Royal Decree No. 1.110 / 1991 - Official methods of analysis of organic fertilizer products.
The present Royal Decree, which consists of 2 articles and 1 annex, approves the following official methods of analysis of organic fertilizer products: total humic acid and humic acids, degree of fineness, total nitrogen, amide nitrogen (urea), nitric nitrogen (method by Robertson), organic nitrogen, phosphorus soluble in water and in ammonium citrate (assimilable), water-insoluble nitrogen, total potassium, and free and total amino acids.