‘Pasture cropping' is a system where winter grain crops are sown over the top of summer active perennial pastures.  These summer active / sub tropical perennials are winter dormant and so are not very competitive with the winter crop.  ‘Pasture cropping' was pioneered by Colin Seis at Gulgong in NSW. 

Colin's cropping costs have reduced significantly compared to conventional cropping.  He has the added bonus of much better feed after harvest and in the years between crops.  Colin's observation is that ‘pasture cropping' actually increases the density of perennial pastures and this has been confirmed by university researchers.

Under this system of ‘pasture cropping' Colin has found that his cereal grain yields are as least as good as on perennials as when the perennials were removed with conventional cropping.  Again Colin's claims have been supported by research in NSW.  With no loss of grain yield, lower cropping costs and higher stocking rates the systems is much more profitable than the conventional system.

Soil tests from one of Colin's paddocks and a conventional paddock over the fence has shown a build up of soil carbon.  The additional carbon sequestered averages out over 17 years at 7.4 t/ha/year of CO2e.  This figure is very similar to sequestration rates under perennial grass and tagasaste on deep sands at Bob Wilson's farm at Lancelin. 

Of course as well as sequestering carbon in the soil there are also emissions from the farm such methane from livestock, burning diesel and electricity consumption.  Colin has estimated his whole farm emissions using a web based calculator.  The figures show that the farm has a net carbon sink of 5,000 t CO2e per year after accounting for emissions.  The farm sells a combined total 170 t of grain, wool and meat on average each year.  It is not possible allocate the sequestration to each type of produce, but on average there is 29 kilograms of CO2e sequestered for each kilogram of produce sold.  Similar calculations have been done for paddocks of perennial grasses and tagasaste on Bob Wilson's farm.  As Bob only runs cattle the carbon balance for beef alone can be estimated.  This was calculated as 25 kilograms of CO2e sequestered for each kilogram of cattle live weight sold.  At an assumed carbon price of $25 t.CO2e and a 50% meat yield, each kilogram of Bob's steak that is eaten has sequestered $1.00 worth CO2 from the atmosphere. 

These results must be considered with caution as the measurement intensity and emission models would not have the rigour of thorough scientific research.  However the results are remarkably similar for opposite sides of the country.  They also challenge a recent FAO report ("Livestock's long shadow") that suggests red meat production is adding to green houses gas levels in the atmosphere.  Eating meat produced from these perennial based systems may help reduce global warming!

Colin Seis has demonstrated over 17 years that it is possible to crop over sub tropical perennial grass in NSW.   But the soils and rainfall pattern there is very different to WA.  Can we successfully ‘pasture crop' in WA??

In 2007 we sowed wheat over an established perennial species trial at Dongara to test ‘pasture cropping' under our conditions.  A trial with a range of perennial grass and legumes species was sown at Len & Betty Metcalfe's on the Brand Highway north of Dongara in August 2005.  The site had one of the better loamy soils of the Greenough Flats.  Some of the more exotic legumes, such as stylos and lotus, failed to germinate and these plots became annual pasture controls.

In September 2006 herbicide treatments were sprayed diagonally across all the plots, with on strip left unsprayed as a control.  The aim of these spray topping treatments was to suppress annual weeds for the following crop and to study the effects of suppressing the perennial growth as well.

Wheat was sown over the whole site in July 2007.  The whole site was sprayed with 2 l/ha Sprayseed just prior to sowing with a disc seeder.  There was only 253 mm of rain at the site for 2007.  Plots were hand harvested in December 2007.  Grain yields from plots which were a) spray topped with 1 l/ha in the previous spring, and b) control plots which was not spray topped, are presented below.

Some perennials such as Bermuda couch, Kikuyu, Bambatsi panic, Lucerne and chicory substantially reduced the yield of wheat when there had been no spray topping in the previous spring.  With these species spray topping the previous spring increased grain yield when compared to their unsprayed controls.  Though for couch the yield was still less than the spray topped annual plots.  For all other perennial species, the yield of wheat on the spray topped plots was at least as high as on annual pasture plots. 

The wheat yields of the Setaria, Signal grass and finger grass on plots not spray topped were better than on the annual pasture which was not spray topped.  However the vigour of these perennial grasses were poor compared to the other perennials.  In contrast, the perennial legume Siratro had established and grown well.  The wheat yield on no spray topped Siratro was higher than on the no spray topped annual pastures.  Siratro is the most strongly winter dormant of all the perennials tested, and would therefore be the least competitive with the wheat during the winter / spring growing season.  Spray topping Siratro in the previous spring did not increase wheat yield.  The spray topping of this legume may have reduced nitrogen fixation which would benefit the following wheat crop.

The highest wheat yielding plots were the chicory plots that had been spray topped.  The chicory had been almost completely killed by the 1 l/ha of Glyphosate.  It was also observed that for the first two years after planting that the chicory had almost totally suppressed all the weed species (i.e. annual pastures) where as the other perennials had not.  There may possibly be some type of disease break in the chicory plots, but not with other perennials.  Chicory is not a true perennial and many plants die naturally after two seasons.  This trial suggests that chicory could play a role as a two year pasture in a crop rotation.

The results from this trial suggest that it will be possible to ‘pasture crop' in Western Australia without loosing grain yield.  This trial is particularly promising as 2007 was such a dry year.  Further work is required to test the concept and develop reliable management packages.