What are the main priorities for successful kikuyu management?
- keep kikuyu leafy and do not allow stem or stolon to develop. This will maximise pasture quality.
- keep rapidly growing kikuyu paddocks on a faster round to avoid shading out better pasture species. Well managed kikuyu has a good content of white clover
- Control summer kikuyu with mowing or mulching if needed – do not allow a mat to develop
- Mulch in the autumn to ground level, use vertical blades to cut stolon’s and slow kikuyu growth
- Drill hybrid or Italian ryegrass at 15-20kg/ha in April following mulching
What is the pasture intake from kikuyu?
Milking cows will harvest about 1200 kg DM/ha each grazing from a kikuyu pasture regardless of the amount of DM on offer.
This amount represents the re-growth from the last 4 to 5 young green leaves.
The remaining material will be stem and senescent material which has accumulated both from earlier grazings or has developed since the last grazing if the rotation length is too long.
This material is not worth the effort of the cows harvesting it for milk production.
How does poor pasture utilisation lead to a kikuyu mat?
Kikuyu has a stolon which becomes long and has poor feed quality, making it more complex to manage than ryegrass. The tip of the stolon will have young, high ME leaves but further down the stolon the leaves are older and lower quality. Therefore, kikuyu declines in quality as it accumulates dry matter, and the faster it is growing the quicker it will lose quality.
For example: If kikuyu is growing fast and a farm is on a slow rotation and the cows leave kikuyu behind then these unutilised parts of the plant will remain in the pasture and the stolon will extend to grow new leaf. This newly grown leaf is productive but the old leaf and the unutilised stolon will be low quality and will not be eaten by the cows at the next grazing. This is how a mat of kikuyu develops, overtime if left a kikuyu mat will build up to gumboot height and climb fences.
This mat of poor-quality pasture will shade out winter active pasture species. Removing this mat before winter allows these species to establish and become dominant to fill the late winter/spring feed gap frosted kikuyu creates.
Removing a thick mat of kikuyu requires mulching – using cows to hard graze kikuyu will cost liveweight and can create animal health impacts.
Can good heifer growth rates be achieved on kikuyu?
Yes, well managed leafy kikuyu provides good summer feed for growing young stock, with less grass staggers and facial eczema risk than ryegrass pasture. However, maintaining feed quality is tricky – and requires good management. Young stock need to be kept moving and not be used for pasture control. Having smaller paddocks and more frequent shifts helps with pasture management.
Where mulching and/or mowing is not practical running another class of stock can help manage summer and autumn growth. Breeding cows or carry over cows can graze behind the heifers to keep pasture quality.
Take advantage of winter and spring growth so you are less reliant on autumn weight gain. Salt supplementation is needed.
Should I use nitrogen and if so, when?
Kikuyu responds well to good soil fertility and will not tolerate low soil fertility environments. Kikuyu can respond rapidly to nitrogen when conditions are favourable for pasture growth (i.e. warm and wet). Nitrogen may have a place in increasing early summer yield, encouraging kikuyu to dominate pasture, especially in increasing slow growth in January. If moisture is limiting (e.g. drought) kikuyu will not respond to nitrogen.
Nitrogen should not be applied to a kikuyu dominant pasture from late February to May because this is its most active period of growth. Pasture growth responses to nitrogen can exceed 20 kg DM/kgN and the response can last up to 12 weeks from a single application. This can quickly lead to pasture quality problems if conditions are favourable for pasture growth, resulting in more mulching being required and increasing management costs.
This nitrogen response is sensitive to soil temperature, it’s generally considered safe to apply nitrogen from late May once soil temperatures drop below 12-15oC, Nitrogen should be applied to mulched and oversown areas at 20 to 30kgN/ha once soil temperatures have dropped to help ryegrass seedlings establish.
Can I make kikuyu silage instead of mulching or mowing?
Kikuyu declines in quality as it accumulates more dry matter. Keeping kikuyu in a leafy growing state to maximise quality is more important than managing it for extra dry matter. It’s possible to harvest kikuyu pasture while it’s still short (less than 4.5 leaves) and before the stolon mat has started to build at the base of the pasture. Even harvesting kikuyu when it is short generally makes poor quality silage (8-10 MJME/kgDM) – identify the bales with paint and use them for dry cows in winter.
Therefore, while you can make silage from kikuyu it is not an alternative to mulching or some form of management to remove the trash. Heavy grazing, mulching or mowing back to 5cm stubble leaving the pasture free of trash is still critical for quality silage.
