ISO/TR 7553:1987

Overview

ISO/TR 7553:1987 is an ISO Technical Report (type 3) that addresses fertilizer sampling and defines the minimum mass of an increment required to remain representative of the total sampling unit. Published by ISO/TC 134 (Fertilizers and soil conditioners), the report complements existing fertilizer sampling plans and sample-reduction guidance by specifying how far mass reduction may proceed before representativity errors become significant.

Key topics and technical requirements

• Scope: Applies when complete items are treated with a reduction device (not when using partial sampling devices). It sets limits on mass reduction beyond which sampling error cannot be ignored.
• Granular-product theory: Emphasizes that because fertilizers are granular, sample mass cannot be reduced indefinitely without losing representativity. Variability depends on particle composition and particle size distribution.
• Two product types considered:
  • Particles of the same nature (homogeneous): statistical treatment based on normal distribution of particle composition.
  • Particles of different nature (bulk blends): statistical treatment using binomial distribution for the least-abundant constituent.
• Calculation approach: The report provides equations and example tables that relate minimum increment mass to:
  • mean particle diameter,
  • particle density,
  • desired precision (error at set probability),
  • proportion of minor constituents,
  • a coefficient C that accounts for the number of dividing operations.
• Division and reduction guidance: Tabled values of C help users choose safe increment masses depending on how many reduction/division steps will be applied. The report warns that representativity errors accumulate with each reduction step.
• Practical precautions: Recommends crushing or grinding when reducing sample mass to maintain representativity; if grinding is not permitted, retain larger masses.

Applications and who uses it

ISO/TR 7553:1987 is directly useful for:

• Fertilizer manufacturers and production quality teams defining sampling protocols.
• Laboratory analysts preparing test portions and setting sample-reduction procedures.
• Quality control and assurance engineers ensuring compliance of sampling devices and reduction methods.
• Regulators and inspectors verifying that sampling yields representative results for composition, nutrient content, or particle-size analyses.
• Standards developers and researchers working on sampling plans and uncertainty quantification.

Typical applications include lot sampling, preparing laboratory samples for chemical analysis, and designing reduction procedures (grouping, dividing, grinding) to meet a specified precision.

Related standards

ISO/TR 7553:1987 complements other ISO fertilizer sampling and sample-reduction standards and sampling plans produced under ISO/TC 134. It should be used in conjunction with those standards when establishing complete sampling and analysis workflows.

Keywords: ISO/TR 7553:1987, fertilizer sampling, minimum increment mass, sample representativity, particle size distribution, sample reduction, sampling precision.