Clover can cut fertiliser requirements provided it is managed correctly and artificial fertilisers are used carefully
Adding white clover to leys to cut grassland fertiliser bills continues to be a popular strategy for livestock farmers. A well-established grass-clover sward can supply the equivalent of about 150kg/ha of nitrogen.
However, for clover to establish successfully and remain in the sward, attention to agronomy and an appreciation of the plant’s requirement for light and space is needed.
Clover is more sensitive to soil nutrient status than grass, so ensure a pH of 6-6.5 and P and K indices of at least two, explains GrowHow’s Elaine Jewkes.
“Soil-testing one quarter of the farm every year will highlight where any nutrient shortfalls or pH adjustments are needed.” she says. “When sowing clover, nitrogen should not be applied, except for on low N status soils, where a maximum of 50kg/ha N may be needed.”
Clovers need warm moist soils to germinate – so spring sowing where soil temperature is rising is ideal, although sowing can be done anytime before late August if adequate soil moisture is available, adds Limagrain’s Ian Misselbrook
“Clover should be sown close to the surface – so, for best results, slot-seed or over-sow with a grass harrow and seedbox. In addition, better germination rates and early vigour can be obtained using seed treated with a bio-stimulant like Headstart, which then gives clover better competitive ability against existing grasses.
“The most significant difference compared to managing grass is that clover has a high reliance on light and space to grow,” explains Mr Misselbrook. “So, for its survival in a grass sward, it’s essential companion grasses are not allowed to crowd it out. This makes clover easier to retain in grazing leys where an open sward can be maintained, than in silage leys.
“Ideally, clover should always be sown with grass mixtures containing a high proportion of tetraploid varieties of ryegrass. These tend to be less prostrate than diploids and so interfere less with clover growth. Never sow clover into short term leys which have been heavily-fertilised as this encourages grass growth at clover’s expense.
“Clover seed can be bought either as a single variety, or as a blend of varieties with differing leaf sizes. Blends will always adapt better to changes of management, livestock and climate than straight varieties. They should be selected according to how the ley is to be used and/or what livestock are to graze the sward.
“Sheep are selective grazers and so clover blends should contain some large leaved varieties to serve as decoys while the small leaved varieties establish. In fact, it is good practice to take sheep out of leys during the vulnerable early stages of clover growth where plants have only a tap root and have not yet developed stolons.
“For rotational grazing for cattle, choose clover varieties with medium and large leaves that will compete better with the longer grass sward.
“For silage swards, again choose blends of medium and large-leaved clovers – these give the best herbage yields and stand tall above grass to take light and space. But when coming up for second cut, don’t let grass get too long or it will shade out the clovers.”
In established grass-clover swards, weed control and fertiliser applications also require a different approach to grass-only leys.
“For grassland herbicides which are clover-safe, timing of application is particularly critical. Where herbicides are not clover friendly, seed should only be oversown once a weed-free sward has been obtained, and according to the herbicide manufacturer’s recommendations on when it is safe to sow post-spraying,” explains Mr Misselbrook.
Since clover starts growing later than grass, a modest application of nitrogen in the spring, up to 50 kg N/ha, may be used to encourage some grass growth to fill this “feed gap”, says Ms Jewkes.
“Modern clover varieties can tolerate modest amounts of N fertiliser during the season, but farmers should be aware that any application of nitrogen in the clover’s immediate environment will cause the nitrogen fixation process to be suspended. When clover dominance occurs then application of nitrogen will encourage the grass in the sward to recover and out-compete the clover.”
CAP: The most significant difference compared to managing grass, is that clover has a high reliance on light and space to grow.
BOX: See this week’s Arable and Forage crop nutrition special for more on managing fertiliser and manures