Key points

• Modelling studies have demonstrated the potential profitability gains of including novel hard-seeded legumes in crop-pasture systems.
• Effective weed control is key to successful pasture legume establishment.
• Pastures should be well utilised, including during the year of establishment, and livestock should be run at optimal rates for the region.
• If pastures are ungrazed during the establishment year, or all years, there is a large reduction in profit from income loss from the livestock enterprise

Two economic modelling studies by CSIRO as part of the Dryland Legume Pasture Systems (DLPS) project have demonstrated productive legume-based pastures are profitable options in mixed-farming rotations in low to medium-rainfall regions.

Results showed that rotations including novel hard-seeded pasture legumes were profitable and had multiple roles in business diversification and reducing risk and costs. This comes from supporting a livestock enterprise and reducing year-to-year biotic stress and nitrogen input costs for subsequent crops.

Modelling components

The Land Use Sequence Optimiser (LUSO) and Model of an Integrated Dryland Agricultural System (MIDAS) bioeconomic models were used to investigate the economic performance of crop and pasture rotations, focusing on break crop effects that may persist across multiple years.

Considering crop and pasture phases in whole-farm economic analyses requires a deep understanding of value drivers and biological effects generated from both cropping and pasture sequences within a mixed-farming enterprise.

To gather this information as input data for the LUSO model, simulation modelling of crop (using the Agricultural Production Systems sIMulator, APSIM) and pasture production (using GrassGro) was conducted at Corrigin, in the Western Australian central wheatbelt. This dataset covered 30 years (1991–2020) and included inter and intra-seasonal variability.

MIDAS modelling scenarios were built for the WA central wheatbelt and southern Mallee of South Australia applying linear programming to maximise whole-farm profit of a representative production system, subject to resource, environmental and managerial constraints.

The central wheatbelt MIDAS was parameterised for six pasture legume scenarios considering establishment and maintenance costs, initial germination rates, average legume proportion in the sward, nitrogen content, dry matter digestibility and biomass produced.

Traditional legume species such as subclovers and medics were included in modelling scenarios together with DLPS hard-seeded legumes, such as French serradella, biserrula and bladder clover.

LUSO model simulations were conducted over six seasons to evaluate the economic returns of particular crop and pasture sequences. The model represents how each crop or pasture within a simulated sequence affects nitrogen, disease population dynamics and weed population dynamics, which then affect yield and economic return of subsequent crops.

Results

The LUSO-modelled profitability of different crop and pasture rotation sequences is shown (by phase) in Table 1. Results are for five-year average costs and prices and current prices averaged across high and low biotic stress scenarios for 1000 annual weather combinations. These were randomly generated from crop and livestock production simulated using 30 years of weather data.

Phases of novel pastures that were grazed (supporting a Merino sheep enterprise) were found to be more profitable than cropping phases for scenarios where five-year average costs and prices were used.

The most profitable rotation including pastures (PnPWPnCWW, Table 1) was $117 per hectare per year higher than the most profitable crop-only rotation (CWWCWW). The large loss from establishing novel pastures not grazed in the first season meant profitability was similar to the rotation with grazed volunteer pastures.

Table 1: Profit ($/ha) of five simulated roation sequences of six years, with combinations of wheat (W), canola (C) and volunteer (Pv), novel (Pn) and ungrazed novel (Pnug) pasture phases. Simulations were conducted using five-year average prices or current prices for wheat, canola and nitrogen fertiliser.

Source: CSIRO

higher profit from rotations with productive novel pastures was maintained in the sensitivity analysis conducted using current (higher) prices for wheat and canola and current nitrogen costs, with $88/ha/yr higher profit in the rotation that included grazed novel pastures.

However, under these conditions, wheat and canola phases following novel pastures were most profitable. The profitability of rotations with unimproved pastures was similar to continuous cropping rotations, except for continuous wheat, which was less profitable.

Further, we identified benefits in reducing risk, where rotations that included an annual pasture phase returned higher profit under the least profitable 20 per cent of seasonal conditions, compared with cropping-only phases. where scenarios had low biotic stress and used current (historically high) prices for wheat, canola and nitrogen fertiliser, there was no downside risk benefit from annual legume-dominant pastures.

MIDAS modelling

Whole-farm modelling results using MIDAS show significant profit potential when improved pastures become part of new optimised crop/livestock systems.

This was driven primarily by higher livestock production, reduced supplementary feeding and nitrogen fertiliser costs, but relatively little change in land use (i.e. about 10 per cent more pasture area and 5 per cent less canola area).

In WA’s central wheatbelt medium-rainfall region, biserrula, bladder clover and French serradella outperformed other options in economic value, resilience and sustainability.

Relative to the subclover baseline pasture, these three species increased whole-farm profit (37, 27 and 8 per cent respectively), increased sheep carrying capacity (50, 40 and 20 per cent), reduced fertiliser nitrogen inputs (-25, -20 and -9 per cent) and reduced methane intensity in terms of kilograms CO₂-equivalents per dry sheep equivalent (-11, -8 and -2 per cent) (see Figure 1).

Figure 1: Whole-farm profit (blue line) and proportion of arable farm under crop (orange area) and pasture (green area) for the six legume pasture scenarios evaluated on a typical 3750-hectare mixed farm in the central wheatbelt region of Western Australia (continuous cropping included for reference).

Source: CSIRO

In the South Australian and Victorian Mallee low to medium-rainfall region analysis, results suggest including a baseline medic pasture led to profit gains of more than 20 per cent compared with continuous cropping.

Replacing the baseline medic with an improved strand medic, Seraph , released through DLPS, increased potential whole-farm profit by a further 26 per cent.

Overall, the whole-farm crop/livestock analyses showed major profit gains are possible by using improved regenerating legume options achieved through greater pasture land utilisation, with higher stocking rates, while still maintaining a similar cropping program.

Alternative management tactics to reduce biotic stress and maximise profit were not considered, nor were any effects of conserved soil water in the prior season.

Structural changes to the enterprise mix of the baseline mixed farm were not overly important, with increased profit being driven bu higher stock numbers, reduced supplementary feeding costs and reduced nitrogen fertiliser cost.

the research supports a greater role for novel annual pasture legumes to enhance sheep production and benefits to following crops in low to medium-rainfall regions.

However, to achieve the benefits of higher profit and reduced risk, continued agronomic support is needed as growers implement complex management systems required to integrate new pasture legume species.

This research was part of the national Dryland Legume Pasture Systems project supported by the Australian Government Department of Agriculture, Water and Environment (DAWE) Rural R&D for Profit program and the Grains Research & Development Corporation, Meat & Livestock Australia and Australian Wool Innovation.

More information: Dean Thomas, dean.thomas@csiro.au, 08 9333 6671.

Read more:  Phases of novel annual pasture legumes are a profitable and low risk option in low-medium rainfall regions.