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What is the potential pasture production and carrying capacity?

There have been some discussions on this topic on Twitter that are better answered in this blog. But for discussions on it, please join me and others on Twitter. My twitter account is @calukafarms. This blog is not setup for banter and discussions.


Hopefully we all know the French & Schultz equation for determining potential wheat yields. We all once considered it impossible to reach because everything cannot be perfect. Today, it is easily surpassed across southern Australia. Efficiency of grain production based on water use is also not just 20kg/ha/mm as French & Schultz concluded. We now know water extracted from deep in the profile after flowering when wheat is moisture stressed is as high as 60kg/ha/mm.


There is a potential pasture production formula based on ryegrass, clover and medic pastures. All C3 species. It’s from CSBP (a fertiliser company in Western Australia) using their decades of research. The formula was published a few decades ago, and though I did not see all the raw data, they did make a very interesting sideline comment that is of great significance.


Their formula is for the potential stocking rate, but imbedded in it is the equation to estimate potential pasture production.


Potential DSE/ha = [{(GSR-50mm) x 28kg/mm/ha} - 500kg/ha] / 365


GSR = growing season rainfall. You can add maybe a third of summer rainfall that is already in the soil to make it a little more real world.


50mm is what they measured as an average loss of moisture in evaporation.


28kg/ha/mm was their suggested maximum potential production. However, three times they did measure 40kg/ha/mm. So because it was achieved and measured, I use 40kg/ha/mm, even though that is still wrong. If it has been achieved, that is not the potential. The potential is always higher than what can be achieved.


500kg/ha was their deduction in pasture production they termed wastage - trodden on, rotted away, defecated on etc. It seems very low but that is what their trials measured.

365 is the assumed kilograms of good quality pasture that is needed in a year to maintain one DSE. ie ~1kg/day/DSE. For those who don’t know, DSE is Dry Sheep Equivalent and assumes it is a wether or a dry (not pregnant) ewe of ~45kg/ha liveweight. A heavier animal or a lighter one that is growing in weight will have a higher DSE rating. See https://www.dpi.nsw.gov.au/agriculture/budgets/livestock/sheep-gross-margins-october-2015/background/dse

If you create a guideline or formula and call it potential based on what the best farmers are doing, it is not a potential. It is fine to say this is what the top 1% of farmers are achieving, but it is erroneous to call it “potential”. Potential is always beyond what someone has achieved.


So, here are some calculations using the CSBP formula and what they consider is the potential.

GSR rainfall (mm)

Potential DSE/ha

Potential pasture production (kg/ha/year)

150

10

4,000

300

26

10,000

450

42

16,000

600

59

22,000

750

75

28,000


Remember this formula is based on actually achieved results, so it is not really the potential even though I have used that word. The actual potential is somewhere north of this. However, I think it is a wake up to us all that we need to be asking of ourselves, why aren’t I achieving this? Is there something I can do to get close to these levels? Is it profitable to do so?


There is something else to be considered here. If you have C4 perennials in your pasture system, then your potential pasture production is even higher again. Kikuyu for example, is a C4 grass. It uses rain outside the “growing season” and grows more biomass per mm of water, and it uses deeper water that C3 species cannot reach. But just as importantly, it produces more than 40kg/ha/mm. I actually don’t know how high it is in kikuyu because I have not found research that has measured it.


You may look at the above table and be no where near those production levels. Keep in mind, the actual potential is higher than this.


I think it is similar to what we went through back in the late 1980’s and 1990’s. French & Schultz published their paper in 1984. I was given a research project to find out how to get wheat yields in the >450mm annual rainfall area on WA along the south coast to the level French and Schultz said we could achieve. There was every reason (excuse) under the sun why no one was reaching anywhere near the theoretical potential. And then we did start reaching and beating it.


I have a newspaper clipping from an interview I gave, where leading farmers said 4t/ha wheat was impossible, even if the year was perfect. It is laughable now of course because it is so easy to achieve 4t/ha, but back then, the thinking was that if it was possible, we’d all be doing it.

To be blunt, everyone was making the same mistakes.


Now that I am in the pasture and livestock industry, it has struck me how far everyone is below what is possible with profits in this industry. We have far more upside than the cropping industry. I think we are on paragraph 2 on page one of a 200 page book on how to be a profitable livestock producer. If you know me, there is a tongue in my cheek with that comment :-). It’s exaggerated, but the point is that we as an industry, are less than a quarter of where we should be in profits. And I do not mean because of low prices for our produce.

I mean that we have so much further to go in genetics and putting that together with pasture agronomy and animal husbandry.


We are in the 700-800 rainfall zone. We can assume 750mm in the above table applies to us. We are kikuyu based and our growing season is March to November. We have some green all summer from the kikuyu, no matter how dry it is. Though our potential DSE is north of 75 DSE/ha, our target is 30 ewes joined per hectare. We aim to lamb twice in 12 months too, not just once, nor three times in 24 months. We have a mini spring and a long spring in our region and we are moving our lambing times to utilise them as much as possible.


We are currently still building our ewe numbers so are not at our goals yet. We are currently in the 35-39 DSE/ha range, but expect to average over 50 DSE/ha when we get to our target ewe levels. We will make mistakes and not get it right for awhile, but I am convinced that one day in the not too distant future, the southern Australia region will have many farmers achieving more than 60% of what the CSBP formula calculates.


Why aren’t people achieving anywhere near this yet? There are many reasons, and some we probably do not know about yet until we get closer to those profit levels. Possible limitations are sub-soil acidity or sodicity, a multitude of nutrition deficiencies (and toxicities for some), husbandry inefficiencies, and poor genetics. Genetics for us is a big one. We have a long way to go to have the sheep we would like.


I have no idea what the most profitable level will be, hence why we are aiming for a conservative target first. If we get there and we can see there is more profit to be had with a higher stocking rate, then we will do that. 30 ewes/ha is just an interim target for us at the moment.


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