Improving Vegetation through Grazing Practices

Beef cattle breeding Breeding Dairy cattle breeding

If the vegetation present depends on pedoclimatic conditions, it also strongly depends on agricultural practices: it is possible to make the vegetation evolve so that it better meets everyone's expectations.

The principle of "grassland improvement", which consists of intensifying practices to select a productive and spring-flowering flora, is well known and practiced by breeders. However, its application to the entire farm generates difficulties.

The diversity of areas composing a parcel layout is an asset to offer a wide food availability throughout the year and facilitate the organization of grazing and mowing. But not all farms spontaneously have this diversity. Some need to build it to strengthen the technical and economic coherence of their breeding system.

Breeders generally rely on the spontaneous differences of their plots (environment and vegetation characteristics) to decide the role they will play in the grazing or harvesting chain (example: a productive and palatable plot for ewes at the end of spring, etc.).

But, conversely, breeders can also seek to make the environment and vegetation evolve (towards +/- productivity, or +/- seasonality, or +/- palatability, etc.) to succeed in making this plot play the expected role.

Making the flora evolve

Specify the characteristics of the present vegetation

This involves enriching the usual criteria for evaluating vegetation (productivity and nutritional value) with less usual but equally important criteria: food diversity, aptitude for deferred grazing, earliness and annual growth profile, speed of energy reserve accumulation, earliness of heading, relative variation of plant palatability during the year, variation of plant sensitivity to mowing or grazing during the year, etc.

A vegetation characterization tool was recently developed with breeders from the network, mobilizing recent scientific and technical work. It allows visualizing diversity in the parcel layout and understanding the links between vegetation and implemented practices. It proposes to locate each plot along 2 distinct gradients:

a productivity gradient of vegetation at the first cycle (the first growth of the year regardless of grazing or harvesting practices).
a gradient of related characteristics: speed of reserve accumulation, earliness of heading, aptitude for deferred grazing, ability to restart growth.

Some vegetation categories, quite frequently encountered on farms, have been identified along these two gradients. They deserve to be distinguished, as they can play very different roles in breeding systems.

Group of broad-leaved grasses of deep and fertile soils

on fertile to very fertile soils
broad-leaved grasses, high spring growth and rapid reserve accumulation
very low aptitude for deferred grazing: use a few weeks after growth

Groups of intermediate or fine-leaved grasses of moderately fertile deep soils

on soils of medium to high fertility
intermediate-leaved grasses, decent spring growth, fairly productive and fairly rapid reserve accumulation
medium to low aptitude for deferred grazing: use from a few weeks up to 1 month after growth

Groups of fine-leaved grasses of shallow and poor soils

on shallow, poor to very poor soils, in environments where nutrients or water are limiting
fine-leaved grasses, rolled, folded or hairy, with smaller stature. Medium to low productivity, rather slow growth
decent aptitude for deferred grazing: use up to a few months after growth

Group of broad-leaved grasses of poor to moderately fertile soils

in environments where one of the pedoclimatic components may be very limited: access to light, nutrients or water
productive broad-leaved grasses, rather slow summer growth, often late heading.
very good aptitude for deferred grazing: use up to 12 months after growth

Group of woody plants and graminoids of wet soils (permanent or temporary)

This group of plants is dual: woody (shrubs, bushes and trees) and broad-leaved, cylindrical or triquetrous graminoids (grasses, rushes, sedges) developing on soils with a permanent wet character (rushes for example) or temporary (molinia on marl for example)
slow growth, strong to very strong productivity for plants of wet environments
very good aptitude for deferred grazing in summer: use several months after growth; poor aptitude for deferred grazing in winter (deciduous woody plants or wetland species sensitive to frost)

Define the desired characteristics of the plot

When one wishes to create different vegetations to obtain varied characteristics at the farm scale, differentiated practices must be implemented according to the environmental context:

A first level consists of choosing practices to make the vegetation evolve with the limit of environmental conditions. A change in vegetation development (dwarfing, reproduction) or in its specific composition (survival) is expected.
A second level consists of choosing practices to make the environmental conditions evolve. A change in soil functioning, vegetation structures, soil water, environmental freshness is expected...

The vegetation characteristics desired must be specified according to the expected role of the plot in the farm. To define a realistic objective, practices to be implemented must be reasoned, evaluating their feasibility on the farm and their economic or labor cost.

Schematic representation of how to reason the practices to be implemented on a plot to make the vegetation characteristics evolve.

