Stubble Incorporation to Improve Soil Condition
Funded by Landcare Australia’s Workplace Giving Grants, the Cundare Duverney Landcare group have recently set up trials to investigate ways to improve the breakdown of crop stubbles incorporated into soil and improve soil condition. 
“Under our current cropping practices soil carbon is declining, which impacts upon the long term health of the soil” said Justin Alexander, President of the group.  “The burning of stubbles means about 80% of the carbon, nitrogen and sulphur goes up in smoke, along with significant amounts of phosphorous, potassium and magnesium”. To replace the nutrients lost by burning a 5 tonne per hectare stubble would require about 66kg of urea, 20 kg of single super and 58kg of muriate of potash.
Amount of Nutrients Lost by Burning Stubble

Nutrient	Wheat stubble nutrients (analysed 24/05/2004)	% Loss	kg/ha of nutrient loss  for 5 t/ha of stubble
Nitrogen	.63%	80	25
Phosphorus	.05%	44	-
Potassium	.31%	40	6
Sulphur	.08%	80	3
Magnesium	.10%	47	2
Carbon	48%	80	1920

Source:  Adapted from Maize Stubble Management Survey summary of results, Robinson and Kirkby CSIRO Land and Water Technical Report 13/02, January 2002.
Research shows that even under No Till cropping systems there has been found to be little to no increase in soil carbon, with much of the carbon in standing stubble lost to the atmosphere through volatilisation.  
While heavy stubble loads can be seen as a problem, an alternative is to see them as an asset, to increase soil carbon, improve soil structure, reduce soil shear strength (making for easier sowing and reduced fuel usage), improve root penetration and development to increase plant available water, and increase soil microbial activity to improve nutrient cycling and availability.
Work by CSIRO has found that to increase soil carbon, the stubbles need to be incorporated into the soil, where the clay particles and other elements such as iron help protect the carbon from loss through volatilisation.  However as some have found locally, the stubbles may not breakdown sufficiently prior to sowing and lead to problems such blockages and hairpinning at sowing, increased slugs, snails and disease problems, or yellowing of following crop due to lock up of nutrients.
The group is trying three treatments,

• Adding extra nutrients (ie. 5.6 kg N, 2.2 kg P and 0.9 S per tonne of stubble) to meet the biological demand of the microbial biomass to decompose the stubble, based upon the work of Clive Kirkby (CSIRO);
• addition of stubble digesters (beneficial fungi) to promote breakdown of cellulose in stubble to aid its decomposition and improve its’ digestibility by stock;
• addition of a blend of biological stimulants (comprising a mixture of humic acid, nutrients & coal dust) and stubble digesters to promote microbial decomposition of stubbles.

The wheat stubble loads varied from 6 to 10 tonnes per hectare.  Each treatment plot is about 4 hectares, and the treatments have been replicated at Justin Alexander, Rohan Turner, David Manfiold and Craig Beazleys, along with control plots. The additional nutrients and stubble digesters (beneficial fungi) were applied, and wheat stubbles incorporated around 10^th -15^th February, followed by some reasonable rains which helps to aid microbial activity.
“There is a cost associated the additional fertiliser and purchase of biological blend, however firstly we just want to see if we can get it to work regardless of the economics.  Then if it works, we can then see if we can make it viable” said Justin. “Also it’s a matter of the immediate cost versus the longer term benefits to soil condition, which it is difficult to put a value on.  We aren’t ruling out burning all together, however if we can reduce the amount we burn, or the frequency of burning for particular paddocks while improving soil health, then it could be a win win”.