Dr. Jim Romo, a range ecologist at the University of Saskatchewan asks the question. “Why do we rest hay fields and not pastures?”
“We need to focus on the forage in the pasture and what happens before and after grazing,” says Romo. “Grasses are tough, if we just give them a rest.”
But really, how tough are they? That’s a question Romo and his graduate students have been trying to answer for a number of years now on the semi-arid prairie grasslands of southern Saskatchewan.
What they’ve found is each type of forage has its own rest requirements. Decreasers recover more slowly after grazing than increasers. That’s one reason why we frequently see invader plants in overgrazed pastures.
Sufficient leaf area must be left on the plants throughout the grazing season so they can photosynthesize and convert solar energy into plant food.
In this way, the rest period allows desirable forage plants to regain their competitive advantage in the field.
Romo’s research is conducted on southern rangeland pastures where very little growth is recorded after early to mid July. In very dry years, plants may need a complete growth cycle to recover.
On the semi-arid rangelands, Romo says grazed plants are properly rested when they produce as much as pastures that haven’t been grazed.
“Pastures grazed for relatively short periods of time followed by relatively long periods of rest allow the plants to recover their vigour and forage production faster than pastures grazed for a long time and give a short rest,” says Romo. Thus pastures that need to be grazed very early in the spring need a long time to recover before the next grazing.
In our work at Melfort we grazed fertilized crested wheat grass pastures first thing in the spring for about two weeks then kept the cattle off until early to mid October, after the growing season had ended.
Romo believes that grasses can tolerate grazing any time during the year provided they receive sufficient rest.
The length of that rest period is dictated by the time of the year, the soil type and climate. “In the southern Saskatchewan semi-arid prairie grasslands there is little risk of over-resting forage plants, but there is a big risk of overgrazing if plants do not have adequate time to regrow before grazing.” Plants must be allowed to go through at least one complete growth cycle between grazing events.
In the moist areas of the Aspen Parkland we did a lot of grazing research at Melfort on black soils and at the Pathlow Pasture Research Site on Grey wooded soils. We looked at a four-paddock grazing system where we rotated the cattle every 10 to 15 days to a different paddock depending upon pasture productivity. This gave us sufficient rest periods of about 30 days or more for the smooth brome, meadow brome, bluegrass and alfalfa plants to regrow before the next grazing session. It did depend upon having adequate rainfall.
At the Lacombe Research Centre in the moist soil zone of the Aspen Parkland, Dr Vern Baron has worked on regrowth of fertilized meadow bromegrass. He found that a meadow bromegrass tiller when grazed could sustain about four mature leaves. After it was grazed there could be about one original leaf (oldest and lowest) remaining on the tiller. It had to grow three more leaves to reach the total of four. Vern found that in midsummer it took about 11 days to fully grow out a leaf. So the total time for the tiller to provide three more leaves was 33 days or about a 30-day rest period.
“The tiller continues to develop new leaves,” says Baron, “but the oldest original leaf dies, so under good conditions there isn’t much to be gained with a rest period longer than 30 days.”
However, as temperatures cool towards fall, as soil dries out and days get shorter, it may take longer to grow out a full complement of leaves, because each leaf takes longer to complete. So, as we get closer to fall, the pasture rest period should become longer, and the plants may not get enough rest until the following year when growing conditions are again favourable.
Leaf development is critical to tiller and root development. The tillers and the roots that form from them are what makes a stand thicker or thinner. Thus that taking the time (or rest) to develop a full complement of leaves per tiller is important to maintaining tiller density and stand thickness. If it took 30 days to grow a total of four leaves on a meadow bromegrass tiller, grazing at less than 30 days thinned the stand. But waiting a bit longer than that seemed to sustain the stand density with more tillers.
This has a number of implications for pasture sustainability and longevity. Baron says, ‘‘excessively long rest periods result in a lot of dead litter and leaf material in the sward, causing forage quality to decrease. Depending on the location, species and time of year moisture appropriate rest periods in the Aspen Parkland may be from 30 to 60 days, with a good average of 45 days.”
Romo and his research team found similar plant response times for smooth brome and crested wheatgrass in their semi-arid trials.
The key thing to remember in any grazing operation regardless of where you live is to rotate when you graze a pasture or grazing area. Designate a different pasture each spring for the start of the grazing season and graze each pasture at a different time each year. You still need to wait until the three-leaf stage to start grazing. We have found that pastures or areas that were grazed at the same time each spring lost alfalfa plants after the third or fourth year. However, in one study at Melfort we found that the proportion of grass and legume didn’t change even after seven years with rotational grazing where the paddocks were grazed for 10 to 14 days followed by a 30-to 40-day recovery period.
Frequent clipping of plants in plots, as would occur under continuous grazing or rotational grazing with short rest periods, reduced the proportion of alfalfa in a brome-alfalfa sward more than when two or three clippings were taken each year.
Rest periods can also be used to rejuvenate pastures. In one study on the Pathlow pasture research site we looked at the value of not grazing an area until September each year after the plants had a chance to mature. This paddock had been continuously grazed since the mid 1960s and was so bare that we could hit golf balls off it. By grazing it only in September for two to three consecutive years we brought the grass back up to the a horse’s stirrup. It didn’t cost us anything out of pocket and it was a lot easier and cheaper that breaking and reseeding the land with bulldozers and heavy-duty seeding equipment. But you have to be willing to rest the land.
Jim Romo got really excited in his early years as a range professor when he read André Voisin’s book Grass Productivity. André was a producer in France in the early 1950s who believed in “rational grazing” as opposed to rotational or rationed grazing. He emphasized the importance of resting more than the grazing aspect of pasture management. A lot of our current grazing knowledge originated with André Voisin’s early work.
Next time you see cows grazing in the same pasture over and over for a long time consider what would think you if that was a haybine going around and around the field week after week.
For additional information visit www.Foragebeef.ca.