Should I make kikuyu silage in Autumn?
A survey of silage quality on Northland dairy farms (1982) found while autumn-cut kikuyu had adequate mineral concentration, the low level of soluble sugar in the pasture would not likely produce a well-preserved silage capable of high animal performance.
Therefore, Kikuyu can be cut for silage to manage excess growth in the autumn but due to only being a medium quality (8-10 MJ/kgDM) silage it would need to be conserved cheaply and have a worthwhile usage in the farm system.
- Sodium supplement may be necessary where kikuyu silage is a large component of the diet.
- The low Water Soluble Carbohydrate content (WSC), low DM content and intermediate buffering capacity means that it is important kikuyu grass is wilted or silage additives are used reduce risk of a poor fermentation.
How to make kikuyu silage?
- Heavy graze, mulch or mow back to 5cm stubble leaving the pasture free of trash for a quick, even regrowth. It is critical to remove any trash or rank material that may contaminate the silage and affect digestibility and silage fermentation.
- Length of closure: The best quality silage is made from young, leafy growth 25-30cm high, depending on growth rates this may be approximately 20-30 days after closure. Delaying to beyond the recommended regrowth height will reduce energy and protein levels, further if the kikuyu becomes rank and fibrous it may be difficult to compact.
The effect of growth stage of kikuyu on silage quality and potential yield, adapted from TopFodder Successful Silage Guide 2004 Dairy Australia
Potential Yield (t DM/ha)
Vegetative leafy kikuyu
9 - 10
15 - 20
2.0 - 3.5
8 - 9
11 - 15
2.5 - 5.0
6 - 8
6 - 10
3.0 - 8.0
- Wilting requirement: Kikuyu’s water-soluble carbohydrate content is well below the desired level of 2.5-3.0% in the fresh forage. Therefore, rapid wilt is suggested for successful preservation. Aim for 35-40% DM for chopped bulk silage, 35-50% for baled silage. If rapid wilt is not possible a silage additive may be required.
The information is based off the Australian research printed in the TopFodder Successful Silage Guide 2004 Dairy Australia.
Do I mulch or mow?
A mulcher is an important tool on kikuyu dominant farms in mid-late autumn when annual ryegrass or any other seed is being drilled into kikuyu. At this time kikuyu needs to be mulched close to ground level so the ryegrass seed can establish.
Kikuyu grows horizontally and the vertical cutting action from mulching does more damage to stolons than the horizontal action of a mower. Getting close to ground level causes kikuyu to draw on root reserves- during the autumn period when growth is slowing (due to cooler temperatures) this weakens its competitive advantage and the ability for kikuyu to winter.
Mulching also causes kikuyu trash to rot more quickly due to the fine cutting, allowing a more suitable environment for ryegrass establishment.
For the rest of the year a mower can control kikuyu. Mowers are faster and require less horse power than mulchers. A mower is useful for managing high residuals to maintain quality and prevent a kikuyu mat building up in the base of the pasture over the summer.
If kikuyu has been allowed to get out of control (i.e. a mat develops) then a mulcher has the advantage over mowing as it will chop up kikuyu so it will break down more rapidly than the long lengths left behind after mowing. In January, it’s important to start minimising the trash on paddock through mowing, mulching and/or hard grazing ready for mulching and oversowing in the autumn.
How do I set up a mulcher? Optimum height?
The optimum height for mulching is to ground level (0.5-2cm) depending on what your mulcher will allow. Mulching low is important for reducing competition by restricting the regrowth of kikuyu. However, it has been reported that mulching too low to the ground (and scalping) can damage the blades and puts strain on the bearings.
A mulcher has around 20 offset blades mounted on a horizontally rotating drum. Individual blades swing and cut vertically. Using the hydraulic top link and adjusting the height of the skids means to many mulchers can be set up so the blade cuts close to ground level or a close to the ground as your mulcher will allow.
After mulching a short distance, the mulching height should be checked. If the desired level is still not achieved then new holes in the skids will need to be drilled until the skids are lowered to achieve the desired height. A rear stabilising bar is a disadvantage because it collects trash.
Caution with scalping needs to be considered with mulchers that have skids. There are a number of factors that will change cutting height for example:
- After rain mulcher skids will sink more into the soil than on hard ground.
- If the mulcher was set to cut low in dry conditions it may cut too low when the soil is wet and if set low for wet conditions, will cut too high in dry conditions.
