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Long-term performance of intensive cereal-based cropping in the Mallee

Bill Davoren1, Anthony Whitbread1, Rick Llewellyn1, David Roget2 and Gupta Vadakattu2

1CSIRO Sustainable Ecosystems, Waite Precinct, Adelaide Email bill.davoren@csiro.au
2
CSIRO Entomology, Waite Precinct, Adelaide Email gupta.vadakattu@csiro.au

Abstract

The Mallee Sustainable Farming Project initiated long-term plot based ‘core’ trials in 1998 at Waikerie, SA, and in 2002 at Paringi, NSW to compare the common low-input district farming practices of the time with alternative practices including intensification of rotations, reduced tillage and higher inputs. At Waikerie (calcareous sandy loam soil) the district practice treatment was a pasture-wheat rotation with low fertiliser inputs while at Paringi in NSW (“Belah” clay loam soil) the common rotation was fallow-wheat. These were compared with continuous cropping, higher input treatments with opportunistic break crops. The replicated trials were conducted for 10 and 6 seasons at Waikerie and Paringi respectively with monitoring of soil moisture, nitrogen and various soil and crop parameters. After 10 seasons at Waikerie the cumulative gross margin of the wheat-pasture treatment (ave. wheat yield 1.43 t/ha) was 37% lower than the intensively cropped treatment (ave. wheat yield 1.77 t/ha), largely due to two highly profitable cropping seasons in 2000 and 2001. On the heavier soils at Paringi where 4 of the 6 seasons of the trial have received less than decile 3 growing season rainfall, the cumulative gross margin from the wheat-fallow treatment (ave. wheat yield 1.45 t/ha) was 12% higher than the intensive cereal rotation (ave. wheat yield 1.06 t/ha). Over a trial period that has included a high frequency of low rainfall seasons the continuous cropping higher input treatments have performed well in terms of both yield and gross margin, however results demonstrate the importance of gaining high returns in better seasons.

Key Words

Intensive cropping, low rainfall, gross margins, continuous cereal, rotations.

Introduction

Cereal production in the low rainfall mallee region of Southern Australia (annual rainfall 250 to 350 mm) has been typically managed using low input farming systems which often failed to maximise yield potential and utilize the available rainfall of better seasons. This management system was in response to the low and highly variable rainfall patterns and also the low water holding capacity of the soils (Sadras et al 2002). Pasture-wheat and fallow-wheat rotations predominated and the poor performance of pastures and the high erosion risk associated with both pasture and fallow phases are significant impediments to sustainability. In response to the low adoption of modern conservation farming methods and low productivity gains in these regions of Southern Australia the Mallee Sustainable Farming project was initiated. The broad aim of the project was to improve the profitability and sustainability of broad acre cropping enterprises in the low rainfall, 250-350mm Mallee region of Southern Australia. This paper focuses on the yield-based results from these trials.

Methods

Long term plot based trials were established at Waikerie, SA (34 17’ S, 140 02’ E) in 1998 and later near Paringi, NSW (34O 61’ S, 142O 22’ E) in 2002. These trials compared the common district farming practices of the time with alternative practices including more intensification of rotations, reduced tillage and the application of higher fertiliser inputs. The performance of the main farming system treatments were compared in terms of grain yield and gross margin. At Waikerie (calcareous sandy loam) the ‘district practice’ treatment reflected a cultivated pasture-wheat rotation with low fertiliser inputs at sowing (5 kg/ha N, 11 kg/ha P) while at Paringi in NSW (Belah, clay loam) the common local rotation was that of cultivated fallow-wheat (6 kg/ha N, 13 kg/ha P). These “control” treatments were compared with direct drilled or single cultivation continuous cereal, higher input treatments (typically 27 kg/ha N, 16.5 kg/ha P) with the occasional inclusion of a canola break crop when early sowing rainfall and conditions were adequate. All fertiliser was applied at seeding at fixed annual rates that were not adjusted according to starting nutrient levels or seasonal conditions, stubble was retained in all treatments. Phased replicated trials were conducted for 10 and 6 continuous seasons at Waikerie and Paringi respectively. Various soil and crop parameters were monitored during the trial including soil nitrogen, microbial activity and microbial biomass (see Gupta et al 2008). Gross margins were calculated using average costs and grain prices of each system over the duration of the trial (1998-2007). Wheat and canola prices were estimated at $195/t and $375/t respectively, inclusive of freight, insurance and levies. Pasture (Sheep) income was estimated at $25/dse assuming 1.5 dse/ha. Total variable costs for the low input and high input wheat phases of the trials were approximately $100/ha and $160/ha respectively, using a MAP fertiliser price of $600t/ha. Average annual herbicide application costs in wheat were $34/ha for the continuous cropping treatments and $16/ha for the low input treatments. Wheat yields from the pasture-wheat and fallow-wheat treatments are from two phased treatments, gross margins from the average of both phases.

