Grass - a deeper look

Grassland covers much of the UK.

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It is divided into two types:

  1. Permanent. Which is never ploughed, at least for intervals of 20 or more years.
  2. Temporary. Which is ploughed at intervals from 2 to 10 years.

Both have almost as many subdivisions as farms, but typical ones are:

  1. Unimproved. Always permanent and where negligible amounts of fertiliser, sprays or management has taken place. Often described as 'hill' or 'rough grazing'. Usually found where the soil is thin, steep, rocky or of low productivity. Covers much of the upland west and small areas elsewhere where land use has prevented improvement (eg some military and crown lands) or landowners have wished to preserve the old ecosystem. A few unimproved river meadows can also be found. Typically it contains rare plants specialised for the particular ecosystem and environment. Highly unproductive agriculturally.
  2. Permanent. Where ploughing or other soil moving operations are rarely done (typically under once per generation or never). Can vary from an occasionally ploughed version of unimproved to highly productive and well managed grassland. Usually has a wide range of grass species, and often broad leaved weeds as well although these may be periodically sprayed when they get excessive. Often, due to a good soil structure and a range of grasses and strains, intensive permanent pasture can take a lot of abuse.
  3. Temporary Grassland (Leys). Typically of 2 to 3 year (but can be 6 to 10 or more) duration interspaced by arable cropping. Common in the south and east where there is significant arable. Typically less able to withstand abuse than permanent pasture.

Grass species

There are thousands of grass species but very few are ever used agriculturally. Coltsfoot, timothy and various fescues may be used on rare or specific occasions but by far the major species is ryegrass which probably comprises 99% of grass seed used. Ryegrass comes in four groups, which are really a continuum.

Most UK perennial ryegrass has been bred from 'improved strains' developed by MAFF at Aberystwyth from selections of wild strains taken from natural high yielding grassland in the 50's.

  1. Italian Ryegrass. A high yielding continental species of poor persistence it is often used for short leys of 1 to 3 years.
  2. Early ryegrass. Heads in mid May. Usually moderately persistent, high yielding and often with poor late summer yields and feeding quality but good spring growth.
  3. Medium ryegrass. Heads later than (1), usually late May. Usually quite persistent and quite high yielding and often with moderate late summer yields, early growth and feeding value.
  4. Late ryegrass. Heads later than (2), often into July. Usually very persistent and often with good late summer yields and feeding value but poor early growth.

There is also annual ryegrass. One variety, Westerworth's, is almost unique in seeding in the year of drilling when drilled in spring. Very unpersistent (one yr max) and rarely used in the UK.

Management and Yields

Grassland management often differs markedly from farm to farm and even within a farm. Because a fertile productive grassland can utilise a vast amount of nitrogen (over 1000kg/Ha) nitrogen application rates can vary from none to 500kg/Ha or more, largely depending on the potential or required productivity. Unless fertiliser or animal manures are wrongly applied the highly active topsoil (particularly for a long or permanent ley) makes leaching surprisingly low. Phosphate is generally applied to match the takeoff by animals or silage. Potassium in the soil is pretty well stripped out by grass, and is effectively all removed in a hay or silage cut but is recirculated back via urine when grazed or when manured with dung or slurry.

Pesticide usage on grassland is low. Often fields can go for decades without being treated with anything although periodic (often by hand) herbicide spraying is usual. Insect pests are confined to leatherjackets (tipulidae - daddy longlegs), which selectively graze ryegrass, and can cause heavy thinning of swards and replacement with unproductive or weed species (typically annual meadowgrass and weed fescues). Periodic spraying to control leatherjackets is required (perhaps every 3 to 10 years) in some parts of the country (typically south and east) when infestations reach monumental proportions.

Long leys and permanent pasture contain huge numbers of arthropods in their soils. Often measured in 10's or even 100's of tonnes/Ha. Whilst most of these cause only a modest yield loss (estimates of 10-20%) their grazing can devastate a new ley where seedling grasses are often only 1/100th the mass of arthropod grazers present. Insecticides can only reduce this effect. Consequently leys are often switched to arable for a year or two to reduce the pest burden before re-seeding. Even so arable crops following leys frequently require insecticide protection (eg for wireworm - click-beetle larvae) to establish properly.

It is unfortunate that the high nitrogen levels (mostly bacterial protein) in the soil of long leys (and particularly those with a lot of clover) liberate vast quantities of nitrogen when ploughed into an arable crop which mostly leaches into watersupplies.