Consultant, Euroa, Vic. 3666
Much interest has been aroused in recent years by the results of trials at the Pastoral and Veterinary Institute, Hamilton, Victoria. These trials have, in part, looked at the response of pastures and animal production to increased rates of fertiliser.
HAMILTON LONG-TERM PHOSPHATE TRIAL
The interest in the High Input systems derives from an experiment established by John Cayley at PVI in 1977. A section of low fertility pasture acquired by PVI was resown to perennial grasses
and clover and plots topdressed with different amounts of superphosphate. The plots were grazed with wethers at set stocking rates.
In 1988, the wethers were replaced with spring lambing ewes and, unlike most grazing trials, the stocking rate was allowed to float so that production per head was maintained at one stocking rate at each fertiliser treatment. There were two additional stocking rate treatments at each fertiliser rate, where the stocking rate was allowed to deviate from the "optimum" stocking rate.
The effect of stocking rate and fertiliser treatments are shown in Table 1.
Table 1. Effect of phosphate fertiliser and stocking rate on sheep production
Average fertiliser applied kg P/ha/yr
Stocking rate 1 3 7 14 21 32
Low Weight (kg) June 1992 46.6 51.6 52.7 54.7 55.3 53
Fleece (kg) 4.4 4.5 5.4 5.4 5.0 5.6
Stocking rate 5.0 6.25 8.75 10.0 11.25 12.5
Medium Weight (kg) June 1992 47.7 47.9 49.8 52.6 52.3 52.2
Fleece (kg) 4.2 4.4 4.7 5.0 4.9 5.0
Stocking rate 7.0* 8.75 12.25 14.0 15.75 17.5
High Weight (kg) June 1992 43.1 43.1 45.1 49.4 48.6 45.6
Fleece (kg) 3.6 4.1 4.1 4.2 4.6 4.2
Stocking rate 9.0* 11.25* 15.75* 18.0 20.25* 22.5*
Saul and Cayley, unpublished data
*ewes requiring supplementary feeding
Sustainable stocking rates at each level of fertiliser are bolded and are defined as those where ewes cut more than 4.0 kg wool/head, supplementary feeding is not normally required, balance between pasture utilisation and pasture sustainability is achieved and fibre diameter remained close to 20 Ám.
The bolded treatments are those considered to be sustainable in terms of animal production. The bolded treatments have similar body weights and fleece weights. The results clearly show that there is an optimum stocking rate for each fertiliser application rate.
The interaction of fertiliser and stocking rate has produced some dramatic effects on pasture composition as shown in Table 2.
The results show:
• onion grass dominance at low phosphorus rates;
• an increase in perennial grasses with increasing phosphorus application rates;
• grass dominance in undergrazed, well fertilised plots.
The bolded treatments in Table 2 are those plots with a good pasture balance and it can be seen that they correspond to those treatments showing optimum animal production.
By combining the animal production data (Table 1) with the pasture composition data (Table 2), Figure 1 illustrates the production achieved in kg wool/ha at treatments which are sustainable in terms of species composition and per animal production.
Figure 1. Wool response to phosphorus
Table 2. Effect of phosphate and stocking rate on pasture composition in spring
Average fertiliser applied kg P/ha/yr
Stocking rate 1 3 7 14 21 32
Low Onion grass % 38 20 9 5 1 0
Clover % 4 19 12 15 29 8
Sown perennial grass % 6 7 30 42 39 41
Medium Onion grass % 34 38 4 0 0 0
Clover % 3 7 16 25 25 33
Sown perennial grass % 21 22 36 31 46 46
High Onion grass % 34 36 14 0 0 0
Clover % 10 8 15 40 30 22
Sown perennial grass % 8 17 35 29 31 20
Saul and Cayley, unpublished data
The results obtained from this trial have challenged the conventional wisdom that has governed fertiliser recommendations over the last 20 years.
This is illustrated by comparing the results from Hamilton with the recommendations derived from pasture cutting trials.
In 1990, the average Olsen P value at the Hamilton site for each phosphorus application rate was as follows:
kgP/ha/yr Olsen P mg/kg
(J. Cayley, unpublished data)
The results of the trial show that profitable production can be obtained from the application of 21 kgP/ha at an Olsen P of 12 mg/kg. This is in marked contrast to the responsiveness predicted by pasture growth models. At normal prevailing stocking rates these models would recommend no fertiliser at an Olsen P of 12 mg/kg.
