Assessing the amount of grass available – grass cover

Grass cover is the average quantity of grass in kg DM/ha to ground level and includes the grass available for grazing and that which will be left after grazing. In this booklet grass covers are presented to ground level, and should not be confused with grass cover in the Republic of Ireland, which refers to grass available over 4 cm in height.

A number of methods have been developed to assess grass cover

A rising plate meter can be used to measure grass covers until sufficient experience is gained by visual assessment. It relates pasture height and density to yield through a carefully calibrated equation.

The rising plate meter consists of a thin aluminium plate connected to a shaft by a gear linked to a read out of grass height. A mechanical counter records the number of readings from an area.

As the rod is lowered into the pasture, the plate is supported at a height determined by the sward’s density and height. A procedure for using the rising plate meter and calculating average farm cover is outlined at the end of this chapter.

Target grass covers are set pre- and post-grazing for various times during the grazing calendar and for different types of stock. Refer to the various livestock sections for more information.

Assessing grass covers in the field using the rising plate meter

Assessing the sward height alone is not a true reflection of grass yield. When visually assessing swards or ‘eyeballing’ as it is often called, sward height and density must be considered. Dense swards, for example a ryegrass/clover sward grazed regularly by sheep, will contain a greater amount of grass than an erect open sward grazed by cattle at the same height.

Estimating grass cover in a field can be difficult when swards are grazed unevenly as a result of poaching, spoilage and/or contamination with urine or dung. However with experience an overall average can be assigned to the field.

Examples of grass covers are presented in the photographs below. The wellie boot has been used by farmers as a rough guide to assessing grass covers.