Review and watched some of the field harvesting demonstrations.

Forage left behind

While the large combines and the speed of harvest was impressive, I was struck by the amount of forage left after the harvest pass in those corn fields and took some photos to document the quantity.

In many areas of the state environmental conditions have been very favorable for growth and there is/was a lot of tall corn out in the fields. This corn residue can meet the nutrient needs of ruminant livestock that are in early to mid-gestation.

The University of Nebraska has done a lot of research on the topic of grazing corn residue. A University of Nebraska study conducted over a 5 year period from 2004 to 2009 measured corn grain left in the field after harvest. An average of 1.0 bu/acre was available for livestock grazing.

Corn stalk grazing

A 2004 Nebraska beef report on corn stalk grazing included more information about the make-up of corn residue. Generally, stalks account for 49% of the residue dry matter, leaves 27%, husks 12% and cobs another 12% of the residue dry matter. Livestock typically consume any corn grain first. After the grain, plant leaves and husks are eaten and the last portions of residue eaten are cobs and stalks.

Strip grazing

Strip grazing across a corn field can even out the nutritional quality because livestock will be forced to consume both the higher and lower quality components of the residue within a given grazing period before the fence is moved to provide a new strip.

According to a South Dakota State University Extension publication entitled “Grazing Corn Stalks” a crude protein (CP) content of 8% and a total digestible nutrient (TDN) content of 70% can be expected early in the grazing period. Over time the nutritional content will decrease to 5% CP and 40% TDN.

A 2004 Nebraska beef report on corn stalk grazing listed the average TDN value at 54-55%. The University of Nebraska has a corn stalk grazing calculator spreadsheet available at: http://beef.unl.edu/learning/cornStalkGrazingCalc.shtml.

Calculator

I entered a 165 bushel/acre corn crop and an animal weight of 1,400 pounds According to the calculator, with a 50% harvest efficiency, one acre of this corn stalk residue could provide up to 60 grazing days for that 1400 lb. beef cow. Perennial pasture plants need to be carefully managed in the fall of the year to allow them to build up carbohydrate reserves. Grazing annual crops during this fall period can meet livestock nutritional needs and provide a benefit to perennial pastures.

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Rory Lewandowski is an Ohio State University Extension educator at Wayne County Extension.

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