White clover (Trifolium repens) is New Zealand’s most important pasture plant, due to its nitrogen-fixing abilities. It is sown throughout the country and grows well on fertile soils, but struggles in dry areas. However, pasture clover content is normally low – usually less than 10%. White clover is recognisable by its white flowers.
If a newly sown pasture isn’t grazed for up to six weeks from December until late January, then the clover will seed, and this seed crop can yield up to 50 kilograms per hectare. That’s 70 million seeds per hectare or 7,000 seeds for each square metre. Clover seeds develop an impermeable coat and can live for centuries in dry soil. Some clover seeds were recovered from under a 700-year-old church in England – and they germinated.
The clover root weevil (Sitona lepidus), which attacks white clover, was accidentally introduced to New Zealand in the 1990s and has since spread throughout the North Island and into the South Island, reducing pasture clover content. A parasitic wasp released in North Island during 2006 to control this pest appears promising.
White clovers with a dense mass of stolons and many small leaves are the most persistent because stolons spread, develop roots and split into plantlets, each eventually forming a separate plant. These types survive well in pastures closely grazed by sheep.
Large-leafed clovers have erect growth, large roots and flower heads, and thicker, but fewer, stolons. They are used in dairy pastures where grazing is relatively light and infrequent.
Small-leafed and large-leafed types are often mixed together to maintain good clover content for grazing and nitrogen fixation.
There are also medium-leafed types, which grow well in a broad range of grazing situations.
Each stem (or petiole) of a clover plant usually has three leaves, so if you find a rare four-leafed clover it is supposed to bring you good luck. These are different from a shamrock, which always has four leaves.
Red clover (Trifolium pratense) has a red flower, hairy, dull foliage, and a taproot. It is slower to flower than white clover. It can last up to seven years under favourable conditions – such as lax grazing or under long summer grazing rotations – but does not tolerate close grazing. When sown, it is important to ensure that it establishes itself well, as it does not reseed readily.
Red clover grows well on fertile, drier soils with other grasses, clovers and herbs. It makes good silage and hay. Deer prefer it to other plants, and it is acceptable to all livestock.
Red clover sometimes contains enough oestrogen to lower sheep fertility when fed in autumn, during mating; however, recent selections contain much lower oestrogen levels.