Maximum Yield USA July 2017 | Page 62

calcium nutrition
New foliage in the center of celery plants may develop calcium deficiencies when humidity levels are high .

“ INDUCED CALCIUM DEFICIENCIES can also occur on certain substrates , particularly where organic materials may be used to support hydroponic plant growth .”

Other Factors that Influence Calcium Nutrition
When calcium deficiencies start to show , it is easy to blame a lack of calcium in the nutrient solution . However , this is rarely the case . Most well-balanced nutrient solutions run at the correct EC typically contain more than sufficient calcium for plant growth . Instead , calcium uptake and plant foliar levels are largely driven by the environment and linked to the rate of transpiration , but other factors also play a role with this element . These include the influence of the growing medium ( some of which may absorb calcium , making it unavailable for plant uptake ), EC levels , competition from other nutrient ions , and the health of the root system . In hydroponics , calcium nitrate fertilizer is typically used in nutrient products and formulations to supply calcium . This is highly soluble and rapidly taken up by the root system . However , the use of the ammonium form of nitrogen in nutrient solutions can significantly aggravate calcium uptake from the plants , despite optimum calcium being present in the root zone . This is because ammonium competes for the uptake of calcium . Lettuce and other leafy vegetable formulations in winter may incorporate as much as 15 per cent of total nitrogen as ammonium nitrate or ammonium sulfate , while the rest is available as nitrate ( either calcium nitrate or potassium nitrate . This helps boost growth under low winter light and temperature conditions and assists with pH control in recirculating systems . However , as temperatures increase in spring and summer , the formulation should be changed to one that contains only nitrate as a nitrogen source to help prevent the occurrence of tip burn in lettuce , blossom end rot in tomatoes , and the soft , weak growth that can develop from the use of ammonium under these conditions . Running very high levels of potassium can also worsen calcium deficiency issues . For this reason , maintaining the correct potassium to calcium ratio for each stage of growth assists with achieving optimum calcium levels in developing tissues . High EC levels also restrict calcium uptake by reducing the amount of water taken up by the plant in which calcium flows . In crops such as lettuce or tomatoes , which are prone to calcium disorders under warm growing conditions , dropping the EC assists with prevention of tip burn and blossom end rot and allows a higher rate of transpiration by the plant . The health of the root system also plays a vital role in calcium uptake . Root rot , over saturation of the growing substrate , or a lack of oxygen required for root respiration all restrict calcium uptake even when calcium levels have been boosted in the nutrient solution . Induced calcium deficiencies can also occur on certain substrates , particularly where organic materials may be used to support hydroponic plant growth .
One of these is coconut ( coco ) fiber or coir , a popular and versatile hydroponic substrate . In the early stages of growth , coconut fiber that has not been fully preconditioned can absorb large quantities of calcium ions , making these temporarily unavailable for plant uptake . A similar problem can exist with nitrogen draw down during the early stages of crop growth in coco . For this reason , selecting a suitable coco nutrient product or formulation with boosted calcium and nitrogen helps prevent early calcium deficiency problems . Once the coco substrate has been in use for a few weeks , this problem resolves itself and the fully conditioned medium then causes no further issues with calcium retention . Levels of calcium can be checked with use of nutrient solution analysis , which is particularly useful where coco and other organically based substrates may be in use . Nutrient solution samples can be taken from reservoirs in recirculating systems or as leachate / drainage samples collected immediately after irrigation in run to waste or open systems . Lab analysis of these samples then gives a good indication of how much calcium and other elements are available around the crop root zone .
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