Planning and Establishment

How much pasture should be renewed?

This depends on how long pastures generally last on your farm. If your pastures normally need replacing every 10 years, you would need to replace 10% of the farm each year to maintain a 10 year rotation. Farmers expecting very high farm production and in areas where pasture persistence is more difficult, may need to replace more than 10% (eg. 15%). Research suggests 10% is a minimum needed to keep ahead of productivity decline over time.

Achieving a renewal rate of 10% may seem hard, especially on farms with high stocking rates and few periods of feed surplus each year (eg. some dairy farms). Many North Island dairy farms plant 5% of the farm in summer green-feed crops, so to achieve 10% also requires some grass-to-grass establishment. This can be done by spraying and drilling (direct-drilling), normally done in autumn.

Multi-crop establishment programmes can be used to reduce the impact of paddocks being out of grazing, where overlapping crops generate more feed than is lost during their establishment. For example, spray-drill annual ryegrass in autumn, followed by chicory in October, then new pasture in following autumn. In the South Island, farmers can spread their spray-drilling by doing some in late spring and early autumn.

Farmers may also choose to under-sow pastures (drill seed without spraying old pasture) as part of their renewal programme because there is no loss of production during establishment. This decreases the success of establishing perennial pastures, but is a useful tool to establish Italian or hybrid ryegrasses to boost pasture growth for a period before full renewal after cultivation or by spray-drilling. The overlap of these two methods also compensates for feed lost from spray-drilling.

How much feed is required to replace paddocks under renewal?

This depends on the method you use and its success. Spring spray-drilling irrigated ryegrass pastures in Canterbury can result in only one missed grazing, so only about 1500 kg DM/ha lost production. In many cases extra feed isn’t needed if pasture renewal is timed over the period when pasture growth on the farm exceeds animal demand.

At the other extreme, a dryland pasture may be sprayed in spring, planted in autumn and not grazed until winter, with up to eight months out of grazing. The old pasture may have been able to grow
4-6000 kg DM/ha in that period, but whether extra feed is needed depends on stocking rates and pasture growth on the rest of the farm.

Waikato dairy farms typically spray-drill new pastures in autumn (March) after insect pressure and drought stress has declined. This may also cause 1-2 grazings to be missed compared with doing no pasture renewal. In a strong growing autumn you might not need extra feed. In other autumns, the feed lost can be covered with maize silage or continued grazing of chicory crops planted the previous spring.

What return on investment can be expected?

This will vary as there are many different situations. If old pastures need replacing, and the renewal is successful, very worthwhile returns are made. Some farmers have achieved a return on investment of over 30%. Use our calculators to estimate your return.

How do I prevent insects affecting pasture establishment?

Paddocks selected for renewal usually have a low percentage of productive species - ryegrass, clover - which is often caused by insects that may still be present during the establishment of new pastures, especially when going from old grass to new. It’s important to assess current or predicted insect populations before ordering seed.

A convenient way to control many insects is to order treated seed. Various products protect new plants for about six weeks after planting from insects like Argentine stem weevil adults, black beetle adults and grass grub larvae. Granular insecticide can also be drilled with seed.

Grasses should have an appropriate endophyte to protect from insects that may still be present after the seed treatment or insecticide protection has finished. Slugs and snails can devastate spray-drilled and undersown pastures. If there are slugs, use slug bait and monitor to check the numbers have been reduced. 

Endophyte – what are the key factors to consider?

Standard endophyte (also called HE) doesn’t offer any persistence benefits over some novel endophytes, and it has been shown to reduce performance of animals, which most novel endophytes do not. Some seed of old varieties, like Nui, don’t have any endophyte at all, so their persistence will be very poor in most regions.

Managing and maintaining pasture

What’s required to manage a new pasture for the first year?

Four to eight weeks after sowing, before the first full grazing, is the best time to spray the weeds in new pasture. At this time weeds are still small and there is about 70% or more ground cover.

If fertiliser wasn’t used at sowing, apply this to young pasture. During the first 8 weeks, monitor for insects and weeds. Spray these weeds at an early stage. Three to six months after sowing, carefully rotationally graze when ryegrass has reached 10-15 cm and soil is not wet, leaving a 5-7 cm residual, and spell until it has regained this height.

