Plants are not all thinking the same in terms of their end goal with pasture rest. However, the one thing they all have in common is the need to bring in plenty of carbon. What animals chose to eat and when, has to be considered when implementing resting programs.
While perennial plants initially concentrate on growing new leaves after rain, they are very focused on using incoming carbon to replenish their energy reserves and build an extensive root system. This ensures they are always in the position to produce leaves above ground for carbon collection. For annuals, the goal is to bring in plenty of carbon quickly to complete their growth cycle and produce enough seed for the next generation. Naturally, perennials need to produce seed over time, but it is a lower priority. The annuals are opportunists who take advantage of short term favourable conditions, while perennials are in for the long haul.
Now an important point in relation to short term removal of animals resting all plants: not all of the necessary carbon will actually come in during the rest period, but it will come in as a result of animals being removed for about four weeks.
THE MECHANICS BEHIND ANIMAL & PASTURE INTERACTION
The crux of what follows is that unless animals choose to consume it, a specific plant is being rested even if animals are on the pasture. SO, understanding how animals select their diet is critical to resting pastures successfully.
The table below explaining plant characteristics gives an insight into animal plant interaction over time. Most producers will not have the third group, the perennial edible shrubs like old man saltbush in their pastures, but they have to be included in this discussion for those who have this third tier of carbon collection.
The plant groups are listed in order of decreasing palatability. In the same order, their growth cycle gets slower. The annuals are the most palatable and grow the fastest. At the other extreme, the perennial edible shrubs grow the slowest and are the least palatable.
Animals select to maximise their protein/nitrogen intake, i.e. they select plants or plant parts that have the lowest carbon:nitrogen ratio. They are going to select annuals first, then perennial grasses and finally perennial edible shrubs. Natural systems have evolved to ensure shrub protein is saved for dry times.
WHAT HAPPENS WITH A SINGLE FALL OF RAIN
If good rain is a single fall, then the annuals will usually not establish during the four weeks following, and the most palatable feed on the return of the livestock will be the perennial grasses.
Four weeks’ rest, assuming they are resilient, will see perennial grasses reach the threshold of critical mass required, then they can easily stay in front of animal consumption and continue to build bulk.
IF RAIN GERMINATES ANNUALS
In regard to timing, pasture rest starts when plants start to grow, not the day after rain. This little extra time means the annuals, the first choice of animals, are growing quickly by the time the animals return.
Animals set out to consume a given volume of plants, not a certain number of plants. The more the most palatable annuals have bulked up, the more they remove grazing pressure off each other when domestic animals are returned to the pastures.
Also, it has to be remembered that livestock do not consume all the plants the first day they are re-introduced to pastures. Therefore, even for the most palatable plants, the actual rest time will always be longer than the exclusion time of animals. This gives the annuals a chance to set some seed.
Because the animals seek out the annuals on their return, this takes a lot of grazing pressure off the perennials and gives them more time to complete their cycle.
When animals return, if either the more palatable annuals or perennial grasses are available, then the least palatable, the perennial edible shrubs like saltbush get extended rest. They are free to grow for a considerable time, even although the livestock are on the pastures. They need this extended time to leaf up as they are slow growers.
WHAT HAPPENS IF PASTURES ARE NOT RESTED AFTER RAIN
At opening rains, perennial grasses respond the quickest, and their succulent shoots are readily eaten by stock, as they are available before the germinating annuals.
When animals are not removed after rain, the landscape suffers on two counts. The animals can over consume the fresh new shoots which the perennial grasses produce by drawing on energy reserves. We have all witnessed animals chase green pick. If these new shoots keep getting completely removed, then the perennial grasses have to keep calling on energy reserves to keep producing them. As well, animals pull the more favoured annuals out of the ground before they have time to develop secure roots. Oats is an annual plant, and croppers never move livestock onto these crops as soon as they germinate. They let the crop develop roots and build bulk before it is used.
Implementing tactical rest after rain enhances the chances of germinating perennial grasses becoming established. This is because the animals will select the annuals in preference to the perennial seedlings.
A PRACTICAL EXAMPLE
In January 1995, when there was perfect germinating rain, I succeeded in re-establishing perennial grasses from seed by removing the stock for only 4 weeks. On their return, the animals, in this case sheep, focused on the annuals and even ignored the perennial seedlings around the watering points. Only mature animals were returned as they had perfected their selection process and were less likely to select the perennial seedlings over the annuals. At the end of the exercise, the annuals dropped plenty of seed.
ENCOURAGING ANIMAL SELECTION
When plants have had sufficient rest to protect their future, allowing animals to select the most productive plants available is not an issue. Animals need to be allowed to perform to their genetic potential. Exposing ruminant animals (sheep & cattle) to the highest quality diet possible, increases their growth rate and reduces methane produced per kg of production. Because about 4 weeks rest spells all plant groups (the first two groups for most producers), the animals can start with the most palatable and consume the plants in order of preference as the season deteriorates. Having leftover bulk of some of the inferior grasses as the season deteriorates, then becomes low quality gut fill to go with supplements, or the protein supplied by edible shrubs.
The only way to spell a particular plant while animals are on the pasture, is to have more palatable plants available for the animals to choose.
If a plant is on the menu of animals, then it is protected by how many mates it has and how big they are.
If all the plants in a pasture have limited growth, then animals can maintain ongoing pressure on the entire pasture.
The required rest period after rain is determined by pasture resilience, because the level of resilience determines pasture response to rain. Also, the warmer it is, the faster pastures grow.
In a perfect world, pastures would be rested after every rain event. In a practical sense, they need to be rested enough to maintain resilience.