Pasture assessment

What is a pasture assessment?

The aim is to establish the number of species present in the pasture. Generally speaking, there are three large families of pasture species:

Required productive species:
- Grasses or Poaceae
- Leguminous plants ou fabaceae
Low production, non consumed, or toxic species
Other varieties : non leguminous, and non graminae varieties.

Here are some plant determination examples carried out by Leconte D. et al 2015. In some studs, where free grazing is adopted, the pastures are seriously deteriorated ( with an average presence of 48 % of other varieties).

	Normandy pastures (all types of animal species)	Merlerault Stud farm		North-eastern France	Plains in Orne department (61)
Type	Average	National stud	Private stud	Private stud	Private stud
Year	2002 à 2010	2010	2008	2004	2014
Number of plots	406	11	20	20	11
Total number of Poaceae	54,5	58,5	55,8	42,6	71,5
Total number of Fabaceae	12,1	10,0	6,7	9,0	7,4
Total number of other varieties	33,5	31,5	37,5	48,5	21,1

Why should a pasture assessment be carried out on fields grazed by horses?

Fields used only to graze horses frequently present the following signs : overgrazed areas, rough areas, bare patches due to trampling of feeding areas and frequent passageways.

Horses grazing behaviour, i.e selecting feeding areas, is damaging to field vegetation as it induces:

Invasion of overgrazed areas by undesirable rosette plants, which are not eaten, and have no forage value (daisies, dandelions, plantain, annual bluegrass).
Colonisation of rough areas by high development species (Velvet grass, orchard grass, and other). These species could be consumed, but are left uneaten and used as defecation areas.

What is an ideal production for fields used for grazing horses?

Areas for promoting grass production as a horse feed

Grass and hay cover 90 % to 100 % of a feed ration for horses with high needs, when the sward is of good quality, and quantity. For animals out to grass, or on fodder, a pasture rich in high quality forage plants ( with high nutritive and productive values) is required.

Pasture assessment enables to direct maintenance and renovation practices, in order to preserve the quality of the field sward.

Areas used to turn horses out, or used through the winter.

For these areas, termed « paddocks », the grass cover is not used for feeding the horse. It is considered more of an outdoor recreational area, exercise area or outdoor accomodation area. Maintaining a grass-producing area which is not deteriorated by weeds (non-consumed and undesirable) is an illusion.

For these surfaces, if you wish to maintain a grazing area, you will need to maintain a grass cover by eliminating weeds (chemically or by mowing) to avoid invasion, and to avoid the appearance of totally bare patches. Overseeding, when done every year, can be a costly process. It is better to consider stabilising a surface with an inert material, if the priority is a recreational area, rather than trying at all costs to maintain a green plant cover, which will turn into a mud field in winter.

Overseeding with aggressive species (fast growing species) such as Italian rye-grass (festuca perennis) and resting the area, are the only ways to restict total deterioration through trampling.

Why should a pasture assessment be carried out ?

When and where should it be performed ?

The diagnosis should preferably be conducted in the spring, when the grasses are most identifiable.

Analysing the farming methods of the pasture

Firstly, the general aspect of the sward and the soil should be observed. Fertilisation practices and history, farming practices (grazing or forage production), and utilisation modes (presence of animals and grazing load) should then be recorded, as well as the production aims of the plot.

Method used to collect plant samples

Quadrat utilisé pour le diagnostic prairial — Quadrat used for field assessment © C. Geyl

The methods used for sample collection of the sward to be analysed are numerous:

Quadrat Method (photo)
Square meters, or handfuls, or « dominant unit station » of a 0,25 acres plot. For the station, around 30 handfuls of grass, representing 25 sq cms, are collected. In each handful, the abundance of each variety is noted, and the family and species are determined.

Tools provided by the GNIS (Groupement national Interprofessionnel des Semences / National Interprofessional group for farming seeds)

The GNIS has established a fact sheet describing how to observe the plants in a specific location, this fact sheet contains:

Plant diagnosis grid
Determination key for grasses (graminae)
Classification sheet of different species

Results of the assessment

The assessment gives an estimation of the distribution of each species in the biomass studied. Frequency, abundance and dominance percentages are calculated per species. The species are then referenced according to their forage quality, and as indicators of the environment. This analysis, usually carried out by an advisory technician, is to help the farmer think about how he manages his pastures. The plant diagnosis assesses appropriate maintenance and /or renovation methods to be implemented for the pasture.

Classification of forage species

Forage quality index

Plant species are qualified by a forage quality index. This index measures productivity and nutritional value. Forage classification, then differentiates species as follows : GOOD, AVERAGE, and MEDIOCRE.

Below is a non exhaustive list of species graded according to their forage quality (from : Hubert & Pierre 2003).
	Species with a good to very good index	Species with an average index	Species with a mediocre to non-existant index
Poaceae (grasses)	Timothy grass, Perennial ryegrass, italian ryegrass, orchard grass, High fescue, meadow fescue, Rough bluegrass, Kentucky bluegrass	Agrostis stolinefera, Agrostis canina, Couch grass, Field meadow foxtail, Avenula pubescens, Yellow oatgrass, Red fescue, Velvet grass	Sweet vernal grass, soft brome, Crested dog’s tail, sheep fescue, Glyceria fluitans, creeping soft grass, annual bluegrass
Legumes (Fabaceae)	Bird’s foot trefoil, Marsh bird’s foot trefoil, Medick, Purple clover, White clover	Meadow vetchling, Strawberry clover, Lesser trefoil, Bird vetch )	Restharrow (Ononis spinosa
Other varieties	-	-	Yarrow, Ribwort plantain, Dandelion

Plants as environmental indicators

The « ecological » index (DEVRIES as quoted by Hubert & Pierre 2003) summarises pasture plant behaviour according to their environment. The index is very high when the plant grows in a specific environment.

Environment	Plant species
Good soil fertility	Perennial ryegrass, Kentucky bluegrass, Timothy grass….
Bears up in poor soils	Kentucky bluegrass, creeping soft grass, Yarrow, cuckoo flower….
Likes a humid environment	Glyceria fluitans, Agrostis canina, Black sedge,..
Bears up to acidic soils	Velvet grass, Cuckoo flower, Sweet vernal grass, Yarrow….
Resistant to mowing	Perennial ryegrass, Kentucky bluegrass, Rough bluegrass, Crested dog’s tail, Annual bluegrass, White clover, Common daisy….
Resistant to grazing	Perennial ryegrass, Meadow fescue, Orchard grass, Crested dog’s tail, Field meadow foxtail, Agrostis canina, White clover, Yarrow, Common daisy….

Conclusion

Whatever the animal, it is important to ensure a balance between forage production and herbivores’ needs, by adapting the grazing load throughout the season.

Horses create a heterogenous space, which constantly needs correcting through localised fertilising of overgrazed areas, when possible associated with mixed grazing, and by shredding the smaller rough areas, or cutting for hay when the roughs are substantial.

A mediocre pasture can in time reach a satisfactory productive level, by overseeding in addition to these gentle improvement measures. These techniques preserve the plant cover already present. In this way, the plant composition of permanent or temporary pastures can be maintained to ensure longevity.