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Sheep Response to Agrowplow at Yass

W.M. Wheatly

Agricultural Consultant, Yass, NSW 2582

Soil aeration work that I have carried out in the Yass area since 1981 has demonstrated that dramatic changes can be made to soil, pasture and sheep production. There is little doubt in my mind that the results question the dogmatic approach of those people suggesting that heavy applications of lime are the only way of increasing production on high aluminium acidic soils.

In two large scale grazing trials that commenced in spring 1983, merino weaners are now responding to soil aeration on soils with a high aluminium level.


Over the last ten to fifteen years, subclover-based pastures in particular have been noticeably producing less and less. Even on high fertility situations where fertiliser applications have been maintained, the problem has remained. The reasons for this phenomenon are not clear. Soil chemists have tended to point to an increase in soil acidity, particularly aluminium saturations. They have recommended the widespread use of lime, incorporated into the soil, as the only way of rejuvenating productivity. This expensive operation has unfortunately resulted in extremely variable results.

Apart from any possible chemical problems with the soil, there also appear to be some physical problems. Water infiltration and water- holding capacity of the soil have been variable. Throughout much of the district the soil appears to have poor moisture retention, particularly in autumn when it is needed most. This has resulted in “stop-start” pasture production at a critical time of the year.

Early Trial Work

I have conducted many trials using an Agrowplow since 1961. One of the earliest, but as it eventuated, most valuable, trials was on a pipe-clay soil at W. Painting, “Deepwater”, Bookham.


  • sown to phalaris, perennial ryegrass and subclover in 1969;
  • long fertiliser history over 25 years. Approximately 3500 kg/ha superphosphate;
  • soil test revealed pH at 4.1, phosphorus (Bray) only 10 ppm, but 0-15cm aluminium level at 30%.

Results: (a) Within b months of treating an area to 16cm with an Agrowplow, pasture production was increased approximately 800%.

(a) Dramatic changes in protein, phosphorus, potassium and manganese levels in pasture tissue.

(b) A five-fold increase in total water content in top 15cm.

(c) Increase in plant root growth from 7cm to 14-20cm despite the high soil aluminium level.

(d) Merino hoggets showed a definite grazing preference for areas treated with an Agrowplow.

(e) Treated areas remained green for an additional 2 weeks into summer.

(f) Soil in the areas treated the previous spring had changed to being noticeably more friable.

(g) The areas treated with an Agrowplow have continued to yield considerably more pasture growth every year since autumn 1982.

Grazing Trials

As agronomic responses continued throughout the district over the years, it was a natural follow-on to measure livestock performances.

Two large scale grazing trials were established by the Bookham Agricultural Bureau, which funded the project together with the Board of Adult Education.

Paddocks were measured with a landwheel, accurately graphed, and then sub-divided into two equal areas. One half was aerated, the other left undisturbed.

An Agrowplow was used in each trial as it represented nearly every soil aeration machine in the district.

Details of Project


C.Schlunke, Bowning

I. Bush, Bookham

Total area

19.6 ha

18.4 ha

Area agrowplowed

9.6 ha

9.2 ha

Fertilizer history (super)

4000 kg/na

500 kg/ha


5.10.63 to 16cm

11.11.63 to 14cm

Soil type

grey granite

grey granite

Tractor used

Chamberlain Cb7O

Ford 4000

Engine hp

70 hp

57 hp


9 shank utility with coulters/3 P.L.

7 shank utility with coulters/3 PL.

Diesel fuel used

6.6 L/ha

5.5 L/ha

Fuel cost @ 42c /L




Soil and plant analyses are carried out by Quantum Laboratories, Brisbane. Wool objective measurements are done by the Australian Wool Testing Authority Ltd, Sydney. Wool mineral analyses are done by Clinical Assays Pty Ltd, Sydney.

Trial I - C. Schlunke, “Hill grove”, Bowning.

(a) subcover-based pasture
(b) soil test information

pH 4.5 (1:5 water)
phosphorus 52 ppm (bicarbonate)
potassium 60 ppm
aluminium 22.5% C.E.C or 32 ppm

3075 180 merino wethers (90 each treatment). Dropped spring 1983

Table 1. Sheep Bodyweights (kg) (average of 90 sheep each side) as affected by agrowplowing

Date weighed



Real Difference

















Table 2. Pasture growth (dry matter kg/ha)

Date cut









It is interesting to note that the sheep on the agrowplowed area are eating all of the feed that is produced. However, on the control area quite a reserve of green feed exists.

