Anglian Soil Analysis Ltd

Soil Mineral Nitrogen

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. It is most important that reference is made to the SMN sampling guidelines below prior to any sampling being undertaken as SMN sampling is one of the most problematic of all sampling procedures.

Obtaining a reliable estimate of the soil nitrogen supply is an important step in optimising nitrogen fertiliser doses.

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

Sample at regular intervals, walking in an extended ‘W’ pattern across the whole sampling unit area. Adjust the angle of the ‘W’ to suit the shape of the field. A minimum of 12 cores should be taken at two depths, the first to a depth of 0-30 cm and the second between 30-60cm. A loam analysis can also be taken on the 0-30 cm depth to give nutrient levels for any fertiliser application.

Sample with a narrow diameter corer taking care to avoid cross contamination between the two levels.

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