Article 2-5 Calcium Build-up
Hi: I have a question for you about using Oxy-Cal. I noticed a slight yellowing between the veins on the leaves which appears to be caused by a Magnesium deficiency. According to Maximum Yield's latest issue on p.26, this could be caused by excess Calcium. I used Oxy Cal on the sunshine mix. Is it possible that I applied too much? I use General Hydroponics and follow their feeding program accurately. If I did use too much Oxy Cal, how can I reduce its affects and raise the Magnesium levels? Thank You for time, Matt
Some rather expensive studies by the Canadian Federal Government have been conducted on tomato plants with regard to the ideal calcium: magnesium ratio.
In hydroponic systems, 150ppm Ca : 50ppm Mg have been shown to result in greatest yields in control groups (all other factors being equal). Towards harvest in peat soils, the pH of the medium has usually become excessively low due to copious quantities of commercial fertilizer building up over a period of time. Magnesium becomes less available to the plant with decreasing pH. It is worthwhile to note that magnesium may not be the problem, but my response is assuming your diagnosis of magnesium deficiency is correct.
Studies suggest that excess potassium at the root zone is often suspect to locking out magnesium, which is the largest component of chlorophyll in higher plants. Reducing levels of potassium in the last few weeks before harvest, and maintaining a pH of 6-6.3 may help to alleviate this disorder.
Magnesium deficiency may not reduce overall yields, especially when the plant is putting it's final efforts into filling out blooms, as it is required most when leaves are rapidly developing. However, it may become a gateway for pathogens to enter the plant, thus, reducing yields. Some commercial vegetable growers are able to supply the majority of the crops magnesium requirements via frequent foliar sprays. Magnesium is also available in a chelated form (more available to the plant). Dolomite lime can help to maintain a stable pH, and contains magnesium. One cup of dolomite lime per cubic foot of Sunshine Mix can work wonders for many varieties.
I hope that this helps, and always follow the manufacturer/packager's directions carefully.