Soil content

Socrates needs the Cation Exchange Capacity (CEC) of the soil. If CEC is not available then estimates are made from the clay % or the soil type. If you have the CEC value use this, otherwise Clay% or lastly soil type.

Clay %

Enter the % of clay in the soil as indicated on a soil test.


Enter the CEC (Cation Exchange Capacity) in mmol/kg as indicated on a soil test.

Initial OC %

Enter the OC (Organic Carbon percentage) as indicated on a soil test. As soils can vary quite widely due to past management, a starting value is important to obtain.


Start year (eg. 1990)

This is needed for the graphs and when stored weather data is used (See Simulation period in years).

Simulation period in years

This is the length of time the simulation will run. As changes are usually very slow, a period of ten years is a good starting point.

Simulation period in years

Must be in range - 1960 to 1990 (See Method of entering data - Closest town actual data).

Length of rotation in years (eg. Peas - Wheat would be 2)

The length of rotation or cropping/pasture sequence can be short (ie. 2) or very long if a non-repeating sequence is used. For example, if the simulation runs for tens years then a rotation can also be ten years. Other examples include;

  • Fallow - Wheat 2 years
  • Fallow - Wheat - Pasture 3 years
  • Wheat - Wheat - Pasture - Pasture 4 years


Method of entering data

Socrates offers the user the option to enter their own weather data in various ways including the use stored weather data from selected sites. The latter option allows different management options to be tested for a period where rainfall and temperature are known. For example, we could find out what would have happened if burning had continued at Walpeup during 1980 to 1990 compared to paddocks not burnt.

  • Enter yearly rainfall & mean temperature (Select and click to edit)
  • Enter average rainfall & mean temperature (Select and click to edit)
  • Closest town, stored weather averages
  • Closest town, actual weather data
  • Enter monthly rainfall & mean temperature (Select and click to edit)

Annual mean temperature

Enter the mean temperature for the simulation.

Average annual rainfall

The average Jan - Dec rainfall will be used for the period of the simulation. The Average annual rainfall window opens when this option is selected.

Closest town, average climate

The average rainfall and temperature for the selected town will for the period of the simulation. Once selected, chose the town closest to your particular station.

Closest town, actual rainfall (1960 - 1990)

The actual rainfall and temperature for the selected period will be used in the simulation. Once selected, choose the town closest to your particular situation. This option is very good for introducing variation and testing the effects of various management options.

Randomise annual rainfall

This option is only available when average rainfall is selected. This allows the computer generate variations in rainfall from year to year (+-30%) rather than the rainfall value being the same.


The amount of organic carbon added or lost from the soil varies between crops, pasture and fallow. It is also influenced by management factors such as burning of stubbles, hay or stubble removal, grazing and nitrogen application.

Information is entered for each of the rotations (There is a maximum length of 20 different crops or phases in one rotation sequence). The number of years is determined by the entry in the Length of rotation in years (Simulation section) box. For example, a Fallow - Wheat - Pasture rotation would have three years displayed with information required on the management of each phase of the rotation.

Options: For each phase of the rotation a crop, pasture or fallow option needs to be selected.

YearStubble managementGrazedFertiliser N
1...20 Enter whether the stubble is removed or burnt. Removal may be as hay, stubble harvesting or burning. Grazing is another form of removal. The intensity of grazing determines the amount removed. Enter the amount of nitrogen in kg/ha that is applied to the paddock.


Method of entering yields

Socrates requires dry matter production (kg/ha) for pastures and crop yield (kg/ha) for crops.

Enter annual yields manually

Enter grain yields (kg/ha) for crops and dry matter production (kg/ha) for pasture. You can use your own records or hypothetical values.
The yield is entered opposite the corresponding year. The yield figure is the yield of a crop or the dry matter production (pastures) in kilograms per hectare for that season. The total dry matter production (including roots) will be estimated from these figures.

Computer will calculate annual yields

When yields are not available, Socrates can estimate them using a modified form of the French-Schultz growing season rainfall (+ stored water) vs yield model (these can be modified by the user if site specific data is available, see next paragraph). We assume that during as average season crops and pastures will have available (before evaporation) approximately 70% of the growing season rainfall.


Organic carbon (%)

This graph reports the change in soil organic carbon (0-10 cm) based on the rotation, management, sol type and location.

Relative change in carbon

This graph is the relative change per annum in soil OC (%) expressed as a percentage (not the same at absolute OC % change).


The grain and pasture yields (kg/ha) each year

Table of management

this provides a summary of the crop/pasture and management imposed every year

Simulation Results

If you Select View Data

  • Crop - Crop of Pasture Type.
  • Rain - Annual rainfall (mm).
  • Yield - Grain or Pasture production (kg/ha).
  • Biomass - the amount of carbon left after removing grain and after grazing (if any), including roots.
  • Fert - the amount of nitrogen fertiliser applied (kg N/ha).
  • Urine - the amount of urine (as N) produced by the animals that graze the crop residue or pasture.
  • OC (0-10 cm) - the change in soil organic carbon over time in response to agricultural management (e.g. biomass, grazing, rotation).

The following are all expressed as CO2 equivalents (kg/ha)

  • N2O (fertiliser) - N2O produced from the application of nitrogen fertiliser - current 1% of nitrogen applied (kg N/ha). N2O Global Warming Potential = 296
  • N2O mineralised - the amount of N2O mineralised from soil organic matter.
  • N2O residues - the amount of N2O produced as result of the decomposition of crop and root residues.
  • N2O (indirect) - N2O produced from volatilisation and leaching of nitrogen applied as fertiliser and urine.
  • N2O (urine) - N2O from urine from animals currently 1% of total nitrogen in urine. This does not currently include N2O from dung from animals.
  • CH4 (animals) - methane produced from animals. CH4 Global Warming Potential = 34
  • Total - total greenhouse gas emissions
    As each year is calculated, the cumulative emissions (i.e. adding successive years) is displayed.