Pasture renewal critical to maintaining healthy farms

Often this is taking the worst or most underperforming paddock on the farm and attempting to make them the highest performing. To achieve this, several checks need to be made to get a successful pasture renewal result.

According to Agricom, the most important is to identify the reason for the paddock underperforming to start with:

• Checking the paddock fertility
• Identifying issues of drainage or compaction
• Identifying the weed and weed grass species limiting productivity
• Identifying the insect pests that mostly influence your pasture production and persistence.

Agricom says this process will identify whether you can do a double spray grass-to-grass programme or whether you require a cropping rotation to reach your end goal of a productive persistent pasture.

“Replacing poor producing paddocks with new pasture is one of the simplest ways to invest on farm for a significant and relatively predictable return. The higher your farm’s performance, the more it can gain from intensified pasture renewal. And it isn’t only for ‘high input’ farms - any kind of farm or grazing-based business can benefit from pasture renewal.”

New pasture is much more productive, says Agricom. Most pastures deteriorate from a number of causes - weed invasion, particularly low quality grasses like paspalum and Mercer grass, dry conditions, wet/ flooding, poor fertility, poor drainage, diseases, insects, pugging, soil compaction, overgrazing and poor management.

Over time, the population of desirable, productive plants in a pasture declines, while undesirable or unproductive plants increase and pastures become ‘runout’. Old pastures produce less drymatter, are lower in metabolisable energy (ME) and have reduced stock performance. This decline compounds as the pasture ages.

Successful pasture renewal can increase DM/ ha/year by around 3–6 tonnes. This is true for all farms – the extent to which the extra production can be converted into additional income varies.

According to DairyNZ, renewing pasture is crucial for maintaining healthy dairy farms, and there are four primary methods to consider: cultivation, spray-drilling, undersowing, and oversowing. Each method has its pros and cons, with factors like cost, time, and specific pasture conditions influencing the choice of renewal approach.

DairyNZ advises farmers to choose the method that aligns with their farm’s needs and conditions.

There are four main ways to renew pasture, cultivation, spray-drilling, undersowing and oversowing.

Cultivation

Involves breaking up the soil prior to sowing with the likes of a plough, power harrow, discs or rotocrumbler. It is necessary where there is a need to eliminate compaction or levelling, or lime incorporation is required.

Advantages

• Most consistent results
• Eliminates compaction
• Best pest & weed control
• Can level paddock
• Can incorporate lime
• Allows good soil coverage by seed

Disadvantages

• Most expensive method
• Slower to first grazing (6-10 weeks)
• Softer and more prone to pugging during establishment

Spray and drill

A direct-drill is used to sow treated seed into an uncultivated paddock after existing pasture killed by herbicide.

Advantages

• Herbicide controls competition
• Less expensive and less time consuming than cultivation
• Quicker to first grazing (6 weeks)
• White clover establishment is possible (see below)
• Long term solution

Disadvantages

• Less opportunity to correct pH
• Won't fix soil compaction or level paddock
• May revert to old pasture more quickly than cultivated paddocks
• Two drill passes at half the seeding rate are desirable to achieve dense pasture
• Loss of pasture production after spraying.

White clover establishment (after killing existing pasture)

Drill ryegrass using the main-seed box. Drop white clover seed onto the soil surface from the small-seeds box in front of coulters sowing the ryegrass. Cover seed with a brush or bar harrow.

Undersowing

Use a direct-drill to sow treated seed into existing pasture.

Works very well in the narrow window of time when a pasture has thinned out but has not yet been overtaken by weed ingression.

Use after extended dry conditions where large areas need to be sown, or after winter pugging damage. Results are variable where it’s used in pastures too dense for the new seedlings to establish well.

Advantages

• Cheap and simple
• Allows large areas to be done
• Italian or hybrid can boost winter-early spring growth

Disadvantages

• Doesn't work in dense pastures
• Doesn't control problem weeds
• Not suitable for white clover establishment
• Usually only a temporary fix.

Oversowing

Treated seed is broadcasted on to the surface of the soil.

Generally used to repair smaller areas, for example after pugging damage, or to establish white clover in spring into pastures where the land is too steep or stony for cultivation.

Not recommended for improvement of lowland pastures due to high seeding mortality.

Sowing rates are generally higher, as establishment rates of seed placed on the ground surface are lower.

Advantages

• Can introduce legumes & N fixation
• Can apply with fertiliser

Disadvantages

• Variable results
• Hard to control competition

New pasture is much more productive than older pasture.

What Rate of Renewal?

The correct rate of pasture renewal for a farm varies depending on the state of the pastures, and the goals of the operation.

Barenbrug covers how to assess pasture performance across a farm and plan accordingly.

Rate of renewal

Pasture renewal programmes vary widely across NZ, ranging from 0% to over 30% of the farm area each year. Dairy farm renewal averages about 8% compared to 2-5% on sheep farms. The percentage of a farm renewed also determines how long a pasture must last, for example a 5% rate of renewal means a pasture must last 20 years.

Benefit of renewal

The benefit of new pasture is the gains it will deliver over existing pasture. So it’s important to estimate the current pasture performance versus potential.

Pasture growth varies widely between individual paddocks across every farm. On flat farms there is typically a 100% difference in DM yield between best and worst paddocks. This difference is much higher on hill country properties.

Growth differences between dairy paddocks of 6 t DM/ha are common. This means under-performing paddocks may produce 300 kg MS/ha less than better ones (based on 75% utilisation and 15 kg DM/kg MS conversion).

Measuring paddock performance

Comparing the performance of individual paddocks allows you to quantify the potential gains of pasture renewal on the farm.

The best paddocks show what can be achieved, with the difference between those and the worst illustrating the potential for improvement, provided paddocks share similar topography and soil type.