Enhanced Grassland

Enhanced Grassland "Window of Opportunity"

Introduction

FAO 2023 Global Assessment of Grassland SOC highlights that current grassland management trends are leading to SOC losses ….. After oceans, soils are the second largest carbon pool on Earth and they play an important role in global climate change due to the large amount carbon currently stored in soil organic matter.

The Global Monitoring Laboratory shows a 6 PPM seasonal variation in atmospheric CO₂.

The starting point for my literature review recognizes that photosynthesis is the primary mechanism for atmospheric carbon accumulation, a “window of opportunity” for enhanced peak photosynthesis and Carbon Dioxide Removal (CDR).

This also recognises that any plant shrub or tree that cannot come back from intensive defoliation will require replanting so therefore, SOC accumulation will not be continuous and compounding. Forest carbon accumulation becomes neutral at plant maturity and pine plantation SOC accumulation will be terminal at plantation harvest.

For biomass carbon to be not prone to atmospheric emission, it has to be in the ground.

So on that basis, perennial grassland is the only option that can deliver a continuous and compounding carbon pathway to the subsoil for CDR.

These studies identify animals as being problematic to grassland CDR (Cory Matthew 1986) (Moot DJ 2021) (McSherry and Richie 2013) ……… in a global review of grassland grazing studies found that increasing grazing intensity increased SOC by 6–7% on C₄-dominated and C₄–C₃ mixed grasslands, but decreased SOC by an average 18% in C₃-dominated grasslands.

It appears that the studies in general show no apparent focus on enhanced peak photosynthesis “window of opportunity” To frame the “window of opportunity” starts with intensive defoliation to allow sunlight at the base of the plant, for new tiller initiation and peaks with the onset of reproductive maturity. The observations in (Moot DJ 2021) show that any interruption to the growth cycle will reduce root to shoot ratios due to reduced root nutrient partitioning prioritizing leaf recovery.

My review has identified seasonal extremes in grassland production as the origin of grassland SOC losses.

The grassland utilisation paradox

The Rate of Growth table below seriously understates how the extremes of spring surplus to summer / autumn production deficit are central to under and over grazing at all the wrong times leading to the grassland SOC losses identified above.

Both extremes of utilisation are equally disruptive to the “window of opportunity” for enhanced green leaf area for sunlight interception and carbon accumulation.

Condensed from the observations of R. M. McNamara (1992) (Windsor)

Seasonal Biomass Productivity

This is the Rate of Growth record over an eleven year period in North Otago.
26 defoliation methodology is a fair representation for net primary productivity (NPP) variability but not for total NPP on a seasonal basis.
If the spring quarters was moved forward by two fortnights and disregard the two poorest seasons, the spring normal becomes two thirds of the annual production.
Unutilised summer surplus results in a buildup in reproductive residue. Invariably, this residue will result in a trend of the default species becoming the dominant species via the persistent, space invading lignified tissue.
Grazing the regrowth is unavoidable in a dry trending environment. To maintain vegetative cover in most summer / autumn periods is incompatible with animals.

Moot DJ 2021 “When plants are C-limited after defoliation they initially use root and pseudo stem reserves to recover their leaf canopy. If defoliation occurs again before reserves have been fully replenished the plants will prioritise shoot growth over roots. This reduces their root: shoot ratio and increases their susceptibility to any additional water or N deficiency. When water or N limitations occur, plants favour root growth over shoot growth. However, this limits C availability so too frequent or intensive defoliation will reduce pasture resilience. Perennial ryegrass is particularly sensitive to multiple stresses due to a lack of perennial storage organs”

These production extremes show that under and over grazing at all the wrong times in the dry East Coast of New Zealand is unavoidable so therefore an overall degenerative grassland trend with animals is inevitable.

Enhanced photosynthesis “window of opportunity”

As a starting point for this discussion to minimise the autumn degenerative trend, I would suggest that from longest day till shortest day, I propose a long rotation of somewhere between 120 – 180 days, that being seasonal dependent.

If 20% of a given area of harvestable grassland was committed to a program of zero Grazing with Intensive Defoliation at Stem Elongation (ZG/ID@SE) for a two year period starting at autumn equinox under the MPI RMA Farm management plan,’ that would allow a ten year return cycle.

A two season period of ZG/ID@SE will capture enhanced peak photosynthesis, making grassland more resistant to SOC loss with environmental extreme and more tolerant of current animal performance priorities.

The huge feed buffers that ZG/ID@SE would create will make animal production more tolerant to environmental extremes, but will require advanced pasture harvesting and storage techniques.

The ZG/ID@SE defoliation timeline that I have prescribed below will deliver on seasonal diversity. The dominant regenerating species will be seasonally strategic and in each case, intensive defoliation is central to clearing the way for enhanced photosynthesis of the dominant species in the subsequent season.

Predicted defoliation deadlines;

Spring equinox plus 30 days. Early interruption to primary seed head development is strategic because secondary seed head is less vigorous allowing later maturing species to compete.
Longest day plus 30 days releasing species that are more competitive for limited moisture and nutrient. Alex Williams (2019)
After opening rains in the month of autumn equinox. This defoliation will be different because there will be very limited stem elongation and the vegetative cover will be showing signs of significant environmental stress. Leaf die back is a very strategic protection mechanism of the plants vital organs so premature grazing by animals is not helpful. Leaf die back is strategic to limiting soil temperature increase which is prone to increasing soil moisture loss. The photosynthate requirement is relatively small compared to the Microbial Associated Soil Organic Carbon (MASOC) driven exudate production.

