The growing tip and youngest leaves of my crop are dying and distorted, which nutrient causes this?

Death of the growing tip with hooked, distorted young leaves and brown dead margins most likely points to calcium deficiency, and sometimes boron, since both nutrients are immobile and are needed at the actively growing points. With calcium you typically see the youngest leaves and growing tips affected first, with deformed new growth, and in fruits it shows as disorders like blossom end rot in tomato or tip burn in leafy crops. Calcium moves with water in the plant, so the real cause is often not low soil calcium but poor uptake due to erratic watering, high salts, or rapid growth, which means fixing irrigation can matter as much as adding calcium. Please confirm with a soil test and look at your watering pattern before treating, because the same tip damage can come from boron shortage, drought stress or root disease. If calcium is genuinely low or the soil is acidic, liming with agricultural lime or gypsum before the season is the long term fix, and foliar calcium sprays such as calcium nitrate can help fruit disorders on a standing crop. Adjust to your soil test and local KVK advice and do not over-apply, and above all keep watering steady.