http://www.legislation.gov.uk/nisr/1991/540/schedule/2/crossheading/extraction-of-phosphorus-by-alkaline-ammonium-citrate-petermanns-method-at-ambient-temperature/paragraph/6/madeThe Fertilisers (Sampling and Analysis) Regulations (Northern Ireland) 1991Local GovernmentGovernment Printer for Northern Ireland2016-09-06AGRICULTURESCHEDULE 2METHODS OF ANALYSIS9fEXTRACTION OF PHOSPHORUS BY ALKALINE AMMONIUM CITRATE (PETERMANN'S METHOD) AT AMBIENT TEMPERATUREPREPARATION OF THE SAMPLE6See Method 1.