LIMITATIONS OF PASTURE CUTTING TRIALS
Pasture cutting trials have been traditionally used to predict pasture responses to fertiliser application. Animal responses were then estimated on the assumed utilisation of the feed produced.
There are a number of reasons why animal responses may be under-estimated from cutting trials. They are:
under-estimation of pasture growth rates due to:
not maintaining optimum leaf area index (allowing plots to become rank prior to cutting);
no recycling of nutrients via the animal
under-estimation of quality aspects of feed:
digestibility is improved where pasture is kept short;
improved digestibility where fertiliser applied.
Research has shown that the productivity of many Victorian pastures is well below their potential due in large part to nutrient deficiencies. The research has also shown that increased stocking rates and increased fertiliser applications can be profitable on sheep farms. To date there has been little evaluation of these systems on beef farms.
However, the principles are the same for both beef and sheep farms and if they can be supplied to beef farms then similar levels of productivity should be possible.
The application of fertiliser to responsive pastures will result in a large increase in spring growth.
The critical factor in High Input systems is the utilisation of the spring flush. Control of the spring flush not only results in better quality feed but also higher pasture growth rates.
Control is most easily achieved where grazing pressure increases during the spring due to the reproductive cycle of the stock, i.e. spring lambing ewes > responsive than autumn lambing ewes > responsive than wethers.
APPLICATION OF HAMILTON RESULTS TO OTHER AREAS
There is little debate that most pastures will respond to increased applications of fertiliser. In order for such a course of action to be profitable the feed produced must be efficiently converted into animal product.
Whether this is profitable will depend very much on the individual farm situation. It will depend on:
the responsiveness of the pasture;
the profitability of the enterprise;
the sensitivity of the enterprise to increased feed availability;
and be influenced by:
the farmer's attitude to risk;
the requirements for extra labour;
the demands placed on other aspects of farm management.
THE GRASSLAND'S PRODUCTIVITY PROGRAM
The Grassland's Productivity Program is an initiative of the Grassland Society of Victoria, funded by the Wool Research and Promotion Organisation and supported by the Victorian Department of Agriculture.
The Grassland's Productivity Program was launched in 1993 with the objective of encouraging farmers to critically evaluate high producing productive pasture systems on their own farms.
Under the Program, the facilitators help interested farmers establish paired paddock comparisons on their farms.
One paddock (Control) continues with the normal management practice carried out on the farm. The other paddock (Productivity paddock) receives increased rates of fertiliser based on the results of soil and plant tissue tests and other treatments, such as lime and herbicides, required to improve the pasture.
The objective of the comparisons is to develop or modify existing farm systems to efficiently utilise the extra feed produced and to evaluate the profitability of such systems.
Farmers participating in the project within localities meet regularly to monitor the progress of the comparisons.
The facilitators have worked closely with Department of Agriculture staff in NSW, Victoria, South Australia and Tasmania to establish groups. Assistance has also been forthcoming from a number of agribusiness personnel and consultants.
Twenty-five groups formed
The demand to establish comparisons has exceeded expectations with around 100 farmers in 25 groups conducting paired paddock comparisons.
The rainfall range covered by the comparisons varies from 1000 mm to 450 mm.
A wide range of enterprises and pasture types is being evaluated. Wool sheep make up 66% of the farms, cattle 20% and meat sheep around 15% of the comparison paddocks. Some wethers and steers are being run but most comparisons are breeding enterprises with winter or spring reproducing stock.
Most paddocks contain established perennial grass/clover pastures, although annual pastures are being investigated at a number of locations. Some of these pastures form part of cropping rotations and an aspect of the evaluation will be the carryover effect of the productive pasture system on subsequent crops.
While the dry start to the season has meant few large differences have been observed so far, all groups have met at least once to inspect paddocks in the comparisons.
The profitability of productive pastures depends upon efficiently utilising the extra feed produced. In order to help participants in the Program make objective decisions about adjusting stocking rates, workshops on pasture and stock assessment have been held with all regional groups.
At these workshops, participants are shown how to assess stock condition, pasture availability and pasture composition. These measurements are then developed into a framework to enable decisions to be made about adjusting stocking rates, supplementary feeding.
The GPP aims to have 750 farmers across south-eastern Australia evaluating productive pasture systems by 1996. To achieve this objective, GPP is looking to establish another 25 groups for the 1995 growing season. Additional funding is being sought to enable the appointment of more part-time facilitators to service these groups.