Crop sowing into an established perennial pasture stand 2013 trial report

Background

Gatton panic grass and Rhodes grass are the two most commonly sown subtropical perennial pastures in the northern agricultural region.

Growth of these summer active grasses slows in winter.

This may provide an opportunity to grow a viable crop on land that has been sown to subtropical grasses (without removing the perennial base), however, both species present challenges when pasture cropping (that is, sowing annual crops into live perennial pastures).

Rhodes grass, with its long runners, is virtually impossible to crop into with tines; while Gatton panic grass, a bunch grass, can be ripped out with tines.

The options then are (a) to use a disc seeder or (b) to avoid cropping over species like Rhodes grass and use precision guidance technology (2cm autosteer) to seed annual crops between perennial rows.

Given that tines dominate in the NAR and the use of autosteer is now commonplace, we explored the second option.

Aim

To determine the feasibility of cropping into subtropical perennial pastures with tined seeders.

To evaluate the performance of annual crops when pasture cropped.

Trial details

Two perennial pasture blocks were established in August 2011 using precision guidance technology: 2cm accuracy autosteer with tines at 44cm row spacing.

One block was based on Gatton panic grass, the second was based on a wider range of perennial species including: Premier digit grass and Consol lovegrass, both upright bunch grasses adapted to light soil types (but not as productive as Gatton panic grass) and Burgundy bean, a tropical perennial legume related to Siratro (a species which has persisted in local trials but not proved to be very productive).

The establishment of perennials sown with precision guidance technology was excellent.

This has enable inter-row sowing of annual crops in subsequent years using 2cm accuracy autosteer and tines at 22cm row spacing.

Four separate trials were conducted on the site in 2013.

1. The impact of crop agronomy on wheat and lupin yield when pasture cropping into Gatton panic grass
2. The impact of perennial pasture species on wheat yield when pasture cropping
3. The impact of perennial pasture row spacing on wheat yield when pasture cropping
4. The impact of Clearfield technology on wheat and barley yield when pasture cropping

Results

Trial 1

In the decile 4 year, perennial pastures competed strongly with crops, significantly reducing yields.

Lupin and wheat were impacted similarly (approximately 33% yield penalty).

In 2012 (a decile 1 year) the yield penalty was similar for lupins, but larger (approximately 40%) for wheat.

Trial 2

Gatton panic grass was the most competitive perennial pasture species, which is not surprising given it also produced the most biomass.

The impact of Gatton panic grass on wheat yield was slightly less in plots where it had been established with a lower density.

By contrast, Burgundy bean was the least vigorous perennial species and had the least impact on grain yield.

Trial 3

Where the plant density of Gatton panic grass was lowered by establishing wider row spacing treatments, yield penalties were lower.

These lower density treatments more closely reflect local farmer paddocks, as the standard Gatton panic grass treatment in this trial are exceptionally dense.

Trial 4

Surprisingly, the use of Intervix® on the Clearfield® cereals did not suppress perennial grasses and boost grain yields.

Visual observations following the application of Intervix® found little to no impact on perennial pasture growth (unlike reported by Borger and Ferris 2013).

Weed pressure was very low.

Economic analysis

Analysis based on 2013 results (rainfall decile 4 year) found that the pasture phase needed to be at least three years before there was minimal difference between annual only and perennial grass based cropping systems.

Likewise, analysis based on 2012 results (decile 1 year) showed that three years of pasture followed by one year of pasture cropping out performed conventional crop/annual pasture rotations by around $60/ha or $15/ha/yr (Hagan et al. 2014).

Conclusion

Sowing annual crops into established perennial pastures with tined seeders can be done successfully, but forward planning is necessary.

Logistically, a perennial bunch grass sown with precision guidance technology on wide row spacings will facilitate sowing annual crops between perennial rows in subsequent years (that is, a viable pasture cropping system for growers with tined seeders).

Given that subtropical perennial grasses are currently sown on soils unable to support continuous cropping, perennial-pasture/pasture-cropping rotations may be profitable in the NAR even though pasture crops incur a significant yield penalty relative to annual only systems.

In addition, pasture cropping appears to offer flexibility to switch between crop and livestock production, and greater stability in income across years relative to annual-pasture/annual-crop rotations.

Acknowledgements

This trial was funded by the Department of Agriculture, Fisheries and Forestry Caring for our Country project.

This trial report is a summary of a 2014 crop updates article by Phil Barrett-Lennard, AgVivo. Thanks go to Phil Barrett-Lennard for taking a lead role in this trial and thanks to the DPIRD Geraldton Research Facility team for all their help with this trial, the EverCrop team for collecting the crop and pasture biomass data and the Gillam family for donating the land, seed and fertiliser.