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.
All samples must be accompanied by an appropriate field form to facilitate prompt and efficient processing.
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.
Mineral Nitrogen Acreage Excess - 50p/acre
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. A loam analysis can also be taken on the 0-30cm 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.
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.
Sample at regular intervals, walking in an extended ‘W’ pattern across the whole sampling unit area.
Preferred sample weight - 1.0kg
Minimum sample weight - 0.5kg
Place each sample in a separate, clean polythene bag, clearly labelled with a permanent marker as "0-30cm" or "30-60cm". 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.