The debate around optimally managing rangeland has raged on after analysis of many grazing experiments failed to show any advantages in rotational grazing over continuous grazing. While rotational grazing was once considered a scientifically superior approach, further investigation has shown that it falls short of scientific and ecological correctness.
Holistic planned grazing (HPG), although not strictly rotational grazing, also relies on the regular movement of livestock across the range according to a specific grazing plan. But HPG has the same key conceptual flaws found in rotational grazing. Similarly to rotational grazing, HPG attempts to minimise selective overgrazing of palatable grasses and undergrazing of unpalatable grasses, while affording grasses a long recovery period after grazing. These are both important goals, but achieving them, especially without negatively affecting animal production, requires a fundamentally different approach to grazing management.
HPG also incorporates simulating the impact of vast herds of wild herbivores that once roamed African grasslands and savannas. This impact included the positive effects of continually shifting the grazing pressure over vast areas of the landscape. In addition to non-selective defoliation of grass tufts, the resultant trampling broke up crusted soil and buried seed, while dung and urine fertilised and returned nutrients to the soil.
These scientifically verified factors are certainly important in increasing the nutrient cycling rate and grassland productivity, while facilitating establishment of new seedlings. HPG proposed that a herd moved into an area, grazed down all the grass and then moved on, leaving the grazed grasses for long periods to recover.
In reality, herbivore use of landscapes is far removed to what is proposed here. As will be shown shortly, any grazing management strategy based on this erroneous concept of herbivore grazing ecology is conceptually flawed and is likely to yield suboptimal results. Unfortunately, many farmers are lured into introducing HPG because the concept sounds so appealing.
However, without sufficient and applicable knowledge of grazing and herbivore ecology, they cannot adequately assess the validity of the ideas and concepts which holistic management workshops promote. There are four key concepts that form the pillars of healthy and productive grazing ecosystems and herbivore populations. Both rotational grazing and HPG fall short of ecological correctness in this regard, and are therefore suboptimal strategies for managing most rangelands.
Carrying capacity is strongly driven by grass productivity. There is a positive linear relationship between grass production (kg/ha) in various national parks across Africa and the large herbivore biomass these parks support. This is fairly obvious, but the implication is that carrying capacity is not a constant and can be improved or degraded by increasing or decreasing grass productivity.
Clipping and grazing studies have demonstrated that current growing season grass productivity is strongly driven by the grazing pressure on the grass during the previous growing season (Figure 1). Rotational grazing violates this principle by grazing all the camps on a farm in each growing season, thereby reducing the optimal recovery period of the grass. This may reduce the abundance of palatable perennial grasses and therefore the productivity of the grassland in that camp.
Note how clipping grasses in the first year did not reduce productivity because the grasses had rested the previous year. Courtesy of Ecological Society of America
Defoliation during grazing leads to a loss of key growth-limiting nutrients such as nitrogen, which the grass plant must then recover to avoid declining productivity. Most nutrients become available for plant uptake during the early wet season – the peak of the mineralisation process. Mineralisation is the microbial conversion of minerals stored in an organic form in plant residue to a mineral form in the soil, which then again becomes available for plant uptake.
Remobilising growth-limiting nutrients stored in root biomass to produce new leaves enables grass regrowth after grazing. As a result, roots start to reduce aerial growth and instead produce new leaves. However, root biomass mainly develops during the late wet season. Grasses therefore need a full year’s recovery to enable maximum uptake of growth-limiting nutrients in the early wet season, as well as maximum storage of these nutrients as root biomass in the late wet season. Such grasses will be extremely productive during the next growing period.
Optimal cattle production is achieved by keeping grass height/maturity at an optimum to maximise quality (energy and protein content and digestibility) and intake rate. Rotational grazing disregards this principle by providing for long recovery periods between grazing events, thereby allowing the grass to mature beyond the optimal grazing stage.
Studies at Dohne Research Station in the Eastern Cape show that allowing grassland to mature before grazing can reduce the weight gain of sheep by up to a 60%.
Poor nutrition has other negative effects on animal production, such as a reduced birth rate and calf size at birth, while increasing the age of first conception. This explains why many HPG farmers have difficulty achieving high conception and birth rates among their cattle, increasing the need for lick supplementation.
Rotational grazing and HPG strategies, which allow long recovery periods between grazing, have the following negative effects on farm productivity: reduced animal production, increased need for lick supplementation with associated costs, reduced grass production due to aging leaves, and increased shading by dead leaf material. These factors reduce the productivity and profitability of the farm.
