The correct rate of renewal for a farm varies depending on the state of the pastures, and the goals of the operation. This section covers how to assess pasture performance across a farm and plan accordingly.
Rate of renewal
Pasture renewal programmes vary widely across NZ farms, ranging from 0% to over 30% of the farm area each year. The average on dairy farms is 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 a new pasture is the gains it will deliver over existing pasture. So it's important to estimate the current pasture performance versus potential.
Current pasture growth
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 paddocks on dairy farms of 6t 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). On a sheep and beef farm the poorest paddocks could be carrying 30-50% fewer stock with much slower animal growth rates.
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 are similar (e.g. same topography, soil type etc).
One way to find out how much individual paddocks grow is to record stock grazing days (Table 1). Alternatively you can use a plate meter, pasture cage measurements or visual yield estimates from farm walks to estimate pasture cover to calculate paddock growth. Some software (e.g. Pasture Coach, Agrinet or Minda Land and Feed) does this automatically from weekly pasture cover data.
At the end of the season, grazing days for each paddock can be added up to identify total grazing days. Include other growth such as silage made and also which paddocks supplement was fed in. Where paddocks are different sizes, divide total grazing days by the paddock size, so total grazing days/ha can be compared. In this simple example paddock A is carrying 25% more stock than paddock B, and 33% more stock than C.
Create a paddock profile
This paddock performance data can be used to rank paddocks within their productive group (e.g. different soil type, topography etc). The example in Table 2 is for the Lincoln University Dairy Farm (LUDF), which has three different soils marked by different colours.
The green soil (Templeton silt loam) is the most productive so you compare between paddocks with this soil type. This identifies the potential of other paddocks within this soil type, with N2 producing an estimated 4.7 t DM/ha less.
Just as farmers identify and cull the 'tail end' of their herd or flock to improve animal performance, here the same thing is done with pasture, culling tail end paddocks to lift farm pasture performance.
Low hanging fruit
While the graph above shows the potential gain from renewal, it's also important to look at the cost or difficulty in realising those gains. The best return from investment in pasture renewal is from significant yield gain achieved at a low cost.
For example on the LUDF DM yield gains are typically much easier to achieve on the green (Templeton) soils than the very poorly drained orange soils (Temuka clays), on which gains are often reliant on drainage, which significantly increases costs.
Continuing to assess paddock performance during the following years allows you to evaluate the success of pasture renewal. Typically pasture renewal delivers good gains. If this is not the case, underlying reasons for poor paddock performance probably have not been rectified. Continual evaluation allows farmers to fine-tune renewal techniques to identify what works best, giving the best success for a particular farm system.
Capture benefits of new pasture
New pasture grows more so:
- A higher stocking rate may be needed.
- More fertiliser will be required.
- Change in management systems may be needed.