Maximum Yield USA July 2017 | Page 56

calcium nutrition Many prone to tables are leafy vege , a calciu g tip burn developin issue. m-related What Does Calcium Do? Calcium is an essential macronutrient required for plant growth along with nitrogen, phosphorus, potassium, sulfur, and magnesium, and is typically supplied at rates of 80-240 parts per million in nutrient solutions. Calcium is a vital component of cell walls and membranes and is deposited during cell wall formation. Calcium is also required for the stability and functioning of cell membranes. When in short supply, cell membranes become “leaky” and cell division is disrupted, causing abnormal growth often in the form of a twisting or cupping of the newer foliage. Calcium is also important in maintaining quality and good shelf life post harvest by slowing the aging of plant tissues and protecting from toxins. Calcium is almost totally immobile in the plant, as it cannot be mobilized and moved around the plant once deposited in cell walls. Therefore, any deficiencies in calcium occur in the newest growth and include tip burn in lettuce, strawberry, and many other leafy crops, and blossom end rot of tomatoes and capsicum fruit. Other calcium deficiency symptoms vary between plant species and degree of severity. Apart from cupping of new foliage, other symptoms include a pale marginal band, yellowing, 54 feature water-soaked areas on foliage and stems, and root tips that can become almost jelly-like. Calcium deficiency can also be difficult to diagnose with foliar analysis as tissue of different ages commonly have varying levels of calcium. Older leaves may show sufficient foliar levels of calcium under analysis, but fruit or newly developing leaves or leaf tips of the same plant may have deficient levels—it all comes down to which part of the plant is sampled. Typical healthy foliar levels of calcium also differ between species. For lettuce, foliar calcium levels typically fall within the 0.8-2.0 per cent range; for tomato, 1.2–2.5 per cent; and cucumber, 2.0–4.0 per cent. Tip burn is one of the physiological problems that cool season salad crops are prone to in warmer climates and under greenhouse or growroom produc- tion. Some commercial growers have reported losses of up to 50 per cent of “ TIP BURN is one of the physiological problems that cool season salad crops are prone to in warmer climates and under greenhouse or growroom production.” their crop to tip burn at certain times of the year. What is highly detrimental is the tip burn that can occur inside the head of lettuce varieties that form a tight heart of leaves. While the outside of the plant may look perfect, when cut open, all the inner leaves can be severely affected by tip burn, which tends to form a blackened rotting mass as pathogens start to decay the dead tissue. While there are differ- ent types of tip burn, the most common form is caused by a lack of calcium in the tissue on the very edges of the leaves— when tissue is deficient in calcium, the cell walls begin to disintegrate and break down, resulting in dead leaves that then dry up or rot depending on how high the humidity levels are.