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Incorporating lucerne leys into cropping systems on the clay soils of the Darling Downs

N.P. Dalgliesh1, P.E. Tolmie2, M.E. Probert3, M.J. Robertson3, L. Brennan3, R.D. Connolly2, G. Sutton4, 4S. Hole, R. Taylor5, J. Grant5 and G. Milne5

1CSIRO Sustainable Ecosystems, Toowoomba, Qld.
2
Queensland Dept. of Natural Resources, Toowoomba, Qld.
3
CSIRO Sustainable Ecosystems, Brisbane, Qld.
4
IAMA, Dalby, Qld.
5
Participating Farmers, Jimbour, Qld.

ABSTRACT

The agronomic and economic implications of including a lucerne ley in an intensive, dryland, cereal-based cropping system is being explored using a participative on-farm research approach. Lucerne’s effect on subsequent fallow and in-crop water capture and storage are key determinants of success. Organic carbon has increased after 3 years of ley and the impact on soil physical condition has been positive with increases in soil conductivity within the top 30 cm of the profile. However, cumulative gross margins for the three years of lucerne ($373/ha) are significantly lower than the continuous cropping rotation ($950/ha). Long-term simulation indicates that recharge of soil water, after the ley, is likely to be a serious limitation to the growth of the first crop following the ley. Given these constraints, this paper looks at the potential soil physical benefits of including lucerne in the system and why a farmer may choose to forgo short term economic gain for longer term benefits. It also points to work being undertaken during the second phase of the project, which focuses on the length of ley required to provide positive soil benefits, longevity of that effect, chemical control of the ley and recharge of the profile.

KEY WORDS

Ley, lucerne, economics, simulation, on-farm, participatory, infiltration.

INTRODUCTION

Lucerne leys have been a component of northern agriculture for many years (3). In grazing systems, it is valued as a high quality animal feed (3, 7), whilst in mixed cropping areas it also contributes to nitrogen supply for subsequent cereal crops. Weston et al (6) found that, on a grey vertisol soil on the western Darling Downs, nitrogen accretion under a lucerne ley was between 80 and 105 kg/ha/year after a one year ley, and macro-porosity increased under ley pastures compared to continuous cropping. However Weston et al (6) and Dalal et al (2) both warned that inclusion of a deep-rooted perennial such as lucerne in the rotation may effect refilling of the profile in time to grow the following annual crop. Whilst lucerne has found acceptance in mixed cropping areas, it has had minimal impact where animals are not a component of the farming system, even though the beneficial effects, in terms of nitrogen accumulation, are well accepted.

The Jimbour Plain comprises heavy black vertisol soils (60-75% clay) supporting an annual cropping system (wheat, barley, sorghum, cotton and chickpea) with an intensity of approximately one crop per year. Double cropping is practised when conditions permit. Animals are not a component of the system. Due to high rainfall variability (annual rainfall for Jimbour 1890-1997: median 622 mm, range 241-1065), its summer dominance, and the ability to grow crops year round, farmers rely heavily on fallowing to store sufficient water for optimal production. Adoption of zero-tillage and controlled traffic (1) with improved equipment, pesticides and agronomic advice have contributed to increased crop production, but farmers still consider that there is scope for further improvement. This led to the decision to investigate the potential of leys. Although the farmers were well aware of the benefits of lucerne in improving nitrogen supply, this was not their primary goal. They considered that a ley, grown solely for this reason, would not be financially viable in their system; it was more practical to apply inorganic sources of fertilizer nitrogen. There would need to be additional benefits associated with growing lucerne, including an economic return from hay production and improved soil physical condition leading to increases in water supply for subsequent crops, for the ley to be a viable option.

A participatory on-farm research approach is being used whereby each of the collaborating groups (farmers, agribusiness and researchers) contribute to the research process, the skills and equipment unique to them. The farmers provide the land, equipment and farming expertise, the agribusiness participants provide the agronomic advice and access to a wider farmer discussion group through their client base, while the researchers provide the rigour in the on-farm research process and interpretation of the results in the context of the longer-term weather records, through simulation (4). Regular meetings with all collaborators provide a forum to discuss results, problems and research direction. Concomitant evaluation activities have allowed new ideas and insights emanating from the research to be incorporated into future planning.

MATERIAL AND METHODS

Sites were established on Waco (75% clay) and Bongeen (60% clay) soils on the Jimbour Plain, 40 km north-west of Dalby, on the Darling Downs. Both of these soils are heavy, black, cracking clays with high water holding capacity (250-300 mm for annual crops to 180 cm depth) and a depth of >3 m with no major chemical constraints to root extension. Plots ran the length of the field (800 or 1600 m) and were the width of two planter passes (20 m). No plot replication was possible, however four datum points were established along the length of each plot where all observations and soil and crop measurements are undertaken. Although a number of treatments were initially established, including the application of manure, a perennial grass ley and the intercropping of oats with lucerne, this paper concentrates on the comparison of lucerne and rotations of annual crops.

