A long term farming systems trial was conducted at Condobolin in order to analyse the impacts of current farming systems on soil nutrients and soil carbon. The CWFS Systems Comparison Trial (commenced in 1998) was spread over the 160 ha trial site at Condobolin. The 160 hectare site was further broken down into four main replicate blocks. Each block had four different farming systems on trial.
These farming systems include:
Traditional farming system (CT)
The CT represents a mixed farming system that uses conventional tillage with a pasture phase and grazing.
This system was set up to reflect what many growers in the region were using on their own properties. The crops in rotation on the system included long fallow wheat (LFW), short fallow wheat undersown with a pasture combination (SFWu/s) and a grazed pasture. The sown pasture contained annual medics and lucerne.
Reduced tillage with livestock (RT)
The RT represented another mixed farming system using a rotation of (LFW) long fallow wheat under sown with a pasture combination (LFWu/s), grazed pasture and a period of rest between wheat crops. During the rest period stubble was maintained and weeds were controlled by grazing and herbicide applications (in August). The sown pasture contained annual medics and lucerne.
Zero-till with no livestock (CC)
The CC represented a continuous cropping rotation that was dependent on herbicide application for weed control.
This system was chosen to represent the intensified cropping systems in the Central West (NSW). The crops in rotation were wheat, barley, a pulse crop, SFWaP (aP – after pulse) and a green manure crop (Pulse). Initially the pulse crop was sown as canola and then converted to a pulse. After a number of years the pulse crop was not harvested and the pulse and green manure crops were essentially the same treatment.
Perennial Pasture (PP)
This farming system was divided in 12 equal segments and was rotationally grazed. Decisions regarding stocking rates and grazing pressure were made based on seasonal climatic conditions.
The pasture established in the PP system was a combination of lucerne, clover and medics. After an initial period of grazing, these treatments were only stocked periodically and the rotational treatments were not kept in place.
Results
- Soil organic carbon increased across all systems until 2008. In years from 2008 to 2012 there was a steep decline in soil organic carbon across all systems except for the pasture phase.
- During the CC treatment the phosphorous levels increased linearly at a rate of 1.8mg/kg per year of crop. This was due to the constant applications of phosphorous based fertilisers during the cropping periods.
- An interesting point to make is that the organic carbon within pasture system increased at a higher rate than the decrease in available phosphorous, which is largely inorganic. This means that phosphorous must have been provided from other sources. The only other alternative would be that soil organic carbon and plant available phosphorous were relatively independent of one another.
- The continuous cropping system exhibited soil degradation over the length of the experiment. The continuous cropping resulted in an increase in the availability of exchangeable aluminium ( Al+3 ) and a reduction in the availability of calcium carbonate (Ca+2 ).
- Sulphur showed consistently lower levels during the pasture phases when compared to the cropping phases.
Conclusion
The results have shown that under continuous cropping systems even though there is an increase in soil organic carbon as well as plant available phosphorous the soil health will still decline due to a reduction in Ph as a consequence of the continuous cropping phases.
Therefore in order to maximise the amount of carbon stored within the soil without negatively impacting the soils health the zero till system with no livestock and the traditional farming system proved to be the most effective farming systems.
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