Table of Contents
- Trends in pasture eaten 1990-2014
by David Chapman, DairyNZ
The value of low-cost pasture feeding for the profitability of farm businesses is well known, and applies irrespective of farm system type (system 1 to 5).
On-going profitability and industry competitiveness will require continued gains in pasture productivity. In the near future, we will also come to value pasture options for their ability to help reduce environmental emissions, especially nitrate leaching.
As the expectations of pasture increase, it is timely to look at how much progress we have made in pasture eaten per hectare across the industry, where that progress has come from, and where it might come from in the future.
In 1990, average pasture eaten per hectare across the 1.02 m hectares of dairy land was 8.86 t dry matter (DM). Twenty-five years later, in 2014, this had risen to 11.61 t DM/ha across 1.75 m hectares of dairy land.
On the surface, the increase of 2.75 t DM/ha in that time looks healthy. It amounts to + 110 kg DM/ha per year, or 1.24% per year. But there are some warning signals lurking behind the headline figure when we look at the source of the gains.
Firstly, in the same period 1990-2014, nitrogen fertiliser use in dairying increased by 150 kg N/ha per year. Assuming each kg N applied grows an additional 10 kg DM, and 80% of this is utilised in pasture eaten, over 25 years this adds 1.2 t DM/ha to the national average, or 44% of the + 2.75 t DM pasture eaten / ha change.
Secondly, an additional 570,000 ha has been converted to dairying in the South Island over this period, mostly in Canterbury and Otago (under irrigation) and Southland (with better summer pasture growth potential). Accounting for the difference in pasture growth potential, if that 570,000 ha expansion had occurred in the North Island, explains about 0.5 t DM/ha of the gains since 1990.
Thirdly, increases in the carbon dioxide concentration of the atmosphere over the 25 years is likely to have increased pasture growth by about 5% due to the ‘CO2 fertilisation effect’, accounting for about 0.4 t DM/ha of the change.
These three factors together contribute 2.1 t DM/ha, leaving a ‘residual’ of 0.65 t DM/ha, or a gain of about 26 kg DM/ha per year. This is probably a result of improvements in pasture management, and genetic gains through plant breeding.
If we assume all the gain is from plant breeding (a big assumption!), the 26 kg DM/ha per year gain in pasture eaten is about half of the 50-60 kg DM/ha increase in pasture grown per year of breeding effort (about 0.5% per year) estimated from the DairyNZ Forage Value Index (FVI). Thus, we could speculate that the ‘realised rate of genetic gain’ in pasture dry matter yield (i.e. the gain that farmers are actually capturing) is about half of the potential. This is not unreasonable, given that: re-grassing rates across the industry are ~ 8% of total pasture area per year (so new genetics only slowly make their way into farming systems); and problems with pasture persistence in the upper North Island due to more-severe climate conditions (discussed further below) are probably eroding some of those gains.
Looking back at the source of gains in pasture productivity over the past three years, we can immediately see that two of the three big ticket items (N fertiliser use, and expansion into the South Island) are now more-or-less ‘off the table’ as a result of environmental regulations being implemented to reduce nitrate leaching from dairy farming. The increase in N fertiliser use from 1990-2014 occurred in an un-regulated environment: that is all changing now. If anything, N fertiliser rates used on farm are likely to decline over the next decade.
Which begs the question, where will the gains needed to maintain industry profitability and competitiveness come from in the future?
As noted above, the FVI predicts that ryegrass breeding is delivering about 50-60 kg DM/ha per year of breeding effort. By comparison, we can estimate that a farm stocked at about 3 cows/ha and routinely using improved animal genetics will need to utilise (not just grow) an additional 40 kg DM/ha per year to meet the increased intake capacity of the higher producing cows to maintain that stocking rate.
Thus, plant genetic gain could keep pace with animal genetic gain – if the potential of plant gains is realised on farm (the calculations above suggest it is not), and stocking rate is not increased (which is not the case – stocking rates have increased across the industry from 1990-2014). The pressure is on.
So, what do we know about current rates of gain in ryegrass, and potential for future gains?
The main trends in ryegrass breeding over past 30-40 years have been diversification into later heading cultivars (facilitated by use of genetic material from NW Spain), development of tetraploids, and release of novel endophyte strains, with some movement on the margins into high sugar grasses and ryegrass x fescue hybrids.
Based on the past 7-8 years of research carried out to support the FVI, the outcome of this breeding work seems to be:
- Later heading has delivered the most value in DM production – it has spread the seasonal growth curve into the shoulders of the season where additional DM grown has high economic value, with essentially no change in spring production (so ‘evening-out’ the growth curve somewhat).
- Compared with mid-heading cultivars, later-heading types also have:
- lower intensity of flowering (fewer tillers go reproductive) – this is positive for feed quality; but
- less clover in the total DM – this is negative for feed quality.