Plots of Pioneer L34 lucerne were established at each site in June 1997, using a zero-till planter on 38cm row widths. This resulted in an established population of approximately 650,000 plants/ha. These plots have been managed in a commercial manner with the farmers making all decisions including timing of baling; harvested material is sold to local feedlots. Quadrat and commercial yield estimates have been obtained at each harvest. The cropping systems being compared with lucerne comprise two plots in which annual crops are grown and managed to reflect the commercial operations of the farmers. Sorghum is grown on 75 cm row widths and winter cereals on 38 cm. Nitrogen (120 to 190 kg N/ha applied as urea) is applied based on prior crop usage and soil analysis. All operations are undertaken from controlled traffic tramways using zero-tillage practices.

Soil water, nutrients, organic carbon and soil permeability were initially determined in June 1997 and are repeated annually. Soil water and nitrate are measured pre- and post-crop, to 180 cm in annual crops and 300 cm in lucerne. Both soils have been characterised for plant available water capacity and for bulk density. The monitoring of annual yield of crops and lucerne, soil water and nitrate, in conjunction with daily automatic weather recording permits the simulation of the different cropping systems; long-term analyses have used the weather records for Dalby. Changes in soil physical condition are measured using disc permeameters (5) at a depth of 15 cm from the surface, the layer identified as constraining water infiltration during the initial benchmarking.

RESULTS AND DISCUSSION

Lucerne production

During the three-year ley, 27 t/ha of lucerne dry matter was produced on the Waco soil and 21 t/ha on the Bongeen, of which approximately 30% was baled. Dry matter production declined over time due to exhaustion of the sub-soil water. This caused a reduction in frequency of quadrat cuts (and commercial harvests) per summer season (from 4 and 5 in the first 2 years to 2 and 3 in the third), a reduction in biomass per harvest, and a failure in the third season to produce sufficient dry matter to warrant baling. The third season, which was dryer than average, highlighted the problem of attempting to grow lucerne solely on in-crop rainfall. This has led the farmers to consider that leys longer than two years may not be economically viable.

Crop production

Annual crops at both sites have produced cumulative yields of between 12 and 14 t/ha of grain (dry weight basis) from either the three or four crops grown during the three year period. These yields compare well with local commercial yields. Interestingly, district sorghum yields in the 1999-2000 summer, when no commercial production of lucerne was obtained from the third year ley, were some of the highest ever recorded (8-10 t/ha grain at 13.5% moisture). This is attributed to the seasonal rainfall distribution pattern (small amounts, often), which favoured annual crops over the deeper-rooted lucerne.

Comparing the short-term economics of lucerne production with annual cropping

This research has shown that reasonable gross margins are possible for lucerne although returns, for the full ley cycle, are lower than for annual crops. Whilst comparable to crops in the first year, yields and gross margins are much more variable in subsequent years, due to variability in residual stored water and the increasing reliance on in-crop rainfall. The period in which this trial has been undertaken has shown the disastrous consequences of a dry year on lucerne production, however local anecdotal evidence also suggests that the opposite can be the case, with high intensity storms providing high fallow efficiencies where the soil is cracked and receptive to water entry. Gross margins based on farmer-generated costs of production and yields, indicate that the ley has generated approximately $373/ha (for the full three year period) compared to an annual cropping sequence of three crops which generated approximately $950/ha.

Organic carbon

Organic C, in the top 15 cm of soil, has increased, in both the lucerne and annual cropping treatments, at both sites. On the Waco soil total carbon increased from 0.96% to 1.26% in the lucerne and to 1.16% in the annual crop treatments. On the Bongeen soil the change has been from 0.95% to 1.11% in the lucerne and to 1.16% in the annual crops. The increase in organic C in the cropping systems is no doubt due to the large inputs of crop residues. Dalal et al (2) found that for organic matter levels to remain at equilibrium, a rate of addition of organic matter of 1.4 t/ha/year (assumed 40% carbon) was required on a Waco soil. Return of organic material on both sites over the three year period totalled approximately 12 t/ha (dry weight basis) for the three–crop sequence (two sorghum and one wheat) and between 23 and 27 t/ha for the four-crop sequence (two barley and two sorghum).

