myxodex
Well-Known Member
I've spent many hours going through the fertiliser threads here, and I'd like to thank all the contributors to these discussions as I learned a lot.
ST is simply the best !
However, IMO there is one thing (almost) missing from the fert discussions and that is Sulphur. We talk about how much N to give and different forms NO3 vs NH4 vs urea, but how many of us stop and think whether there is enough S to "realise the availability" of the N we are supplying. Plants can only assimilate N if the available S is sufficient to do so. This is now understood in great detail down to most of the genes involved (useful review here : http://jxb.oxfordjournals.org/content/55/401/1283.short ). In western europe at least, reports of S deficiencies in crops (hitherto almost unknown) started to increase during the 1990's, and it has been blamed on the fall in industrial coal burning emissions of SO2 from the regulations (clean air act introduced in the 1980's). One thing that has been noticed is that when S limited crops are being fed with a high NPK (but low S) fert the NO3 run off is much higher than when S supplementation is given. In short, the S limitation has exacerbated the high nitrate problem in rivers.
I went through the very useful thread on fertiliser usage initiated by eOrchids. A sizeable majority who posted there use Klite, with kelp (or seaweed extract of some kind) as the most common supplement. Question is how many of you are using RO water ? For those who are using RO, the kelp extract may well be an important supplement for getting full N utilisation. If you are using tap or well water then there will most likely not be an issue as ground water almost always will have SO4 in more than sufficient quantities (worth checking this out i think).
The central issue is what is the ratio of S to N for orchids (Antec recommend 1/15). I did a lot of literature bashing to try and find any information but I found nothing specific to orchids, only a range of values for other plants from 1/15 (0.067) to 1/30 (0.033). The latter value is clearly a minimum at which most plants are considered S limited and at which most faster growing plants will show full-blown S deficiency.
If we use the 1/30 ratio as a "best case even if unlikely" scenario to calculate the maximum N availability given the amount of S in the fert alone we get the following table:
Fertiliser N - P - K effective NPK with RO water alone
Dyna Grow 7 - 9 - 5 1.5 - 9 - 5
MSU 13.2 - 3 - 15 3 - 3 - 15
Klite 12.9 - 1.3 - 1.3 3.3 - 1.3 - 1.3
Just check out what happens to the N/K ratio for MSU, a fert that is specified for use with RO. Klite comes out a lot better, almost like a dilution of 30-10-10. This all gets more complicated when growing on bark (or other degradeable substrates), because the microbes degrading the bark will also be using S, and very competitively at an S/N rate of 1/10, but once these microbes reach a stationary phase some of the accumulated S will start to be turned over and net microbial consumption will become insignificant (i.e. plants might be more prone to S deficiency within the first 6 months or so after repotting). So watch out for pale green to chlorotic leaves and do not expect the classic "new leaves yellow" symptom as it is unlikely in orchids, or even better still ... don't forget the kelp extract, which from figures I've seen, can be up to 3% S.
I hope this is helpful,
Cheers,
Tim
ST is simply the best !
However, IMO there is one thing (almost) missing from the fert discussions and that is Sulphur. We talk about how much N to give and different forms NO3 vs NH4 vs urea, but how many of us stop and think whether there is enough S to "realise the availability" of the N we are supplying. Plants can only assimilate N if the available S is sufficient to do so. This is now understood in great detail down to most of the genes involved (useful review here : http://jxb.oxfordjournals.org/content/55/401/1283.short ). In western europe at least, reports of S deficiencies in crops (hitherto almost unknown) started to increase during the 1990's, and it has been blamed on the fall in industrial coal burning emissions of SO2 from the regulations (clean air act introduced in the 1980's). One thing that has been noticed is that when S limited crops are being fed with a high NPK (but low S) fert the NO3 run off is much higher than when S supplementation is given. In short, the S limitation has exacerbated the high nitrate problem in rivers.
I went through the very useful thread on fertiliser usage initiated by eOrchids. A sizeable majority who posted there use Klite, with kelp (or seaweed extract of some kind) as the most common supplement. Question is how many of you are using RO water ? For those who are using RO, the kelp extract may well be an important supplement for getting full N utilisation. If you are using tap or well water then there will most likely not be an issue as ground water almost always will have SO4 in more than sufficient quantities (worth checking this out i think).
The central issue is what is the ratio of S to N for orchids (Antec recommend 1/15). I did a lot of literature bashing to try and find any information but I found nothing specific to orchids, only a range of values for other plants from 1/15 (0.067) to 1/30 (0.033). The latter value is clearly a minimum at which most plants are considered S limited and at which most faster growing plants will show full-blown S deficiency.
If we use the 1/30 ratio as a "best case even if unlikely" scenario to calculate the maximum N availability given the amount of S in the fert alone we get the following table:
Fertiliser N - P - K effective NPK with RO water alone
Dyna Grow 7 - 9 - 5 1.5 - 9 - 5
MSU 13.2 - 3 - 15 3 - 3 - 15
Klite 12.9 - 1.3 - 1.3 3.3 - 1.3 - 1.3
Just check out what happens to the N/K ratio for MSU, a fert that is specified for use with RO. Klite comes out a lot better, almost like a dilution of 30-10-10. This all gets more complicated when growing on bark (or other degradeable substrates), because the microbes degrading the bark will also be using S, and very competitively at an S/N rate of 1/10, but once these microbes reach a stationary phase some of the accumulated S will start to be turned over and net microbial consumption will become insignificant (i.e. plants might be more prone to S deficiency within the first 6 months or so after repotting). So watch out for pale green to chlorotic leaves and do not expect the classic "new leaves yellow" symptom as it is unlikely in orchids, or even better still ... don't forget the kelp extract, which from figures I've seen, can be up to 3% S.
I hope this is helpful,
Cheers,
Tim
