Fertiliser and farming
Compost may be all the rage in city organic gardens, but does it have a role to play in improving pasture production?
An MLA-funded producer demonstration site in the northern tablelands of NSW set out to investigate the effects of compost compared to superphosphate or other on-farm fertilisers.
Although the three-year trials found that superphosphate has a greater short-term impact on pasture production, compost was demonstrated to give modest pasture responses with its effectiveness appearing to increase over time.
The project had two components – a plot experiment and on-farm applications in the paddock.
Compost and superphosphate under control
A replicated plot experiment was established to determine the effects of different rates of compost and super phosphate on pasture production when compared to an untreated control.
Compost was applied at the annual rate of 250, 500 or 1,000 kg/ha (fresh weight). Single superphosphate was applied at the annual rate of 130, 260 and 520 kg/ha (fresh weight). The annual cost of each rate was the same at $46, $93 and $185/ha.
Pasture growth did not respond to either treatment or rate until after the second application when annual herbage production was greatest for plots fertilised with super phosphate. Over the duration of the project there was a strong trend for highest production from plots fertilised with super phosphate at the rate of 260 kg/ha.
The most effective annual rate of compost was 500 kg/ha which increased pasture production by 20% with effects increasing over time. In contrast the most effective rate of superphosphate was 260 kg/ha which increased pasture production by nearly 50%.
Given these treatments had the same annual cost, these effects amounted to extra pasture being grown at the cost of $130 and $51 per tonne for compost and superphosphate respectively.
It is expected that the cost of producing extra pasture will reduce over time as capital application rates revert to lower maintenance rates with little effect on pasture production.
Compost performance in the paddock
The second component of the project was to compare the effect of annual application of 500 kg/ha compost to farm fertiliser practice on 15 paddocks located on four properties.
Eight of the paddocks had compost applied and of the remaining seven paddocks application varied from none to annual and included superphosphate, cow manure, liquid nitrogen, urea and gibberillic acid.
Soil chemical fertility was close to or exceeding ideal values for phosphorus and sulphur which are typically first and second limiting nutrients. The change in soil fertility over the two years of different treatment applications was highly variable among paddocks and not associated with treatment.
Annual stocking rates (17 DSE/ha) and pasture growth rates (20 kg DM/ha/day) on paddocks were high compared to regional averages (8-10 DSE/ha; 10-15 kg DM/ha/day). Compost increased these by 0.4 DSE/ha (2%) and 1.4 kg DM/ha/d (7%).
Towards the end of this trial, pasture responses to compost applications at the plots appeared to be increasing posing the question of a delayed response to treatment. The core issue is the smaller and possibly delayed effect of compost on pasture growth needs to be compensated by an increasing effect over time or a reduction in cost.
These issues will be addressed in the next phase of the project, which is being extended for a further two years.
Download the full report on the compost PDS
Source: Argentine Beef Packers S.A.