The Fertilisers (Sampling and Analysis) Regulations 1996

Forms of soluble nitrogen

3.2  The following are determined from different aliquot parts taken from the same solution of the sample:

3.2.1 Total soluble nitrogen

3.2.1.1 In the absence of nitrates, by direct Kjeldahl digestion.

3.2.1.2 In the presence of nitrates, by Kjeldahl digestion on an aliquot portion taken from the solution after reduction according to Ulsch, the ammonia being determined in both cases as described in Method 2.

3.2.2 Total soluble nitrogen with the exception of nitric nitrogen, by Kjeldahl digestion after elimination in an acid medium of nitric nitrogen with ferrous sulfate, the ammonia being determined as described in Method 2.

3.2.3 Nitric nitrogen by difference

3.2.3.1 In the absence of calcium cyanamide, between (3.2.1.2) and (3.2.2) or between total soluble nitrogen (3.2.1.2) and the sum of ammoniacal nitrogen and ureic nitrogen (3.2.4+3.2.5).

3.2.3.2 In the presence of calcium cyanamide, between (3.2.1.2) and (3.2.2) and between (3.2.1.2) and the sum of (3.2.4+3.2.5+3.2.6).

3.2.4 Ammoniacal nitrogen

3.2.4.1 Solely in the presence of ammoniacal nitrogen and ammoniacal + nitric nitrogen, by applying Method 2.

3.2.4.2 In the presence of ureic nitrogen and/or cyanamide nitrogen, by cold distillation after making slightly alkaline, the ammonia being absorbed in a standard solution of sulfuric acid and determined as described in Method 2.

3.2.5 Ureic nitrogen

Either

3.2.5.1 By conversion using urease into ammonia which is titrated with a standard solution of hydrochloric acid,

or:

3.2.5.2 By gravimetry with xanthydrol, although biuret will also be precipitated by xanthydrol, this should not give rise to a significant error in the determination since its level is generally low in absolute value in compound fertilisers.

or:

3.2.5.3 By difference, according to the following table:

Case	Nitric Nitrogen	Ammoniacal Nitrogen	Cyanamide Nitrogen	Difference
1	Absent	Present	Present	(3.2.1.1)-(3.2.4.2+3.2.6)
2	Present	Present	Present	(3.2.2)-(3.2.4.2+3.2.6)
3	Absent	Present	Absent	(3.2.1.1)-(3.2.4.2)
4	Present	Present	Absent	(3.2.2)-(3.2.4.2)

3.2.6 Cyanamide nitrogen, by precipitation as a silver compound, the nitrogen being estimated in the precipitate by the Kjeldahl method.