Six to 12 months after sowing, continue to graze carefully and regularly, apply fertiliser (nitrogen is the main requirement, followed by phosphate, sulphur and potassium) to maintain vigorous growth, and spell in summer if the soil becomes too dry for active growth.

Chemical management of weeds – what needs to be done?

Uncontrolled seedling weeds in new pasture will affect the pasture composition as they vigorously compete for nutrients, moisture, light and space. Uncontrolled weeds will reduce the density of sown species, affecting the production and persistence of the pasture. Early removal (4-8 weeks after sowing and before first grazing) of these weeds allows for more rapid and even establishment and improved productivity from your pasture.

Ensure you use an herbicide that won’t harm clover or herbs in the pasture mix and that will control the weeds. Only one herbicide (Preside) is registered for pastures sown with chicory, but if applied when weeds are very small it controls or suppresses a wide range of weeds. No herbicide is registered for plantain, so some farmers plant new pasture without plantain seed and over-sow with it after weeds have been sprayed. If unsure of timing, chemical type and rates, consult your seed retailer or chemical representative.

How to manage Old vs. New pasture?

New pastures should be considered babies for their first year - all management decisions should be based on what is best for the pasture to develop. Graze only when soils are firm and unlikely to suffer treading damage, graze pastures quickly and leave a reasonable residual behind for re-growth. Stop grazing if the pasture comes under moisture stress. Control weeds early (4-8 weeks) and ensure that enough fertiliser is applied is applied to generate fast re-growth.

Don’t conserve new pastures as either hay or silage for the first 18 months after sowing, especially in the first spring. Older pasture can be used to carry stock when conditions are not ideally suited to grazing new pastures. They can afford to be sacrificed more as they may be close to scheduled renewal anyway.

Pasture persistence

Why don’t pastures persist?

There are several reasons why pastures get damaged and deteriorate over time. These vary between regions and farms, but they also vary from one paddock to another and from one year to the next. It’s also important to remember that it’s natural for pastures to decline over time. Just as an engine in a car wears out, there are continual stresses placed on pastures through grazing or climatic events that lead to a replacement of productive species with those that are less productive. In some cases, the soil health also declines due to a reduction in soil fertility or aeration.

This question has been hotly debated in some regions. Summer droughts have been a major problem, with many ryegrass and clover plants dying from moisture stress and overgrazing - a normal consequence of dry seasons. Insects like black beetle and root aphid have also become more of a problem and can ruin pastures on their own, but the combination with drought has magnified damage. Other significant insects are Argentine stem weevil, grass grub, and porina.

Other causes include pugging and inadequate fertiliser applications, and frequent and close grazing during droughts. 

Are older varieties more persistent than new ones?

No. There is strong evidence that some modern varieties are as persistent as old ones, so there is no need to try to revert back to these. One of the main reasons some old pastures have persisted well is that the standard endophyte they had provides more tolerance to some insects than some novel endophytes commonly used. However, there are now novel endophytes available that provide the same or better tolerance to insects to standard endophyte.

Some varieties of ryegrass can be less persistent than others, especially under regular droughts, over grazing, or treading damage. Some new varieties have strengths in some features (eg. palatability, quality, growth, heading dates), but need good climates and management to persist well. Choose ryegrass varieties with good persistence characteristics, as they differ in their tiller density and resistance to grazing and ryegrass pulling.

Accurate information on relative persistence of varieties is difficult to collect, so ask other farmers in your district and your seed retailer about which varieties have been doing well. Some varieties are designed for specific farm types, so make sure you choose the right one for your situation.

Common terms explained

Direct-drill(ing) See spray-drilling
Endophyte A fungus that lives within a plant (eg ryegrass)
Hybrid ryegrass Ryegrass crossed with another species (eg Italian X perennial)
Novel endophyte A selected endophyte that has been inoculated or bred into a plant
Overgrazing Repeatedly grazing pastures very close to ground and not allowing adequate recovery between grazing events
Pasture renewal Replacing old pasture with new seeds following spraying and/or cultivation
Soil health Factors in soil other than nutrient levels that can influence pasture growth (eg drainage, aeration, organic matter)
Spray-drill(ing) Drill(ing) seed into pasture after spraying
Standard endophyte (aka high endophyte, “HE”, wild-type) The endophyte naturally found in a plant
Treated seed Seed treated with a variety of agents to protect seedlings from insects and/or disease
Undersow(ing) Drill(ing) seed into pasture without spraying