How should I mix hydroponic nutrient solution concentrates when cultivating ginger hydroponically?
Q: "I’ve been following Dr. Lynette Morgan’s advice for cultivating ginger hydroponically, found in the Q&A section of maximumyield.com. As per the recommendations for nutrient solution, I intend to use iron EDTA, manganese sulphate, boric acid, copper sulphate, sodium molybdate, zinc sulphate, calcium nitrate, manganese sulphate, monopotassium phosphate and potassium nitrate. I was wondering if it is OK to mix all the chemicals together in water or if I should separate one or more. If separation is needed, which can stay together without leaving any sediments at the bottom? Also, you have advised to switch to a fruiting formulation during the rhizome development stage. Can you recommend a parts per million) ppm concentration?"
A: Standard practice when making up hydroponic nutrient concentrates, which are stock solutions that you then further dilute with water to working strength to apply to the plants, is to separate the fertilizer salts into A and B parts. Part A has the calcium nitrate, iron EDTA and half of the weight of potassium nitrate dissolved into a given volume of water. Part B then contains the remainder of the potassium nitrate, magnesium sulphate, monopotassium phosphate, manganese sulphate, copper sulphate, zinc sulphate, boric acid and sodium molybdate. The reason why the potassium nitrate is split between the A and B stock solutions is to assist with solubility, as this fertilizer salt is the least soluble. Also, make sure your A and B stock solutions are made up into the correct volume of water so that all the salts are able to dissolve fully—use hot water to speed up this process. If there is too great a volume of fertilizers for the amount of water used in the stock solution, then oversaturation will occur and some of the salts will not fully dissolve.
The reason for this separation of fertilizers into A and B stock solutions when in a concentrated state is to prevent the reaction of calcium with sulphate and phosphate (calcium nitrate and monopotassium phosphate/magnesium sulphate), which causes insoluble white deposits to form, making these elements less available for plant uptake. For this reason, calcium nitrate is separated out into the Part A stock solution and the monopotassium phosphate and magnesium sulphate into the Part B stock solution. Once these stock solutions are diluted with water (usually at a rate of 1 in 100 depending on the EC required), these reactions don’t occur so long as pH is also within the correct range. It’s only in the concentrated stock solutions where precipitation is an issue.
When adjusting nutrient formulations from vegetative to fruiting growth (or in this case rhizome development), the ratios of macro elements needs to change to reflect what the plants will take up during this phase. The easiest way of doing this for any crop is to use hydroponic nutrient formulation software, which allows you to automatically adjust for each stage of growth and also for many other factors as well. While there are no standard nutrient recommendations for hydroponic ginger crops—ginger is not grown commercially on a large scale using hydroponics—my suggestion is to try potassium and calcium at the higher end of the suggested ranges for each: 240 to 260 ppm of potassium and 230 to 240 ppm of calcium, and to use leachate solution analysis to determine if these levels are sufficient, then adjust elemental levels as the plants mature.
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