Should I get a soil test or a leaf tissue test to confirm which nutrient my crop is missing?

Both tests help, and they answer slightly different questions, so the best practice is to use them together. A soil test, the basis of your Soil Health Card, measures what nutrients are present and available in the soil and the soil pH, and it is the right tool for planning your basal fertiliser before sowing and for spotting whether a micronutrient like zinc, boron, iron or sulphur is low in the field. A leaf or plant tissue test measures what the crop has actually taken up into its leaves, so it is the better tool when a standing crop is already showing symptoms and you need to know exactly which nutrient is short inside the plant right now, especially when soil has the nutrient but high pH or waterlogging is blocking uptake. So: use a soil test or your Soil Health Card to plan ahead and to set the season's doses, and add a tissue test mid-season to pin down a confusing standing-crop symptom before you spray. Please get one of these confirmations before spending, because symptoms alone can mislead, and remember disease and water stress mimic deficiencies. Once confirmed, correct the specific nutrient in the range your card and local KVK recommend and do not over-apply.