There are some hidden rules within the API calculations which can lead to discrepancies between values returned by the API and values in the paper version of RB209.
Some arable crops have a yield adjustment calculation as part of their recommendation. Therefore in order to calculate a recommendation, a yield is required. Where a yield is provided, this is used in the calculations. However, where one is not provided, a default yield will be used in its place.
The crops with default yields are (all in t/ha):
Spring & Winter Beans, Winter Oilseed Rape: 3.5
Peas: 4.0
Spring Barley: 5.5
Spring & Winter Oats, Spring & Winter Rye, Spring Triticale, Spring Wheat: 6.0
Winter Barley: 6.5
Winter Triticale, Winter Wheat: 8.0
Potatoes: 50.0
Sugar Beat: 60.0
Where the values in tables in Section 2 of the paper book are specified as 'ND' (No Data), these will be returned as nulls by the API.
While values in the same tables are: 'Trace' or '<0.1', these are set to 0.
Recommendation output values are rounded based on certain rules:
Values less than 10 are set to 0, values from 10 and above to less than 20 are set to 20, and all values from 20 and above are rounded to the nearest 5.
While Nutrients Supplied output values are always rounded to the nearest 5.
When calculating the SNS Index through the Field Assessment Method. If the field has not been in grass within the past three years, and the soil type is either an Organic soil or Peat soil. Then the SNS Index will be defaulted to the lowest value Index available during the calculations.
Therefore, for Organic soils, the SNS Index will be defaulted to 3. While for Peat soils, the SNS Index will be defaulted to 4.
Please note that if you have either Organic or Peat soils, then you are advised to consult a FACTS Qualified Adviser.