An ongoing debate: Planned or continuous grazing? (3/3)

All this week on Table Talk we will look at the theme of Grazing Management


In our final post for the week, we turn to research and trial results to try and make more sense of the debate surrounding grazing management. As noted by Terry McCosker,

A sure-fire way to spice up a barbecue debate is to state your opinion on ‘cell grazing’. A lot of money has been invested in research to determine which grazing system is best. Unfortunately, the research is flawed with regards to giving us good, commercial information that is relevant to what graziers actually do.

Kate Sherren and Carlisle Kent state that the debate between rotational and continuous grazing has been ongoing since the 1950s and the evidence is perennially mixed. It remains the most persistent debate in grazing management. They state:

Science is divided on the utility of such practices: experimental scientists see no benefits from the constituent practices in controlled experiments, particularly not the scale of production increases promised by Savory, while many management-oriented agricultural, ecological and social scientists report benefits at the farm scale

Today, looking at both sides, we bring together research, trials and meta-analyses to help shed some more light on the situation. The resource list is by no means exclusive and we welcome links to further information – just get in touch! There seems to be broad agreement on the benefit of planning, goal setting, adaptivity and decision-making in planned grazing systems. However, we find varying results, advice and conclusions throughout the evidence on the impact on animal and ecological productivity. Factions continue to exist and they tend to reproduce themselves through conventional literature review. 

Overall, there is a limited focus on the management of grazing methods in the collection and analysis of data. This makes it difficult to draw conclusions from the data as the success or failure of grazing strategies rely heavily on management and decision-making on each property.

So what do we do? Our advice – Speak to producers who work in different camps, different systems, different strategies – learn from those that have succeeded, and failed.

Refer to our previous posts here:

  1. Defining Grazing Systems: Continuous, Rotational and Time-Controlled
  2. Time Controlled Grazing: Strip, Cell, Rational, Savory +more

Positive +

Comparing the effects of continuous and time-controlled grazing systems on soil characteristics in Southeast Queensland – (Australian Journal of Soil Research, Griffith University, 2008)

This paper noted that short intensive grazing followed by long periods of rest – time-controlled grazing – has become popular across the world and amongst graziers in Australia. However, the authors stated that ” little research has been carried out on the impacts of this grazing system on the physical and chemical health of the soil.”

The researched focused on:

  • Field study on sheep grazing property south east Queensland (40km west of Stanthorpe). Long-term mean annual rainfall is 645mm with 70% in summer. Vegetation is native perennial grasses. Soils mostly clay to clay loam.
  • Property was a commercial property in the process of converting from long term continuous grazing to time-controlled grazing.
  • Compares continuous and time-controlled grazing over five year period, 2001-2006
  • 52 permanent sampling sites created.

The results included:

  • Increase in soil organic carbon and nitrogen in areas with time-controlled grazing as compared with continuous grazing, however longer time period monitoring is needed to draw firm conclusions.
  • Increase in ground little and no compaction
  • Nitrate and extractable P concentrations lower under time-controlled grazing

Results suggest that time-controlled grazing is superior in improving physical and chemical quality of soil, organic material, nutrient accumulation and plant re-growth – however, a longer time period is needed for statistically significant results.

Grazing management impacts on vegetation, soil biota and soil chemical, physical and hydrological properties in tall grass prairie – (Agriculture, Ecosystems & Environment, 2011)

This research wanted to better understand whether multi-paddock grazing is superior to continuous grazing. It focused on:

  • Evaluated impact of multi-paddock grazing at high stocking rate compared to light continuous and heavy continuous grazing
  • Neighbouring commercial rangers in north Texas tall grass prairie
  • Same management conducted on all for previous 9 years
  • Compared impacts on soil and vegetation

The findings included:

  • Bare ground highest in high continuous grazing
  • Soil aggregate stability highest with multi-paddock
  • Bulk density did not differ
  • Infiltration rate did not differ, but sediment loss greatest with heavy continuous.
  • Fungal/bacterial ratio highest with multi-paddock, indicating superior water-holding capacity and nutrient availability

Planned Grazing Enhances Pastoral Rangeland Productivity (Wilfred O. Odadi, Joe Fargione and Daniel I. Rubenstein – Land Degradation and Development, 2017)

The authors note that real-world assessment and trials around the efficacy of pastoral landscapes have been limited. To counter this, the research team here performed a landscape-scale assessment of the effects of planned grazing on vegetation, wildlife and cattle attributes across communally-managed Kenyan rangelands.

  • Rainfall in this area is generally low (annual mean 189-430mm), and there are peaks in April-June (long rains) and October-November (short rains).
  • The area is generally hot and the mean annual temperature is 16-33C.