Table 3. Results of pasture tissue test (19.3.84 only date results available). Apart from sodium and molybdenum, all other minerals were basically the same in each area.




total phosphorus %



total nitrogen %



total potassium %



total sodium ppm



total Mo ppm



aluminium ppm



Despite this, sheep on the agrowplowed area increased bodyweight by an extra 324 in the same period. Even though there was more green feed on the aerated area, both groups of sheep had an abundance of green feed over the summer.

Wool quality

Differences in wool quality began to emerge. Sheep on the control area developed a distinct black tip, whereas on the agrowplowed area this did not happen. instead, black tip sheep on the aerated area began to gradually lose their black tip.

A midside sample of wool was collected on 23.6.84 from 60 sheep (30 each side) and sent for objective measurement.

Average measurements are given in Table 4.

Table 4. Fibre diameter and yield of wool from experimental sheep


Control sheep

Agrowplow sheep

Fibre Diameter (μ)



Wool Yield (%)



I can offer no explanation for an increase in yield of 1.9% between 22.12.83 and 23.6.84. Normally, when a sheep eats more and does better, the wool usually has a higher grease content (lower yield). In this case, the exact opposite has happened so far. The sheep are eating more, doing better, but have less grease in the wool.

Wool Mineral Content

As so many differences were occurring, it was decided to examine the mineral content of the wool. There is a strong school of thought that in human beings, blood samples only show mineral levels at the time of sampling, whereas hair analysis provides a history of mineral levels, The violent fluctuations that take place in blood mineral level do not appear to take place in hair.

The analysis has again posed more questions than answers.

Generally speaking, there is a higher mineral content in the wool from the agrowplowed area. So much so that they could represent two different mobs of sheep from opposite ends of the State.

Although there was a significant difference in the level of most minerals, the interesting ones include:




nearly double on aerated side



slightly higher on aerated side



half as much again on aerated side



two to three times higher on aerated side



three times nigher on aerated side



no change



double on aerated side



higher on aerated side



3075 higher on aerated side



higher on aerated side

Animal Health

There is a marked improvement in animal health in sheep grazing on the agrowplowed area. Sheep in the control area are scouring more, particularly when put under pressure (e.g. mustering and yarding). This had previously been noticed in other sheep in the district, but dismissed because they were not run under trial conditions.

The improved animal health is most likely linked with the increase in bodyweights.

Shearing/Wool Weight

Shearing will be carried out in late July/early August. All wool weights will be recorded. A wool valuer will be on hand to value wool from both groups. Livestock values will also be placed on each group off shears.

Trial 2 - I. Bush, “Old Bogolara”, Bookham

(a) subclover-based pasture

(b) soil test information:

pH 5.4 (1:5 water)
phosphorus 7 ppm (bicarbonate)
potassium 105 ppm
aluminium 20.475 C.E.C. or 41 ppm

(c) 150 merino wethers (75 each treatment). Dropped late spring 1963. Table 5. Sheep bodyweights (kg) (average of 75 each side)

Shearing was carried out 27.5.84. No wool measurements were taken as I felt the sheep had not been there long enough.

Date weighed




Real Difference
















Table 6. Pasture growth (dry matter kg/ha)

Date cut






Botanical composition also appears unchanged.

Tissue test results not available at time of writing this paper.

Although the management in this trial differs from the C. Schlunke trial, the sheep have been on each area long enough to pose one important question: “Why are we getting a response in sheep bodyweight, when we are not getting a response in pasture growth?”

General Comments/Questions from Grazing Trials

The two trials have now only been running since spring 1983, and it is not possible to draw any “hard and fast” conclusions. It is envisaged that the same sheep will continue on each area for a total of 4 years. More positive conclusions may be possible then. However, some of the early results have been the same as other trials previously conducted, whilst others have opened up new areas of research.

1. Pasture and livestock response can be obtained on some high aluminium acidic soils simply by one pass of a machine to aerate the soil,

2. Sheep often show a definite grazing preference for aerated areas.

3. Why has soil aeration resulted in an average increase of 1.9% in the yield of wool in 6 months? Why are the results opposite to current thinking?

4. Why do the sheep on the aerated area graze as a mob, whilst those on the control area graze like “Brown’s cows”?

5. Why is there an obvious improvement in animal health on the aerated area?

6. Why is the mineral content in the wool so different after aerating the soil?

7. Why has one mob of sheep increased bodyweight as a result of soil aeration when there is no increase in pasture production, and no change in botanical composition?

8. I now do not believe it reasonable to assess success or failure to soil aeration merely by measuring pasture production. It is obviously a lot more complicated.

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