André Voisin is arguably the first scientist who began documenting how animals, pastures, and soils develop together, not as three separate entities. Through his book Grass Productivity, it became known that the movement of animals across pastures determines the plant species that survive and the soil structure that supports them. As Voisin explained, the difference between rotational grazing and his rational grazing was the annual cost of pasture renewal.
If severely grazed, a grass plant uses energy stored in its roots to replace the green leaf. Once green leaf emerges the plant can photosynthesise its energy for tissue renewal. If animals are left in a paddock, they will graze the lush regrowth of severely grazed plants. This occurs because animals prefer to graze the freshest and leafiest parts of any species. Therefore, long grazing periods lead to overgrazing no matter how big the paddock and how small the mob.
What Voisin also pointed out is that returning animals to a paddock when the plants have not recovered from severe grazing is also a recipe for disaster. When done several times in a season, this practice strips the root system of the carbohydrates needed to grow the initial green leaf. Therefore, the plant’s ability to buffer drought, wet, or cold is diminished. As a result, the plant grows less grass, the farm experiences a shorter grazing season, and eventually the paddock burns out.
The point can be illustrated with the diagram here. Assume a farmer chooses to operate a 15 day rotation, a situation that plant B can handle. However, pastures are never grazed evenly so that both plants A and B will be in a paddock. Returning on day 15 will suit plant B as its root system will have recovered fully. However, plant A being more tender will be regrazed before its root system recovers. Done repeatedly, this practice eventually kills the plant A and the pasture will need resowing.
If plant A is a ryegrass and plant B meadow grass, guess which species will eventually dominate the paddock. This is why the practice of set stocking early in the spring encourages clover growth often at the expense of other species like ryegrass and cocksfoot. Set stocking later in the spring once ryegrass has recovered from winter grazing would strengthen its presence in the sward. In drought prone areas, such a practice would ensure less bare earth in paddocks over summer. Clover shrivels up under drought stress, exposing more soil to the sun, reducing soil moisture retention, and increasing erosion once the rains return.
Monitoring pasture species is a useful skill to determine whether a pasture needs to be grazed differently. Combining a review of pastures species with your grazing activities will give some idea of what changes should happen to reverse the situation. This skill is simple to learn and understand, but the habit is a little harder to implement.
Strategies to reverse a situation might include; daily shifts using electric fence, the use of attractants like molasses or salt, or changing lambing/calving dates. These practices an only be done successfully when families know the type of pastures they want and have a good understanding of how grazing behaviour influences pasture species and land function in that direction.
The saying “you get the pastures you graze for” has meaning. The timing of grazing determines what species remain in a pasture. In particular, the recovery of desired species to replenish their root reserves is essential for their survival. This requires good observation and analysis skills about the grazing activities undertaken on the farm.