The key findings were that planned grazing:

  • enhanced vegetation condition by 17%
  • 45-234% increase in herbaceous vegetation foliar cover
  • improved cattle weight gain by >71% during dry conditions

These results were surprising given that planned grazing had only been in place for five years, while unplanned grazing had been in place for decades. These improvements also occurred despite higher stocking rates on the planned grazing areas.

Effect of grazing on soil-water content in semiarid rangelands of southeast Idaho (Journal of Arid Environments)

This paper investigated the effect of grazing on soil-water content to understand better this important indicator of rangeland health. The research involved:

  • Treatments simulated holistic planned grazing, rest-rotation and total rest at stocking rates of 36, 6, and 0 animal days/ha.
  • Soil water content measured continuously from 2006 to 2008

Key findings included:

  • Grazing intensity varied from low (6 animal days ha−1) to high (36 animal days ha−1).
  • Soil-water content (%VWC) was highest in the holistic planned grazing pasture (HPG).
  • HPG used high intensity, short-duration grazing (6 days/year).
  • Percent litter cover was also highest under the HPG treatment.
  • Soil-water content varies in response to animal impact and the duration of grazing.

Ecosystem responses to cell grazing (University of Queensland, 2008)

Cell grazing has been generally accepted by pastoralists but has been criticised by some scientists. The aim of this research was to develop an understanding of the ecosystem response to cell grazing; it included a comparison with conventional grazing systems. The research involved:

  • Study sites paired where commercial scale cell grazing adjacent to conventional grazing
  • Across types and climatic variability in summer-dominant rainfall zone in northern Australia (Emerald (Qld), Wandoan (Qld), Moree (NSW), Katherine (NT).
  • Measurements of soil bulk density, microbial activity, perennial grass density and biological soil crust species, cover and distribution

Key findings included:

  • Compared to rotational grazing, the patch area index was tripled under cell grazing for the vertosol and doubled for the kandosol sites
  • Bulk density was significantly lower under cell grazing for the two vertosol sites
  • Continuous grazing system supported better developed cyanobacterial soil crusts closer to water compared to cell grazing.

The authors conclude: “The results indicate that, under a well-managed grazing enterprise and in a range of environments, a number of ecosystem parameters performed at a higher level under cell grazing compared to continuous or rotational grazing.”

Effects of time-controlled and continuous grazing on total herbage mass and ground cover (Journal of Agriculture and Rural Development in the Tropics and Subtropics, 2016)

Time-controlled grazing has been put forward as an alternative to continuous grazing, which has been documented to reduce pasture productivity and decline soil surface. However, little research had been performed on how time controlled grazing affected ground organic matter and land surface protection, which was the focus of this research. The research included:

  • Sub-tropical region of Australia – commercial property in southeast Queensland
  • 2001-2006
  • 44 permanent sampling location sites
  • Herd of merinos with different sizes in different grazing events (1,750 – 4577 DSE) moved between 21 paddocks
  • In time-controlled grazing, paddock grazed with an average of 12.3DSE/ha over 14 days (mean) and rested.
  • In continuous grazing, pasture stocked with constant ~1.6DSE/ha.

Key findings included:

  • Herbage mass under time controlled grazing increased to 140% in 2006 (compared to 2001). Outcomes higher where soil deeper and slope gentler
  • Ground cover under time controlled grazing significantly higher percentages in all years of the study
  • Ground cover increased from 54% to 89%

This study showed that time controlled grazing can increase total herbage mass and ground cover when compared to continuous grazing at similar stocking levels.

Neutral/Negative –

Cell grazing: lessons learned in trials across the NT over the last 15 years (NT Department of Primary Industry and Resources, 2016)

This webpage summarises the impacts of rotational grazing compared to continuously grazed paddocks across 4 trial locations in the NT:

  • Beetaloo
  • Newcastle Waters
  • Pigeon Hole
  • Douglas Daly Research Farm

The key findings were:

  • Rotationally grazed pastures did not stay in phase two growth during the dry season – they stop growing and become dormant
  • In three to six years of the trials, rotational grazing did not affect pasture yield, composition or soil carbon, either for better or worse, compared to continuously grazed paddocks.
  • Carrying capacity same as fully water continuously grazed paddocks
  • Higher operating costs and higher capital investment
  • Even grazing benefits, better cattle temperament, provides option for wet season spelling

These trial results suggest that fully watered continuous grazed paddocks with appropriate stocking rates perform as well or better than rotationally grazed systems. It is unsure whether the trial employed time-controlled grazing based on pasture available or just calendar rotations.

