Some base assumptions have been set up on the calculator. These are for guidance only and should be adapted for your own situation.

1. Enter your base yield. A good starting point is your long term average for the area in question. This calculator is base on cereals, so using wheat yield is suggested.
2. Enter a grain price – Use the long term net on farm values, say a five year average. Do not use current prices as these are likely to be misleading.
3. Enter a cost of sowing the crop. This should include all costs you include in your gross margin calculations (i.e. all direct costs)
4. This will leave you with a gross margin for the crop in question.
5. Enter spraying costs separately on a $/ha basis, this is measured also as a saving in the first 3 years after the mouldboard results.
6. Enter the cost of hiring or contracting a Mouldboard or Spader on a $/ha basis.
7. Enter your cost of funds. (if you are borrowing money then this should be at the cost of your overdraft. If you have credit funds in the bank this should be at the rate of interest you are being paid, or the rate of return you will get from investing the funds elsewhere)
8. Enter the expected change in yields from Mouldboard Ploughing/ Spading and the timing at which they are likely to occur. This is very subjective and will depend on the condition of the soil prior to Mouldboard Ploughing/ Spading.
9. The model also allows for break crop/pasture/fallow where little or no income is received from the area. Choose "No" into the pasture column.

The outcome is in 2 forms, an internal rate of return which reflects the effective annual rate of interest you will receive on the funds invested in the Mouldboard Ploughing/ Spading process. The second measure is the Net present value (in today’s $) of the income stream to you after considering the initial cost.

This calculator, like all on the Soil Quality website has been simplified to provide guidance to the relative benefit of upfront costs of using a Mouldboard Plough or Spader over time. Please note this calculator will only be as good as you assumptions.

Many soils in southern Australia are prone to non-wetting and recent trials have shown the benefits of using a mould board plough or spader every 10 years has lifted yields by burying non-wetting top soils to depths of 20 cm or more. Benefits include alleviating non-wetting soil, burying of weed seeds, loosening of the soil, and incorporating lime to depth.

While these treatments are showing some very positive results, they are very soil type specific. Make sure you know the likely agronomic responses of your soil types before using this calculator. Trial data will provide guidance in this area.

The aim of this tool is to allow you to conduct “what if analysis” of a rate of return and a likely response.