State Fertilizer Reporting & Regulations
AAPFCO Investigational Allowances
A commercial fertilizer shall be deemed deficient if the analysis of any nutrient is below the guarantee by an amount exceeding the values in the following schedule, or if the overall index value of the fertilizer is below 98%. Note: For these investigational allowances to be applicable, the recommended AOAC International procedures for obtaining samples, preparation and analysis must be used. These are described in Official Methods of Analysis of the Association of Official Analytical Chemists, 13th Edition, 1980, and in succeeding issues of the Journal of the Association of Official Analytical Chemists. In evaluating replicate data, Table 19, page 935, Journal of the Association of Official Analytical Chemists, Volume 49, No. 5, October, 1966, should be followed.
*For 52% available phosphate, the investigational allowance shall be 1.1 (Official 2011)
*For 62% soluble potash, the investigational allowance shall be 1.8 (Official 2011)
*For TSP the Investigational Allowance shall be: 1.53. (Official 2000)
For guarantees not listed, calculate the appropriate value by interpolation.
The overall index value is calculated by comparing the commercial value guaranteed with the commercial value found. Unit values of the nutrients used shall be those referred to in Section 11 of the Act. (Official 2003)
Overall index value - Example of calculation for a 10-10-10 grade found to contain 10.1% Total Nitrogen (N), 10.2% Available Phosphate (P2O5) and 10.1% Soluble Potash (K2O). Nutrient unit values are assumed to be $3 per unit N, $2 per unit P2O5, and $1 per unit K2O. (Official 1993)
10.0 units N x3= 30.0
10.0 units P2O5 x2= 20.0
10.0 units K2O x1= 10.0
Commercial Value Guaranteed = 60.0
10.1 units N x3= 30.3
10.2 units P2O5 x2= 20.4
10.1 units K2O x1= 10.1
Commercial Value Found = 60.8
Overall Index Value = 100(60.8/60.00)=101.3%
(b) Secondary and micro plant nutrients shall be deemed deficient if the analysis of any element is below the guarantee by an amount exceeding the values calculated according to the following schedule:
The maximum allowance when calculated in accordance to the above shall be 1 unit XE"unit" (One percentage point).
EXAMPLES:
Zinc guaranteed at: 0.75% Zn.
The investigational allowance is calculated as: 0.005+0.1(0.75) = 0.08%. A 'found' value for zinc of 0.66 (0.75-0.08=0.67) or less would be declared deficient. A 'found' value for zinc of 0.67 or more is within the investigational allowance for a zinc guarantee of 0.75% Zn
Zinc guaranteed at 36% Zn.
The investigational allowance is calculated as: 0.005+0.1(36) = 3.605; however, the maximum allowance is 1 unit (one percentage point). Therefore, the investigational allowance for a 36% Zn guarantee is 1 percentage point. A 'found' value of 34.99% Zn or less would be declared deficient. A 'found' value for zinc of 35.0 or more is within the investigational allowance for a 36% zinc guarantee.
Sampling.
Sampling equipment and procedures shall be those adopted by the AOAC International wherever applicable.
Breakdown of Plant Food Elements Within the Guaranteed Analysis.
When a plant nutrient guarantee is broken down into the component forms, the percentage for each component shall be shown before the name of the form.
EXAMPLES:
Total Nitrogen (N)................................................... ________%
________% Ammoniacal Nitrogen
________% Nitrate Nitrogen
Magnesium (Mg)..................................................... ________%
________% Water Soluble Magnesium (Mg)
Sulfur (S) ................................................................... ________%
________% Free Sulfur (S)
________% Combined Sulfur (S)
Iron (Fe)...................................................................... ________%
________% Chelated Iron (Fe)
Manganese (Mn)........................................................ ________%
________% Water Soluble Manganese (Mn)
(Official 1992)
Organic Nitrogen
If an amount of nitrogen is designated as organic then the water insoluble nitrogen or the slow release nitrogen guarantee must not be less than 60% of the nitrogen so designated. Coated urea shall not be included in meeting the 60% requirement. (Official 1994)
AAPFCO Investigational Allowances can also be found in the AAPFCO Official Publication.