Make the flora and its characteristics evolve

Depending on the expected change in vegetation, different practices are favored or avoided. We illustrate here 6 changes often desired by breeders by presenting the mechanisms by which it is possible to impact vegetation and beyond the environment.

Slower growth, with better deferred grazing

The goal is to obtain a wider food availability throughout the year: slower growth of herbaceous plants, long leaf lifespan, good aptitude for deferred grazing. Also, one may seek to maintain productivity which could tend to decrease.

For example: to be able to mow even late without losing too much value; to have more palatable vegetation in summer.

How to achieve this?

Delay first use, rotate less quickly (long rest periods between two passes) and favor use outside growth periods, to allow later plants time to develop and accumulate reserves
Set precise entry and exit criteria for the plot regarding species to be consumed or left, setting desired harvest levels for each targeted species.
Gradually decrease soil fertility, by stopping spring nitrogen fertilization or stopping organic amendments, or by exporting organic matter, to disadvantage highly productive species in spring and allow light access for slower species.

Less dwarfed, more productive

The goal is to restore to the vegetation a growth capacity more consistent with environmental conditions on the plot.

For example: to regain a number of grazing days progressively lost on a plot.

How to achieve this?

Avoid continuous or long grazing during grass growth periods, to allow present species to rebuild their reserves after each use.
Reduce stay duration on paddocks in rotational grazing during grass growth periods to avoid plants restarting growth being grazed again.
In cases where flora has been replaced by pioneers (plants recolonizing bare soil), adapt practices to preserve seedling reimplantation of forage species (adapt or postpone grazing, stop mechanization, etc.).
Reduce impact of mechanical interventions (stop mechanization, soil compaction by machinery, seedling destruction by harrowing, acidification by amendments, etc.)

Faster growth and more productive

The goal is to obtain early start, high productivity and ability to restart growth throughout spring and autumn. The aptitude for deferred grazing is lost at the same time.

For example: to be able to return faster to the paddock in spring and autumn; to increase the stock harvested on this plot.

How to achieve this?

First use earlier, rotate faster (short rest periods between two passes) and finish paddocks to select herbaceous species quick to accumulate reserves by tiring slow ones.
Leave late spring growth in summer and late autumn growth in winter to allow reserve rebuilding.
Gradually increase soil fertility, by applying nitrogen fertilization at the beginning of growth period (mineral, fresh manure or slurry) or by significant organic amendments (composts), to favor productive species in fertile conditions (they grow fast and capture available light).
Mow herbaceous refusals during growth period to support fast species, mow woody plants to massively add organic matter, irrigate to extend growth period.

More homogeneous

The goal is to make part of the present vegetation disappear, to obtain better specialization of the plot.

For example: to avoid the back of the plot being neglected by animals.

How to achieve this?

Increase instantaneous stocking rate to prevent animals from choosing preferred species and impact different plants at the same time.
Specialize the plot for seasons that orient vegetation in the same direction (for example spring and/or autumn, late spring and/or late autumn, summer and/or winter).

More heterogeneous

The goal is to impact different parts of the vegetation differently to multiply food availability profiles on the same plot and also to make it play different roles.

For example: not to graze too much on bromegrass in spring so that it is available in late autumn or late winter.

How to achieve this?

Decrease instantaneous stocking rate to let animals express their dietary preferences.
Avoid specializing the plot to a single season to rely on different characteristics that gradually establish.

More diverse

The goal is to obtain more diversity in the cover, but without necessarily changing characteristics, to gain in palatability, dietary quality and medicinal value of the plot.

For example to let clover and birdsfoot trefoil express more in spring; to avoid one species remaining dominant.

How to achieve this?

Impact by grazing the plants tending to dominate, at the time they grow to limit light competition and penalize their reserve accumulation, limit litter in spring to lighten later plants.
Allow slight variation of practices from one year to another to give opportunity to different species to develop.
Move away from extreme environmental conditions (very high fertility level, very dense shade, soil without water reserve).
Seek stabilization of the environment, around a balance between vegetation, climate, soil and practices, to avoid causing massive mortality of some plants due to practice changes.
Limit impact of mechanical interventions (uprooting, soil compaction), reduce or stop mineral nitrogen fertilization.

Autres fiches Pâtur’Ajuste

Sources

SCOPELA, with the contribution of breeders. Technical sheet of the Pâtur’Ajuste network: Making vegetation evolve through practices. April 2018. Available at: https://www.paturajuste.fr/parlons-technique/ressource/ressources-generiques/faire-evoluer-la-vegetation-par-les-pratiques