CULTIVATION AND TECHNOLOGY Calcium deficiency has a major impact on yield Sufficient calcium in the soil does not guarantee sufficient calcium in the plant. Especially during prolonged droughts, a deficiency may occur resulting in symptoms such as internal rust. Even if there is no loss of quality, a calcium deficiency may result in lower yields. According to Ton Hendrickx of Crop Plant Solutions and Scott Garnett of Plant Impact, the foliar fertiliser InCa may offer a solution. “C alcium is a nutrient of which a plant needs quite a lot during the growing season. Calcium in the plant allows for permeability of cell membranes, cell division and cell elongation. The transport of this element in the plant only takes place from the bottom upwards. The intake of calcium is therefore only possible in a growing crop. For example, as opposed to sugars, calcium will never be going from the crop to the tubers. A grower should therefore make sure that there is sufficient absorbable calcium in the soil during tuber initiation. A deficiency can have a major impact on the growth of the plant and the quality of the tubers. A well-known phenomenon that is often seen here is rust spots in the tubers. If, during the growing season, there is no water shortage or other stress factors, there is usually nothing to worry about.’ According to Hendrickx, problems only arise in practice when there is water shortage. Complex calcium intake ‘If, due to drought or for another reason, a potato plant is under stress, calcium is needed to neutralise the production of harmful acids in the cell. The cell often takes this calcium from the cell wall which may even cause it to die. You may only spot this effect a few weeks later, but by that time, harm has already been done. A plant also becomes more susceptible to various diseases’, Garnett explains. Because a plant only transports calcium from the bottom upwards, a shortage in the foliage results in the extraction of calcium from Ton Hendrickx shows that InCa increases the marketable yield of a potato crop. the tuber. ‘In a physiological sense, the plant regards the tuber as a source of additional nutrients in hard times,’ Garnett emphasises. The extraction of calcium from the tuber may cause quality problems such as internal rust spots. ‘The problem is that there is often not enough absorbable calcium in the soil. If there is enough, calcium will only reach the plant if there is also sufficient moisture in the soil. A supplement of calcium through the foliage in dry periods gives poor results. This has to do with how a plant absorbs calcium in the cell. When absorbed through the foliage the growth hormone auxin plays a major role. A properly-growing crop only produces this hormone in the growing points. Most of the foliage can therefore not absorb calcium due to a 22 Potato World 2011 • number 3 Pagina 21
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