The most competitive vegetative early season species contribute more to rhizodeposition (SOM) Early defoliation will release species that contribute more to MASOC ecosystem functioning that converts the SOM to more plant available nutrient, particularly under environmental stress and nutrient limitation. Products of MASOC are more resistant to atmospheric emission long term. (Noah W Sokol 2019) Markus Lange (2020)

A detail lacking in a lot of these studies is how they maintained enhanced photosynthesis. I believe that it would be fair to say that animals were not a feature in any these and other studies. A.M. Raiper (2024) Indrani Sharma (2023) 48, 49, 51, 65, 76, 78, 79,

SOM and grazing management are big predictors of increasing or decreasing Water Use efficiency (WUE) and Carbon Use Efficiency (CUE). (McSherry and Richie 2013)

The selective grazing habit of sheep and cattle is normal, leading to under and over utilisation at the same time. Both are equally disruptive to photosynthesis sunlight interception. There is no in between. Invariably, the residue that develops will result in a trend of the default species becoming the dominant species via the persistent, space invading lignified tissue.

The default species can be the preferred species meaning that it is not a species problem. Reproductive residue is a management problem, not a species problem.

Every autumn, there are thousands of hectares on the dry East Coast of New Zealand with varying amounts of lignified reproductive residue cover and the recovery management from this aftermath is less than prescriptive.

My observations show that for the sake of a one off autumn burn off, farmers can impose a speedy implementation of enhanced photosynthesis in traditional grasslands (read; default species dominant) because the vegetative dominant species and species diversity feature will still be present. They just need the opportunity to compete.

One scenario could be an immediate emergence of a large population of annual species grasses in spite of a good population of perennial species as can be seen ten days after the opening rains subsequent to a typical brown summer. This is a real possibility in an established pasture aged years 3 – 5. Overgrazing in the autumn leads to bare ground. Bare ground in the autumn will be more likely inhabited by an annual species seedling in the spring time than by a perennial tiller. The annual species requirement to reseed means that it will not persist, given early interruption to reproductive maturity.

Three ZG/ID@SE defoliations annually imposing early interruption to reproductive maturity will quickly control their dominance and strengthen the competitive perennial diversity perspective. Jana S. Petermann 2021.

Based on the observations of (Cory Matthew 1986), who found that mechanical harvesting at anthesis enhanced root development over all grazing timing and intensity options. Applying logic to this observation would suggest that the deep SOM resulting from the extended period ZG/ID@SE can be sustained and further enhanced by ………. extending the vegetative period and capturing delayed anthesis.

This will make grassland more tolerant of current animal performance priorities and increased feed conservation will make animal production more sustainable.

To the question, where do the animals really fit in this? That really depends on how sector engagement develops. Sector must speak up on ETS.

From shortest day to longest day, animals have an extremely valuable, but limited place in our sensitive and fragile environments for mitigation of;

Port Hills fires. Lake Ohau fire. Bluff fire. Destocking many DOC grassland areas of natural significance does not necessarily enhance the objective if it increases the risks due to fire and default species dominance. One grazing rotation after opening autumn rains and one rotation defoliation knock down late spring will maintain vegetative cover promoting species diversity instead of the dominant default species with combustible fuel buildup.

Cyclone Gabriel Cyclone Bola. East Coast North Island hill country is in urgent need of a robust grassland management that can cope with increasing extreme autumn weather events of this magnitude. Destocking longest day to shortest day will enhance autumn vegetative cover that will hold back a lot of hill country sediment that was problematic for low country farms, businesses and home owners.

Animals need to be managed onto intensively grazed grassland that are unharvestable due to steep terrain or obstacles such as rocky outcrops, natural water course and bush cover that can be destocked longest day to shortest day.

If we apply logic to the observations of Moot DJ 2021 and then apply that to this Google image would suggest that any early defoliation of the primary growth units will compromise peak BGBNPP.

This Google image illustrates the two limitations to photosynthesis for grassland above and below ground biomass NPP, being;

Continuous defoliation of the primary growth units and
Senescent tissue build up interrupting sunlight interception. at the base for plant regeneration.

At stem elongation, root nutrient peaks and becomes increasingly committed to seed set, reproductive maturity and plant senescence. Early interruption to reproductive maturity at stem elongation by intensive defoliation will capture peak carbon accumulation and promote vegetative regeneration with minor interruption below ground biomass NPP. (Cory Matthew 1986)

Because of the difficulty in quantifying BGBNPP, a seed in a pipe technique appears to be the go to methodology.
Deferred Grazing handbook (2020).

This is a good illustration of Below Ground Biomass Net Primary Productivity (BGBNPP) from reduced defoliations.

What this shows is that biggest below ground accumulation differential is at depth which will be dependent on enhanced / peak photosynthesis.

The table below has been modified from the observations of Nielsen (2021) quantifying Below Ground Biomass Net Primary Productivity (BGBNPP) and stubble NPP of the zero cut were both ~ three times greater than the five defoliations across three species. Above Ground Biomass Net Primary Productivity (ABGNPP) was about the same for the five cut Vs zero cut, however the five cut received five times the amount of artificial N. Total NPP of zero cut over the five cut was nearly 2.5 times greater.

The problem with these studies is that they do not replicate mature grassland characteristics. They are observations of juvenile plants where there will be no inclination to go reproductive in the first season,

If the seed had been germinated the previous season, it would have partially overcome the juvenile factor. But better than that would have been a core sample of established grassland pasture.

Also inappropriate is imposing intensive defoliation on a juvenile plant and can be seen in the deferred grazing study image Vs rotational grazing.

Conclusion
Photosynthesis is the primary mechanism for atmospheric carbon accumulation. A “window of opportunity” for enhanced peak photosynthesis and Carbon Dioxide Removal requires strategic defoliation interrupting plant reproductive maturity and senescence carbon pathway to atmosphere, facilitating new green leaf area for sunlight interception and ongoing above and below ground carbon accumulation.

Enhanced Grassland