- There have also been gains in pasture feed quality. Late heading diploids generally exceed mid-season heading diploids by ~ 0.1 MJ ME/kg DM. In a milk production experiment conducted in the Waikato by DairyNZ, this translated to ~ + 12 kg MS/ha per lactation. Assuming a milk price of $6/kg MS, and no extra costs, this is a net increase in profit of $72/ha/year.
- Tetraploid cultivars typically exceed mid-season diploids by about 0.3 MJ ME/kg DM, worth ~ $10/ha/year of breeding effort – but with a risk of poorer pasture persistence compared with diploids.
In the upper North Island, it is very clear that on certain soil types (especially light texture ash soils, and peats), possibly exacerbated by the cropping/cultivation history of those soils, newly-sown perennial ryegrass pastures are unable to persist beyond three years, and are often gone after two years.
We estimate that, in this region, 30,000 – 50,000 hectares of dairy land (about 10% of the total dairy area) previously in ‘perennial’ pasture has moved to annual pasture/crop since 2007/08. There are big question marks over the environmental sustainability of this amount of cropping and re-grassing, let alone the financial sustainability of carrying the associated costs each year.
Many of the farmers we are engaging with in the region over this problem are now implementing a ‘no cropping’ or ‘no soil disturbance’ policy in an attempt to stem the tide of soil degradation.
On the vulnerable soils in this region, it seems that the environment is dominating, and overpowering the coping mechanisms of perennial ryegrass. Hotter, drier summers, lasting for longer (consistent with climate change projections), combined with increasing insect presence and damage under continuing heavy grazing pressure (high stocking rates, fast rounds) results in lethal plant stress levels.
Ryegrass genetics per se is not the cause of the problem. In studies where we have re-sown new cultivars and the old Nui ryegrass type (with standard endophyte) at the same time, into the same soil, we have seen no difference between them in pasture survival.
The old ‘wild type’ endophyte and the newer endophyte strains are powerless to protect ryegrass plants from the most-severe climate and soil disturbance pressure. We also know that sowing rate is irrelevant, and that reducing grazing pressure and/or standing cows off during summer cannot solve the problem if the other factors above are present.
Taken together, these findings suggest we may need to change the paradigm, and change our expectations of ryegrass pastures, if we want to keep productive ryegrass pastures for longer in these situations. It may be necessary to ‘take the foot off the pedal’ when growth conditions are favourable for plants, e.g. in spring, to allow them to exploit those conditions and build their resilience so they can cope with the harsher conditions ahead.
For example, in a study currently underway at DairyNZ Scott Farm, Newstead, we are comparing the effects of a ‘long spring rotation’ (designed to allow plants to build root and tiller populations before going into summer) and full grazing deferral from mid-spring to late summer (designed to return hundreds of kilograms of seed and fill pasture gaps with new ryegrass plants) on pasture persistence and production.
DairyNZ is either leading, or investing in, research and development projects aimed at lifting pasture performance – in DM yield, quality and persistence, as well as for the mitigation of environmental impacts. Some examples of these projects are presented below. More information can be found at www.dairynz.co.nz/feed/
“There is no heavier burden than an unfulfilled potential.” Charles Schulz
Often it can be hard to take action if we don’t have a good feel for the target that we should be aiming at. In the case of pasture eaten, we have a reasonably good picture of the range being achieved on farms from DairyBase. This information has now been pulled through into a simple on-line app called the ‘Pasture Potential Tool’ which can be found at: www.dairynz.co.nz/pasture-gap/
By entering your farm location, the tool will display pasture and crop eaten data for farms within a 20, 40 or 60 km radius for the specified year, and suggest a benchmark potential figure equivalent to the top 25% of farms in the area, as shown in Figure 1.
In this case, the DairyBase data indicate the potential is at least 13 t DM/ha per year, based on the population of farms (31 in this example) within a 60 km radius.
If your farm’s current pasture and crop eaten is less than the benchmark, the gap analysis tool in the ‘Pasture Potential Tool’ provides pointers on factors which might be holding production back. This is a good place from which to start realising any un-tapped potential in your greatest financial asset: land.
The Forage Value Index is a strategic initiative that allows us to put dollar values on forage plant traits, estimate how much gain is being achieved in those traits, identify the ones that are most valuable to farmers, and put support behind projects that will accelerate gain in the important traits. This is the ‘long game’ strategy behind the FVI. In the meantime, it can help you to sift through the long list of commercial ryegrass cultivars and endophytes to find the combinations that should work best in your region.
Related to the genetic gain goal in the FVI noted above, there are three new options DairyNZ is supporting under development, in NZ and overseas, for creating and selecting better plants faster.
- Genomic selection (GS)
Already being applied in animal breeding, genomic selection should help accelerate genetic gain in forages by reducing the time required to develop a new cultivar (from around 14 years currently, to perhaps 10 years). It does not create novel variation in ryegrass for breeders to use – rather, it helps them identify the best plants to use in breeding without having to wait 3+ years to identify them from field trials.
NZ breeding companies are now starting to use GS for ryegrass breeding, with clover to follow in the next 2-3 years.