Optimal grazing management should therefore aim to sustain sufficient grazing intensity during the growing season to maintain the grass sward at an optimal height and state of maturity for maximum animal production.
Movement between a shorter, but higher quality wet season range and a taller, but lower quality dry season range results in maximum stability and productivity in a herbivore (cattle) population. All known wild herbivore and transhumance migrations in Africa follow this grazing pattern, indicating its obvious biological advantage. If the long-term viability and success of a herbivore population depends on following such a grazing pattern, we need to take note and learn.
The reason is that the high quality, wet season range maximises energy and protein intake for growth and reproduction. The taller dry season range provides a reliable forage reserve during the resource-limited dry season, especially during drought, and minimises weight loss and mortality. Concepts 3 and 4 make it clear that wild herbivores seek to graze grassland of optimal height and maturity to maximise their energy and protein intake.
They will rarely naturally follow a grazing pattern promoted by rotational grazing, especially under HPG, where grassland is rested for months before cattle are allowed to re-graze it. In reality, studies of wild herbivore grazing ecology show that the animals favour highly digestible, immature grassland from which the older low quality plant material has been removed by fire or grazing. Thus, they return to grazed areas to regraze the high quality regrowth – a concept known as grazing facilitation.
It is claimed that HPG attempts to simulate natural grazing patterns. According to this system, large herds of cattle are moved into veld that has been grown out after a long rest period and leaving them there for a short period. However, this means they do not benefit from the high quality regrowth after grazing.
Many HPG farmers have built their grazing strategies on false concepts with negative consequences for cattle production and profitability. The same can be said for most rotational grazing strategies. Unfortunately, most farmers, and even rangeland scientists, are unable to evaluate the validity of ideas promoted in HPG or rotational grazing, as they lack the specialised technical knowledge of herbivore grazing ecology.
The way forward
The way forward is to incorporate these four key concepts into a new optimal rangeland management strategy that, unlike HPG and rotational grazing, does not violate these key concepts. Such a strategy must provide year-long recovery periods for perennial grasses to achieve optimal range condition and productivity. It must also be ensured that grazed portions of the farm are maintained in an immature, high-quality state during the wet season for maximum cattle production.
To achieve this, the farm should be divided into two halves, and each half switched between the two conditions (rested vs grazed) in alternative years. All the cattle on the farm should be concentrated on the grazed half for a full year at sufficiently sustained grazing pressure to maintain the grassland in an immature, rapidly-growing and high quality state. At the same time, a full year should be allowed for recovery of grasses on the ungrazed half. As grazing greatly reduces seed production, resting half the farm for a full year also allows grasses to maximise seed production for new seedling establishment.
After a year-long recovery period, grasses on the newly grazed half of the farm will have developed a large forage reserve to support the cattle over the dry season and are so productive that they easily support the entire farm’s cattle population during the wet season. The farmer then has built-in fodder flow insurance and is less dependent on supplementary feeding, thereby maximising profit.
Being less reliant on a complex system of internal fencing that eats up money further maximises profit. In addition, the need to move cattle between small camps is greatly reduced. This lessens management and labour requirements and interference with the cattle’s optimal foraging ecology.
It is better to allow cattle to range over a larger area and select grazing spatially according to their specific needs (adaptive foraging), than forcing them to be where they don’t want to be and continually moving them through restricted camps. The latter greatly restricts optimal resource selection and increases the animals’ stress.
Holistically speaking, the split ranch/farm strategy is ecologically and economically optimal, and the most favourable for the farmer and cattle’s quality of life.
The configuration of the grazed and rested portions will vary according to a farmer’s needs. It can range from only two camps (a grazed and rested camp, alternated between two years, Figure 2A), to more complex designs in which the farm is divided into several cells, each consisting of grazed and rested camps, with each cell containing a single herd to separate breeding herds, weaner herds, and bull herds.
The split farm grazing strategy can be run as a simple system in which the farm is simply split into two halves (A), or a multi-cell approach (B) where each cell is split into two halves with a herd contained and managed within that cell, as a farm within a farm.
Each cell then effectively becomes its own micro-farm (Figure 2B). However, it is best to keep the design as simple as possible to reduce fencing and management costs and allow for larger camps that can facilitate optimal adaptive foraging.
This rangeland management strategy is increasingly used with great success by farmers in South Africa, Namibia and Botswana. Rotational grazing and HPG fall short of the four concepts described, whereas this split ranch grazing strategy is conceptually robust, supported by wildlife grazing strategies and is less complex and expensive to implement and manage.
Email Dr Richard Fynn at [email protected].