- A solid mat of kikuyu will cause the mulcher to cut higher as the skids ride over the mat.
- Mulching to ground level is not recommended on sand because the topsoil is so thin. (Drilling and mowing works well. Neither is spraying roundup on sandy soils recommended, other than for eradication, for the same reason). Kikuyu is more aggressive and harder to manage on heavy clays, with volcanic soils less difficult, and sandy soils easier.
What to sow into mulched kikuyu in autumn?
In most instances use a Hybrid or Italian ryegrass seed. These are winter active and fast establishing to replace Kikuyu in the winter but will also survive into the second summer to carry-over into the following winter.
- Hybrids and Italian ryegrasses grow further into early summer than annual ryegrass cultivars, this provides time for kikuyu to recover and minimises a December feed shortage.
- Up to 50% of the Hybrid/Italian ryegrass plants can be present in the second summer so the undersowing may be carried out on a 2-year rotation to minimise cost (half of the kikuyu paddocks undersown each year)
- Use short rotation annuals in the autumn when paddocks are to be resprayed in the following spring as part of a crop rotation.
- Use short rotation annuals on farms where conditions are more favourable for kikuyu dominance, e.g. warmer areas north of Kaitaia.
- Use the Cultivar Selector Tool to determine the best ranking cultivars and determines season DM production
When to sow into mulched kikuyu?
The optimal time to start sowing ryegrass into Kikuyu is when the minimum air temperature has fallen below 15°C. The soil is still warm enough to get good establishment of ryegrass but close enough to the onset of colder weather to restrict competition from Kikuyu. In general term’s this is the month of April.
Earlier sowings may require more aggressive management to help suppress the growth of Kikuyu. Remove trash if any (areas of kikuyu build-up should have been mown in January to avoid this). Later sowings may suit areas which are frost free and the kikuyu tends to grow and dominate further into the early winter.
If kikuyu continues to grow rapidly after mulching and undersowing and threatens establishment of the ryegrass, lightly graze the pasture for 2-3 hours /day every 7-10 days after undersowing. Grazing to soon after sowing may reduce the seedling ryegrass population by 10-20%, but shading can kill the majority of them. If excessive kikuyu regrowth isn’t a threat, plan to:
- Graze only when the new seedlings survive the “pluck test”
- Apply N on these paddocks after first grazing at 25-30kgN/ha
- It’s important to achieve good residuals in these paddocks through late autumn or early winter – don’t undo the good work with mulching and sowing with poor grazing management.
Should I spray with glyphosate?
It is possible for there to be a residue effect from sprayed kikuyu on the germination of ryegrass when glyphosate is used a high rate (6 litres/ha) especially where there is trash. Where these rates of glyphosate are used, sowing should be delayed 10-14 days. Where you are trying to remove kikuyu from the paddock a cropping cycle is necessary with glyphosate. An autumn spray with glyphosate is more effective at removing kikuyu than a spring spray (when kikuyu may not be present in the pasture)
Chemical topping kikuyu with glyphosate has had variable results depending on application rate and weather. This uncertainty in the outcome means it’s not widely used or recommended in New Zealand.
Glyphosate is not required when Italian ryegrass is undersown and mulched into existing pasture. This strategy boosts winter and spring pasture growth but also allows kikuyu to emerge in summer, reducing exposure to dry summers
Do I need to sow white clover?
Yes, sow clover with your ryegrass cultivars in Autumn. White clover increases pasture growth, quality, and fixes nitrogen, especially in the July to January period. A well-managed kikuyu pasture has a good content of white clover. Remember to treat your new clover well:
- A balanced fertiliser input,
- Avoid shading by grasses,
- Sow at a shallow depth,
- Use a maximum of 15kg/ha ryegrass seed,
- Restrict nitrogen to a minimum,
- Avoid or reduce pugging damage in winter-early spring when clover stolon growth happening,
- Use white clover cultivars with some tolerance to nematodes.
What is the water use efficiency of Kikuyu?
The water use efficiency of kikuyu is similar to maize.
Water use efficiency is twice as high in summer and autumn as annual and perennial ryegrass even when ryegrass is adequately watered. This effect is also due to kikuyu’s greater tolerance of high temperature.
Ryegrass growth rates and pasture quality will both decline as summer temperatures rise where kikuyu’s growth will increase and under good management pasture quality retained.
Table 2: Water use efficiency (MJME/mm water) for Kikuyu in Summer in Comparison to perennial ryegrass in summer and winter