- Hybrid perennial ryegrass breeding
The details are complicated! Suffice to say, this will allow perennial ryegrass breeders to do what maize breeders have done for more than 60 years – exploit hybrid vigour. This hasn’t been possible in perennial ryegrass until now. It is a non-GM method, so can be used now without restriction. Early indications suggest 10+% yield gains are possible – which, if realised, would equate to 20 years of breeding effort using current methods. This would be a welcome step-change.
NZ breeding companies are testing perennial ryegrass hybrids in the field now, and cultivars may be available within 4-5 years.
- Gene-edited, and genetically-modified (GM), ryegrasses
Both of these technologies are presently subject to strict regulation in New Zealand: to the extent that we are unlikely to see commercial products within the next 10-15 years. The best-known example is the ‘high metabolisable energy’ (HME) ryegrass developed by AgResearch. This is a GM product, with significant potential to, among other things, reduce methane emissions from dairy cattle. Currently it is being trialled in the USA, because field testing is not permitted by law in NZ.
In general, there is not enough variation within perennial ryegrass to select for cultivars that will markedly reduce nitrate leaching, or greenhouse gases emissions. The HME example above bucks that trend – because GM creates variation that is not found in the natural ryegrass world.
Hence, attention is being given to other species that can change the game, and in due course the FVI will expand to accommodate these species and their environmental value (expressed in $ terms alongside the $ value of their production traits).
The ‘Forages for Reduced Nitrate Leaching’ programme has identified four plant options that help reduced nitrate leaching:
- The grazing herb, plantain, which (if present at ~ 30% of total pasture DM) dilutes the concentration of N in cattle urine and therefore reduces N leaching from urine patches. It also acts like a ‘biological DCD’ to inhibit rates of nitrate formation in the soil.
- Italian ryegrass as a winter pasture option where it’s high cool-season growth rates result in high N uptake from the soil and reduce the amount of N in the soil at risk of leaching
- Fodder beet, which has a very low crude protein content (< 10% of DM, compared with pasture at 22% +) and therefore results in less surplus N from the diet being excreted in animal urine.
- Catch crops, such as oats or annual ryegrass, that can follow a grazed crop (such as kale) to mop up the N excreted by cattle and reduce the amount of N in the soil that is at risk of leaching.
More work is underway with farmers right now looking at the best ways to fit these options into farm systems. For more information, follow the url below: https://www.dairynz.co.nz/about-us/research/forages-for-reduced-nitrate-leaching/
Poor persistence of newly established pastures erodes the gains possible from better management and genetics. It is like trying to walk up a down-escalator: poor persistence is a force pushing back against progress. There is clear evidence that a big part of this problem is down to the climate getting drier and hotter in the north over the past 15 years.
This may be just climatic variation: or it could be long-term climate change, similar to what has been seen in parts of southern Australia over the last 30 years. Either way, we can’t ignore it. We can’t change the environment very easily. Irrigation is a good example, and there could be scope for increasing irrigable pasture area in the future if pasture-based dairying can retain a comparative advantage relative to other land-based industries, especially high value horticulture.
In the meantime, research and development is exploring:
- Some basic plant knowledge such as: what kills plants in the field? If plants survive but lose yield over time, what causes this, and can we find work-arounds?
- Ryegrass breeding: a longer-term solution where breeding tools like genomic selection could help.
- Soil management, particularly the maintenance of soil structure and organic matter. Using only ‘soil-friendly’ cultivation practices is a big part of this. There is also a strong suspicion that soil-borne pathogen loads and root diseases are playing a big role in plant loss, yet we know virtually nothing about these processes in our soils.
- Grazing management to support better plant survival, or replenish plant populations via re-seeding. We are working on answers to questions such as: what method to implement when and where, at what cost, and with what long-term benefit?.
- Alternative perennial pasture options. There are several (e.g. tall fescue, cocksfoot, lucerne) but past experiences on farm have been mixed. Again, there is a serious lack of systematic information on their potential, management and systems integration, which needs to be addressed.
Expectations for improved forage production are growing – at the very time when two of the major drivers of increased productivity over the past 25 years (increased N fertiliser use and expansion into higher rainfall/irrigated environments) are being corralled by environmental regulation.
As an industry, we will need to capture management opportunities on-farm, and drive technological developments beyond the farm gate, to keep the momentum going. Stagnation in pasture eaten could lead to slow suffocation of the industry by depriving farmers of the ‘oxygen’ that drives profit.
A good place to start for many farmers is to calculate and benchmark current pasture and crop eaten, and deal with factors creating a gap between current and potential performance. Rates of genetic gain in pasture production will increase over the next 5-10 years: they have to if we are to maintain a viable grazing-based industry.
The FVI will allow us to track rates of gain and move resources into the new developments with the highest pay-off for farmers. The scope is now expanding to include plant traits that help meet the environmental limits that farmers are being forced to operate within. There are good forage options available now, and these will expand over the next decade.