Results

Waikerie

Wheat yields in the intensively cropped treatment were significantly higher than in the pasture-wheat rotation treatments in 3 of the 8 comparable seasons and were never lower (Figure 1).

Figure 1. Crop yields (all wheat except for canola where shown) in the low input pasture-wheat and higher input continuous cropping (wheat with occasional canola crop) farming systems at Waikerie, SA from 1998-2007. Treatment columns shown with different letters if wheat yields were significantly different from each other at the P<0.05 level; ns = not significant.

In the first four seasons at Waikerie the continuous cropping system led to much higher gross margins over the district practice treatment, largely due to the relatively high gross margins from canola in 2000 and the following wheat crop (Figure 2). In the 6 seasons since 2001 there was a high frequency of low rainfall seasons and the cumulative gross margins of the two treatments were similar. After the 2007 season the cumulative GM of the wheat-pasture treatment was $1033/ha (ave. of pasture and wheat phases) compared with the intensively cropped treatment at $1639/ha, an increase of 59%. At Waikerie, the relatively poor pasture growth and associated low nitrogen fixation (<20kg/ha/yr) of the volunteer medic pasture has also contributed to relative profitability of the cropping-based rotations.

Figure 2. Cumulative gross margin performance of the low input pasture-wheat and higher input continuous cropping (wheat, occasional canola break crop) farming systems at Waikerie, SA from 1998-2007. Pasture-wheat gross margins show average of pasture & wheat phases in that year.

Paringi

Wheat yields have tended to be higher after fallow at Paringi, however this trend coincides with poor rainfall seasons (2002, 04, 06, and 07) and where rainfall was near average (2003, 05) the intensive cropping treatments have performed well (Figure 3). Average wheat yields of the wheat-fallow treatment (1.45 t/ha) are above both the continuous cereal rotation (1.06 t/ha) and continuous cropping (0.82 t/ha). Four of the 6 seasons received less than decile 3 growing season rainfall, this advantaged the fallow-based treatments, with the Paringi soils able to store some off season rainfall. The increased availability of nitrogen and potential for a disease break were also likely contributors to the yield improvements after fallow (Incerti et al. 1993).

Figure 3. Crop yields (principally wheat) of the low input fallow-wheat and higher input continuous cereal and continuous cropping (wheat, occasional canola break crop) farming systems at Paringi, NSW from 2002-2007. Treatment columns shown with different letters if wheat yields were significantly different from each other at the P<0.05 level; ns = not significant.

At Paringi, returns from the low input fallow-wheat treatment (cumulative GM $503/ha) are higher than the continuous cereal ($447) and opportunity cropping rotations ($431) (Figure 4). The positive cumulative gross margin for the continuous cereal treatment is largely the result of the $400/ha wheat crop gross margin in 2003.

Figure 4. Cumulative gross margin performance of the low input fallow-wheat and higher input continuous cereal and continuous cropping (wheat except canola in 2003) farming systems at Paringi, NSW from 2002-2007. Fallow-wheat gross margins show average of fallow & wheat phases in that year.

Conclusion

When the first of the trials were established over 10 years ago there was considerable uncertainty that continuous cropping rotations had the potential to be profitable in lower-rainfall mallee environments. The results from these trials show that despite a trial period with an unusually high frequency of below-average rainfall years, continuous cropping rotations with stubble retention (higher C inputs) can perform well. Similar to the findings of Sadras et al. (2003), the profitability of a higher input cropping system in the Mallee is largely dependent on the ability to alleviate the losses in poor seasons by capturing greater benefits from good seasons.

Acknowledgments

We thank Mallee Sustainable Farming Inc. and collaborating farmers Allen Buckley and Jim Maynard for there assistance and the Grains Research and Development Corporation for financial support.

References

Gupta VVSR, Roget DK, Davoren CW, Llewellyn R. and Whitbread A. (2008). Farming system impacts on microbial activity and soil organic matter dynamics in Southern Australian Mallee soils. These Proceedings.

Incerti M, Sale PWG and O'Leary GJ. (1993) Cropping practices in the Victorian Mallee. 2. Effect of long fallows on the water economy and the yield of wheat. Australian Journal of Experimental Agriculture, 33 (7) pp 885-894.

Sadras V, Roget D and Krause M (2003). Dynamic cropping strategies for risk management in dry-land farming. Agricultural Systems, 73 ( 3) pp 929-948.

Sadras VO, Roget DK, O'Leary GJ (2002) On-farm assessment of environmental and management constraints to wheat yield and rainfall use efficiency in the Mallee. Australian Journal of Agricultural Research 53:587-598.

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