David_Sweden Posted August 2, 2017 Report Share Posted August 2, 2017 I wanted to know what is the best action if one by accident applies double dose of liquid fertilizer: If it is best to just re-water with correct dose, or flush it heavily, or what? Couldn't get any good response so I tried to calculate this myself, see below. I don't know if anyone here is into the "scientific approach" at all, if you are, you are welcome to comment, since I never tried to calculate this before. So here it goes: I have a palm with 9L soil which drinks (up to) 3L water, and I usually use half dose of a Swedish liquid fert called Blomstra at every watering, which contains about 5g/100mL of nitrogen of which 3g is NO3- and 2g is NH4+. (Note: NH4+ are "cations", i e positively charged ions, and NO3- are "anions", and soil naturally has more or less negative charge, specified as "CEC", which holds on to the cations but lets anions get flushed out quickly.) Full dose of Blomstra is 4mL/L so for 3L of water I use 6mL Blomstra i e 2*(6/100) = 120mg NH4+ in Blomstra for one 3L watering. These say 360 lb./acre (pounds per acre) NH4+ corresponds to 1 meq/100g, where "meq/100g" is the unit for CEC, i e if CEC=100 for my soil (which is close to the truth if it is mainly peat and/or vermiculite at least) then there is 36000 lb/acre, and one pound is 0,454g and one acre is 4047m2, and assuming soil depth of 2dm this means 4047*0,2 = about 800m3 soil, meaning 36000*0,454g NH4+ per 800m3 soil, which is 36000*0,454/800 = 20g/m3 or 20mg/L NH4+, meaning that my 9L of soil has the capacity to store 180 mg NH4+. That should mean that the best action is to flush with plenty of clean water (which will flush out the NO3-, which is 60% of the nitrogen in this fertilizer) and not to water again with the correct dose. To water again with correct dose might make things worse. Actually, it is hard to say exactly what the situation with NH4+ will be, since the figures 120 and 180 mg are so close to eachother and my calculation rather coarse - perhaps rather much of it will be flushed or perhaps none of it, but much of it will remain in any case. And my calculations only cover nitrogen. If you have a low CEC soil, the situation is quite different. Then you should probably first flush with plenty of clean water, and then you may water with fertilzer but maybe a slightly lower dose than normally, perhaps half of normal dose. However, I'm thinking with low-CEC soil, you probably shouldn't use liquid fert, rather use slow release fert. I also think it is funny how instructions on my fert bottle takes no account of CEC of soil. Maybe they just assume everyone uses mostly peat moss like almost everyone does here in Sweden. Does anyone else but me find this interesting, or am I just the biggest nerd here? :-) 1 Link to comment Share on other sites More sharing options...
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