Better management of intensive rotational grazing systems maintains pastures and improves animal performance (Crop and Pasture Science, 2017)

This research was conducted as a result of the debate of the benefits of intensive rotational grazing and as few studies evaluated the contrasting management approaches of the systems.

An experiment was set up to investigate different stocking rates, paddock numbers and rest periods:

  • Cocksfoot as dominant species
  • Data collected on pasture composition and diet quality using faecal analysis, animal weight changes and pasture analysis.

They reported:

  • Animal production/ha greatest for fast rotations (56 days rest) at high rotations (13.6DSE/ha)
  • Continuous grazing equally productive
  • Flexible grazing on 3-4 leaf stage had lower stocking rates and was not as productive
  • Area of bare ground highest for the High Stocking Rate, continuous grazing treatment

Please note only the abstract of this research is available. The PDF costs $25 to purchase. We are unsure where this trial was completed or management strategies employed without access to full article.

HRM and cell grazing: a review of the evidence base (John McIvor, MLA, 2013)

Interest and debate around cell grazing and its merits, compared to other rotational and continuous grazing methods, is high. This review aimed to examine the evidence base.

  • Examined previous reviews of continuous and rotational grazing – 29 papers were assessed (6 from Australia and 23 from overseas)
  • Conducted a computer-based survey of peer-reviewed scientific papers that compared stocking methods.

Key findings:

  • There have been many comparisons of continuous stocking with various forms of rotational stocking over many years and the majority of these have shown that animal production from continuously grazed pasture is similar or greater than that achieved with rotational stocking.
  • Only one of the 11 studies that reported animal production found LWG/head was higher for Cell Grazing when stocking methods were compared at the same stocking rate.
  • There were 17 comparisons of herbage mass (12 at the same stocking rate and 5 with a higher stocking rate for cell Grazing); for two of these yields were higher for Cell Grazing with no difference for the other 15.
  • “This review of experiments comparing continuous grazing with Cell Grazing confirms the conclusions of Briske et al. (2008) that, in terms of plant and animal production, the experimental evidence does not show that Cell Grazing is superior to continuous grazing.”

The researcher concludes that “There is considerable anecdotal information of positive results with Cell Grazing that is not mirrored in the scientific literature.”

Investigating Intensive Grazing Systems in Northern Australia (Trevor Hall, MLA, 2011)

The author states that many beef producers are facing increasing financial and environmental pressures to remain productive and viable. Many are looking to more intensive grazing systems but are unsure of the costs and benefits. This project aimed to provide information on different grazing systems intensities in Northern Australia.

  • 9 properties selected, each operating under 2 of the 3 methods – continuous, rotational and cell
  • Paddocks monitored for pasture attributes, soil surface condition, grazing days harvested, diet quality
  • 2006-2009

The research found:

  • Trends in pasture condition were dominated by seasonal conditions
  • Trend for cell paddocks to have more spatially uniform ground cover
  • Diet quality generally lower in more intensive systems
  • No consistent difference in grazing days/ha
  • Integrated paddock management on the properties which explain lack of grazing system.

Researcher concludes that stocking rate management, rather than grazing system, is major driver of pasture and animal productivity.

Holistic Management: Misinformation on the Science of Grazed Ecosystems (International Journal of Biodiversity, 2014)

The authors state, “Holistic management (HM) has been proposed as a means of restoring degraded deserts and grasslands and reversing climate change. The fundamental approach of this system is based on frequently rotating livestock herds to mimic native ungulates reacting to predators in order to break up biological soil crusts and trample plants and soils to promote restoration.”

The authors address five assumptions of HM with a focus on western N American and semiarid ecosystems. They ask the following questions and review peer-reviewed literature in order to answer them:

  1. Do Grasses Senesce and Die If Not Grazed by Livestock?
  2. Does Rest Cause Grassland Deterioration?
  3. Is Hoof Action Necessary for Grassland Health?
  4. Can Grazing Livestock Increase Carbon Storage and Reverse Climate Change?
  5. What Is the Evidence That Holistic Management Does Not Produce the Claimed Effects?
  6. What about Riparian Areas and Biodiversity?

The author concludes: “This review could find no peer-reviewed studies that show that this management approach is superior to conventional grazing systems in outcomes. Any claims of success due to HM are likely due to the management aspects of goal setting, monitoring, and adapting to meet goals, not the ecological principles embodied in HM.”

Impacts of Rotational Grazing on Soil Carbon in Native Grass-Based Pastures in Southern Australia (Jonathan Sanderman et al., 2015)

The authors note, “Halting or reversing the decline in SOC in agricultural soils is seen as a win-win policy because of the dual benefits to soil sustainability/production and greenhouse gas abatement. Due to this fact, many nations are actively promoting management strategies that have the potential to sequester carbon.”

