3.2 The following are determined from different aliquot parts taken from the same solution of the sample:
3.2.1 Total soluble nitrogen
3.2.1.1In the absence of nitrates, by direct Kjeldahl digestion.
3.2.1.2In 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
3.2.3.1In 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).
3.2.3.2In 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
3.2.4.1Solely in the presence of ammoniacal nitrogen and ammoniacal + nitric nitrogen, by applying Method 2.
3.2.4.2In 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
3.2.5.1By conversion using urease into ammonia which is titrated with a standard solution of hydrochloric acid,
or:
3.2.5.2By 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:
3.2.5.3By 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.