Whereas tissue analysisduring the growing season provides a more accurate guide to a crop’s nutrient status and the likelihood of nutrient disorders or deficiencies, particularly of micronutrients.
As a general rule, fields up to 10 Ha (25 Acres) in area can be sampled as one unit, providing each field is uniform e.g. with regard to soil type, past cropping, lime and fertiliser usage. Fields created by hedge removal are unlikely to be uniform.
Large fields, and fields which are not uniform, should be subdivided and each part sampled separately. Use a clean auger, hand trowel or spade (preferably chromium plated or of stainless steel). Carry a plastic bucket.
Individual samples, whether of soil, leaves or fruit, should be taken along a carefully well planned route across the field. The ‘W-pattern’ sampling path is adaptable to most shapes of field.
Start away from the gate, and avoid all areas which are not representative of the field as a whole such as head-lands, hedges, ditches, footpaths, fences, telegraph poles, sites of bonfires, fertiliser, lime or manure dumps.
Standard practice is to sample the youngest mature compound leaf (leaflet and petiole) early in the season from 30 plants. This corresponds to the fourth or fifth leaf from the top of the plant.
In mid-season, the 30 – 40 petioles are collected from the first fully expanded new leaf. The petioles should be bulked together from a range of locations in any field.
Take care when sampling for copper, zinc and manganese to avoid sampling leaves that have recently been sprayed with fungicides as they may be formulated with these elements and so give misleading analysis results.
Tuber peel analysis is a useful means of assessing calcium levels in tubers – calcium tends to concentrate in or just under the potato peel. However, as yet no standards for peel nutrient concentrations have been established.