They state that the evidence to support improvement of SOC levels with the adoption of rotational grazing exists, but the field evidence for carbon sequestration is inconsistent. Therefore, this study sought to understand if rotational grazing (relative to continuous grazing) of remnant native grass-based pastures result in increases in SOC levels.

What did the research involve?

  • 20 landowners identified as having adopted rotational grazing practices in last 5-15 years in upper and mid-north of South Australia
  • Rainfall varies from 310 to 570mm / year
  • Pasture dominated by native perennial grasses (spear grass, wallaby grass) and annual grasses (wild oats, silver grass and brome grass)
  • 12 rotationally grazed paddocks were chosen based on: livestock had been managed consistently for at least 7-10 years, and nearby continuously grazed paddock on same soil type and landscape position was available.
  • Paddock information and management histories were collected
  • Climate data for 1980-2011 for each site extraced
  • Pasture productivity estimated using NDVI index
  • Refer to additional methodology steps in full paper.

Key findings included:

  • Reality is that there are a myriad of implementations of each of these management practices (rotational and continuous grazing).
  • Cluster analysis demonstrated that there is a group of farmers who practice a more continuous form of rotational grazing (e.g., lower stocking rate and more grazing days than other rotational graziers) or a more rotational form of continuous stocking (e.g., multiple or longer rest periods).
  • Pasture productivity, as assessed by the mean annual summed NDVI over the number of years of rotational grazing implementation, was no different between the two management classes
  • However, a significant positive trend suggesting that under rotational grazing productivity can increase relative to continuous grazing.
  • Productivity has been found to increase through the implementation of rotational grazing, from both a pasture and livestock production perspective, although the experimental evidence is mixed.
  • Across all sampled paddocks, there were no significant differences for SOCeq or SOC0-10between management categories.
  • A finding suggests that amongst the rotationally grazed sites the sites with the strongest grazing pressure showed the greatest SOC response

The authors conclude: “The evidence from this study suggests that in the short to medium term (< 15 years) measurable gains in SOC with adoption of rotational grazing in similar eco-climatic zones should not be expected to be observed. While we did not detect positive trends in SOC over time, NDVI data indicated that plant production was increasing slightly under rotational relative to continuous grazing.”

The intensity of grazing management influences lamb production from native grassland (CSIRO, 2017)

This research was conducted in response to the little attention the intensity of grazing management for optimal pasture/animal production in heterogeneous native grasslands in high rainfall zone of south-eastern Australia.

The aim was to determine how different stocking methods influenced productivity of a Merino ewe, terminal sire system, on native grassland. They compared continuous grazing through to flexible (4) and (20) paddock rotation systems.

Key findings included:

  • High per head animal production for 1 paddock than 20 paddocks – 4 was in the middle
  • 20 paddock system was able to run higher ewe numbers as it had greater food on offer
  • Organic matter digestibility highest in 1 paddock
  • 20 paddock systems allowed for retaining lambs after weaning to grow out.

Please note only the abstract is available so limited understanding of methodology could be garnered. Full PDF available for $25.

A global assessment of Holistic Planned Grazing™ compared with seasonlong, continuous grazing: meta-analysis findings (African Journal of Range & Forage Science, 2017)

This research was conducted in response to the claims that Holistic Planned Grazing can increase productivity and reverse climate change while doubling the stocking rate. This review aimed to compare Holistic Planned Grazing with season-long continuous grazing to explore the evidence for animal impact. The research involved:

  • Three quantitative meta-analysis models use to assess data sets from literature between 1972 and 2016
  • 75 data sets across Argentina, Australia, Canada, USA and Zimbabwe.

They found:

  • No difference in plant basal cover, plant biomass and animal gain responses
  • Two data sets from high and medium productions zones under sheep production had higher cover with holistic planned grazing.

This author concludes that “From the evidence available, Holistic Planned Grazing does not improve production and thus does not warrant the additional inputs (infrastructure and labour) that the approach requires.”

 


Where from here?

Feel more confused than ever?!

It is difficult to make conclusions from these papers as central to grazing management is the planning and decision-making framework and this doesn’t seem to be accounted for throughout much of the research. We agree with this statement from Kate Sherren and Carlisle Kent on how to move forward from this polarising debate:

“The grazing community should seek to expose and resolve competing understandings via transparent examination within the context of potential application, drawing scientists together with farmer experts and research users of various kinds.”

Have you come across any research or trial results? Please let us know and we will add to the discussion and the database.

We look forward to speaking and learning from producers who employ different strategies, both successfully and unsuccessfully. We hope the Farmer Exchange will aid in this discussion and the sharing of knowledge and experiences. Launching in the next weeks!

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