Soil Mineral Nitrogen
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.