After three seasons of research trials and monitoring of farmer-managed focus paddocks in the low-rainfall Mallee, we have a far greater understanding of the potential for improvement of current farming systems and the practical considerations involved.
Take home message, times six
There is an opportunity to substantially increase productivity and profitability of mallee farms. This requires using the limited rainfall much more efficiently by minimising constraints to crop growth.
The focus paddocks have averaged 10.5 kg grain/mm of water used (growing season rainfall — 60 mm evaporation). However, results from selected focus paddocks and the core research trials have the potential to double this figure — 20 kg of grain can be grown for each mm of water used.
- Production improvements can occur together with significant benefits to the environment. Increased crop intensity with less cultivation can result in reduced wind erosion and reduced movement of soil water below the root zone (potential groundwater recharge).
- The key constraints limiting production identified to date include:
- lack or loss of soil nutrients including nitrogen, phosphorus and zinc. Nitrogen, in particular, can be very limiting in many cases due to limited mineralisation, poor fixation by legumes and leaching below the root zone;
- subsoil constraints. Subsoil factors such as boron toxicity, salinity, sodicity and high pH occur widely across the Mallee. These factors reduce the ability to store and access soil water and nutrients (particularly N);
- timeliness of sowing. Early sowing after the break is critical to use available soil water rather than lose it through evaporation. Where subsoil constraints are present, early sowing will help to limit soil water and nutrients moving to depth where the soil constraints limit availability;
- soil-borne disease. DNA assays (Predicta B) have been used to assess the importance of cereal root diseases. Although diseases, especially Rhizoctonia, are widespread, their impact on productivity is limited compared to some other yield constraints.
- Know your soils — monitor! To minimise yield constraints, the constraints need to be identified. It is very difficult to give general recommendations to address yield constraints due to the large variations that occur in mallee soils. David Roget downloads data from the weatlier station at Werrimull research site. Research is showing opportunity for big production increases across mallee country. Some variability in mallee soils is obvious (sand dune compared to swale) but other differences can be determined only by monitoring.
(See separate stories on variations in soils and erosion control p15, 16.)
Role of alternative crops such as oilseeds and pulses — these are important but limited in the Mallee. These crops provide a number of potential benefits including cereal disease control, alternative weed control and N fixation (pulses).
However, they represent a significant increase in financial risk compared to cereals. The risk of failure is such that they are not suitable for a fixed rotation system.
They need to be considered as opportunity crops to be used when seasonal conditions are favourable, i.e. good early break and full soil profile. When used in this way, canola has been shown to provide gross margin returns equal or higher than wheat.
Multiple cereal crops can be very successful Cereals provide the major profits for mallee farmers. The more intensively cereals are grown the more profitable the farming system can be. There is no inherent reason why multiple cereals should not be successful. The key to success is to monitor potential yield limitations (disease, nutrition, weeds) and address these issues as required.
The opportunistic use of oilseeds and pulses can be a valuable tool in addressing these limitations within the whole farm system.
Contact: Dr David Roget 08 8303 8528