Lessons from a drought year ... and the year before about high input cropping in the Mallee by David Roget, Gupta Vadakattu and Bill Davoren, CSIRO Land & Water, Adelaide
The northern and southern farmer trials in this issue were compiled from the 2003 National Farm Groups' Manual published by the GRDC and Greenmount Press, which was supported by growers and the Federal Government through the GRDC. Copies are available free of charge from Ground Cover Direct free call 1800 110 044; email email@example.com
'Take home' messages
- In a very severe drought the key benefit of improved systems has been the stability of soils - reduced erosion risk - through stubble retention, particularly in no-till systems
- High-input intensive systems gave double the gross margin loss compared with district practice (wheat-pasture) in 2002.
- Gross margins over five years show high-input systems have returned double that of district practice.
- High-input intensive systems are, on average, profitable in eight out of every 10 years. The risk of higher losses in poor years is less than the risk of not realising benefits of better years.
- The value of reducing inputs in late-breaking seasons to reduce risk is not clear.
The 2002 season at Waikerie, SA, was one ofthe driest in 10 years, with an annual rainfall of only 125 mm (average 252 mm), of which 61 mm of effective rainfall fell in the growing season. Wheat yields were measured at 0.1-0.2 t/ha, but these were probably underestimated due to limitations with the harvester.
Canola was not harvested. There were no clear effects of previous treatments (tillage, rotation, fertiliser inputs) on final yield. But treatments that had nitrogen remaining at the end of 2001 (peas-pasture-fallow) showed better early growth and had greater yield potential.
Reduced erosion risk was a major benefit of the more intensive, no-till cropping systems where stubble was retained.
Long-term profitability of systems
Seasons like 2002 are to be expected on average once every 10 years, so the fanning system needs to be able to cope with them when they occur. Gross margins for all cropping treatments were negative in 2002, with losses in the high-input systems ($115/ha) approximately double that of the low-input conventional system ($66/ha).
But the high-input intensive opportunity cropping system has still produced over double the gross margin return compared to the conventional wheat-pasture rotation over the last five years.
The drought has provided an opportunity to test our understanding of the farming system at Waikerie in terms of both yield and economic performance for a range of different seasonal conditions.
As shown in the graph (on the next page), the high-input intensive cropping system outperforms the district practice system from an average of three years in 10 (decile 3) to eight years out of 10 (decile 8). The better performance of the highinput intensive cropping system is due to:
- higher yields through improved utilisation of available rainfall due to better matching of nutrient requirements (Note: Like much of the Mallee, medic performance at Waikerie is poor and the low nitrogeninput medics contribute to the reduced performance of the cereal-pasture systems.)
- improved supply and efficient use of nitrogen from increased microbial populations and activities due to increased residue input from stubble and roots
- more frequent cropping.
Managing the risk in higherinput systems
High-input, more inteusive systems can obviously result in greater losses in years of very low rainfall. It is tempting to consider reducing inputs in years with unfavourable starts to the growing season in order to reduce risk of loss. However, by reducing inputs, there is the risk of not taking advantage of favourable seasons.
Unfavourable starts to the season can actually result in reduced availability of nitrogen due to low microbial activity and may require higher use of fertiliser nitrogen to compensate. The best app-roach to managing risk is not clear-cut.
But with a potential of achieving economic benefits from high-input systems on average 7- 8 years in 10, it is likely the benefits of applying higher inputs, irrespective of early seasonal conditions, are greater than the risk of losses.
The difficulty in trying to pick seasonal responses has been demonstrated over the past two years where we have seen both record yields and a drought. In both years the first sowing opportunity occurred in the second week of June with minimal water stored in the soil (12 mm soil water in 2001; 6 mm soil water in 2002).
Program 4 Contact: Dr David Roget 08 8303 8528 email David.Roget@csiro.au
Region North, South, West