Soil Mineral Nitrogen (SMN)

Soil Mineral Nitrogen (SMN) usually has a bigger effect on crop growth, yields and quality than any other nutrient. Nitrogen can be supplied from the soil, atmosphere, organic manures and crop residue as well as from fertilisers. Nitrogen can be lost by leaching, ammonia volatilisation and denitrification.

SMN is an important analysis offered to the Brassica growing industry.

SMN analysis involves NH4 and NO3 and is calculated on a dry matter basis. From these results, the grower can then calculate the kg/ha requirements for the crop.

The measurement of SMN is unreliable if it is made soon after the application of fresh fertiliser nitrogen or cultivation. The mineralisation of nitrogen from previous crop residues also needs to be taken into consideration.

A loam analysis can also be carried out on the 0-30cm depth to give nutrient levels for fertiliser application.


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Soil Mineral Nitrogen (SMN) is normally sampled around planting time, before the use of any nitrogen fertiliser.

A minimum of 12 cores should be taken at two depths; the first to a depth of 0-30cm and the second between 30-60cm.

Sample at regular intervals, walking in an extended ‘W’ pattern across the whole sampling unit area.

The samples must be placed in a cool box containing an ice pack and delivered as quickly as possible to the laboratory.

On no account should the temperature of the soil be allowed to rise.

Bags can be supplied and posted out.