Soil conductivity

Soil hydraulic conductivity was consistently higher on lucerne treatments than annual treatments for pooled 1998 – 2000 seasons, indicating a higher overall level of conductivity in the throttle layer (15 cm). As antecedent moisture conditions were consistently drier on lucerne treatments, more cracking of the heavy clay soils would have occurred throughout the seasons, giving rise to the higher conductivities measured. During the 2000 season, and to some extent the 1999 season, significantly more fine cracks (<750 μm) were measured in the throttle layer of lucerne treatments than were measured in other treatments, probably due to rooting structures. Increased numbers of finer macropores may be indicative of improved soil structure.

Soil water and nitrogen

Lucerne has extracted water to a depth of at least 300 cm and annual crops 180 cm. Figure 1 shows that for both soils, lucerne has the ability to extract more water from all layers of the profile when compared to annual crops. The ability to extract additional water in the top 180 cm, where annual crops are active, raises the question: will the different water use by lucerne and annual crops remain after the profile soil water has been replenished? One of the hypotheses being tested in the second phase of the work is that lucerne, through effects on soil physical condition, modifies the water availability for subsequent crops.

Figure 1: Water extraction patterns for lucerne & annual crops on (a)Waco soil and (b)Bongeen soil.

Killing the lucerne and recharge of the profile before the following annual crop is critical to the success of a rotation which includes lucerne. Other research in the area (2, 6) and local farmer experience indicates that it is not always possible to refill the profile. Long-term simulation of recharge undertaken as part of this project provides further evidence of the poor chances of recharging the profile. After killing lucerne in October, there is only a 1 in 10 chance of having >200mm of available water in May for the next wheat crop, whereas after a previous wheat crop the probability is 6 in 10. Furthermore, experience in this experiment highlights the difficulty of killing the lucerne. Attempts to spray out a two year ley achieved < 50% mortality. The surviving plants continued to use water and there was very little increase in water storage through the summer fallow. The issue of killing lucerne will be explored further during the second phase of the work with various chemical controls and cultivation being trialed.

CONCLUSION

Whilst the research is on-going, encouraging signs of change to soil physical characteristics, brought about by the inclusion of lucerne in the farming system, are emerging. Whilst it is too soon to draw conclusions about the optimum length of ley, there are indications that after as little as 1 year, lucerne may exhaust sub-soil water to 3m and later growth, relying on in-crop rain, may be poor. Together with problems of recharge after lucerne, this has led the farmers to consider a 1 or 2 year ley every 10 years as providing reasonable prospects for viable yields of lucerne and positive effects on soil structure. Whether this can also result in improved yield of annual crops after the ley, is yet to be determined. However if the farmers’ response to the interim results are used as a gauge of their intentions (>300ha planted to lucerne and substantial investment in hay making equipment), there is a future for lucerne which is not dictated totally by direct income from the crop, but from perceived longer term benefits impacting on subsequent crop yield and soil condition. This project provides a good example of participatory, on-farm research, harnessing the ideas, skills and expertise of a number of groups to explore an issue of interest and relevance, delivering experiences and insights which would be difficult to match using other research methodologies.

ACKNOWLEDGMENTS

This work is being funded by the Grains Research and Development Corporation under the auspices of the Eastern Farming Systems Project. Soil analytical services were provided by the Queensland Department of Natural Resources, Leslie Research Centre, Toowoomba.

REFERENCES

1. Chapman, W., Spackman, G.B., Yule, D.F. and Cannon, R.S. 1995. Controlled traffic development on dryland broadacre farms in central Queensland. Proceedings National Controlled Traffic Conference. Rockhampton pp115-122.

2. Dalal, R.C., Strong, W.M., Weston, E.J. and Gaffney, J. 1991. Sustaining multiple production systems. 2. Soil fertility decline and restoration of cropping lands in subtropical Queensland. Tropical Grasslands 25, 173-180.

3. Lowe, K.F. 1994. Understanding more about lucerne. In: Lucerne Management Handbook (Ed. K.F. Lowe). Queensland Department of Primary Industries. (Series: Conf. and workshop series QC93004).

4. McCown R.L., Hammer G.L., Hargreaves J.N.G., Holzworth D.P. and Freebairn D.M. 1996.APSIM: a novel software system for model development, model testing and simulation in agricultural systems research.Agricultural Systems, 50: 255-271.

5. Perroux, K.M. and White, I. 1988. Designs for disc permeameters. Soil Science Society of America Journal 52, 1205-15.

6. Weston, E.J., Dalal, R.C., Strong, W.M., and Lehane, J. 1997. Proceedings 12th Annual Conf Grasslands Soc. NSW. pp.11-17.

7. Weston, E.J. and Lloyd, D.L. 1988. Pasture Legumes-production constraints and prospects. In: Queensland Crop Production Conference Proceedings, 1987 (Ed: J.P.Thompson and J.A. Doughton). pp25-29. (Queensland Department of Primary Industries, Brisbane).

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