By Dan Undersander
With the drought last year and short forage supplies we need to maximize the production of pastures to reduce the need for harvested and stored forage.
Don't overgraze
Some rest periods for the grass pasture over summer over summer will dramatically increase forage yield. A basic rule of grass growth is that growth takes priority over storage for carbohydrates. If grazing animals remove most of the available leaf area every few days, the plant allocates nearly all growth energy to new leaf growth, the root system diminishes, and less energy is stored. Frequent leaf removal without adequate time for the plant to restore its vigor is the physiological basis of overgrazing which results in yield far below their potential, maintaining only a low stand density and poor vigor.
Most grasses store some energy for regrowth in stem bases so grasses need to be grazed or mowed higher (3 to 4 inches) than legumes (table1). Some grasses are slow to recover because they only produce buds for regrowth after they have been cut or grazed (e.g. bromegrass and timothy). Other species produce buds sooner in the growth cycle and therefore recover faster for haying or grazing (e.g. orchardgrass, tall fescue).
Some grasses have basal leaves that remain after mowing or grazing which help the grass grow back faster. From table 1 we see that bluegrass and ryegrass are this way. Orchardgrass, reed canarygrass, tall fescue and smooth bromegrass will have some leaf area remaining if cut or grazed at 4 inches or higher but not if cut shorter.
Thus two-week rest periods at least twice during the year will greatly increase forage production.
Lastly it is important to note that grasses need nitrogen fertilization continuously throughout the season. Grass takes up on available nitrogen on a growth cycle and leaves little for the next. Nitrogen deficiency is quite visible in pastures where the tall green ring around a manure pile indicates how tall the rest of the pasture could be if it had received the same nitrogen.
A basic rule of grass growth is that each growth cycle takes up whatever nitrogen is available. Thus first growth in the spring takes up any residual nitrogen that was in the soil and all fertilizer nitrogen applied. Thus, no matter whether we apply 50 or 100 pounds of nitrogen per acre to first cutting, there will be little residual for the next growth. In practice we can often get two cycles of grazing from an application of nitrogen but then are deficient for the next growth cycles. This is why grass often grows taller around manure piles in late summer – it is getting additional nitrogen.
The study in table 2 shows that where multiple nitrogen applications of 50 units each were made on May 1 and June 15 (100 units total) and on May 1, June 15 and August 1 (150 units total). Results presented here are averaged over 2 years.
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Table 2 shows total yield for untreated plots and yield increases for each of the nitrogen application strategies. The greatest yield increases were recorded in the smooth bromegrass and orchardgrass pastures. Multiple nitrogen applications provided the greatest yield increases, however the June 15 applications contributed very little to this increase. For example, the May 1 to June 15 treatment increase was similar to the May 1 single application, likewise the May 1, June 15, Aug. 1 treatment increase was not much different than the sum of the May 1 and Aug. 1 single applications. The lack of summer response is likely due to the overriding effect of dry growing conditions.
Thus while pastures green up in the fall they produce little forage unless fertilized. An application of nitrogen around Aug. 1 will increase fall growth by half to one ton of forage per acre.
Undersander is a University of Wisconsin-Madison Extension forage agronomist.
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Table 2. Yield increases from nitrogen application |
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Kentucky bluegrass |
Smooth Bromegrass |
Orchardgrass |
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Control Yield (lbs DM/acre) |
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4365 |
5293 |
4654 |
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Yield Increase (lbs DM/acre) |
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May 1 |
246 |
1326 |
1052 |
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June 15 |
14 |
456 |
516 |
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August 1 |
232 |
1002 |
729 |
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5/1 + 6/15 |
710 |
1054 |
1062 |
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5/1 + 6/15 + 8/1 |
885 |
2019 |
1284 |
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Table 1. Characteristics that affect harvest management of grasses |
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Type of regrowth |
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Tall fescue |
No stem |
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Orchardgrass |
No stem |
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Kentucky bluegrass |
No stem |
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Reed canarygrass |
Stem |
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Smooth bromegrass |
Stem |
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Timothy |
Stem and seed heads |
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Ryegrass |
Stem and seed heads |
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Carbohydrate storage site |
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Orchardgrass |
Stem Base |
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Tall Fescue |
Stem Base |
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Reed Canarygrass |
Stem Base |
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Ryegrass |
Stem Base |
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Timothy |
Corm |
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Smooth bromegrass |
Roots & Rhizomes |
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Tall Fescue |
Roots & Rhizomes |
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Reed Canarygrass |
Roots & Rhizomes |
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Kentucky bluegrass |
Roots & Rhizomes |
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Basal leaves |
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Ryegrass |
Yes |
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Kentucky bluegrass |
Yes |
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Orchardgrass |
Management dependent |
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Reed canarygrass |
Management dependent |
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Tall fescue |
Management dependent |
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Smooth bromegrass |
Management dependent |
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Timothy |
No |