Calculating mixing rate of ammonium sulfate for blueberries

fruitnut Z7 4500ft SW TXJuly 5, 2013

Mrclint was kind enough to post the link below concerning blueberry fertilization with ammonium sulfate, AS, 21-0-0.

If I'm reading correctly it says that at rates higher than 1.0 g/liter AS becomes a salt problem when growing blueberries. So I'm cutting that in half to provide a safety margin. That equals rounded off ~2 grams per gallon. AS weights 4.6 g per teaspoon. The rate I've quoted before was about one teaspoon per 2.5 gallon jug. That still seems about right and about 0.5 g/liter.

More accurate calculations says 2.5 gal equals 9.45 liter. So 1.0 teaspoon AS (4.6g) diluted in 2.5 gal equals 0.49 g/liter.

I know that's not real easy to follow but that's my calculation.

So I think 1 teaspoon AS per 2.5 gal water is a safe rate on blueberries in pots if there is a decent leaching fraction. It's been working for me and this literature says it's safe if properly used.

Here is a link that might be useful: Ammonium sulfate on blueberries

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bamboo_rabbit(9A Inverness FL)

Hmm......that is a bit lighter than I use. I have been using 4 cups to 300 gallons of acid treated water. I guess with our rains salt build up probably is not an issue.

    Bookmark   July 5, 2013 at 10:02PM
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fruitnut Z7 4500ft SW TX

Remember I cut the upper limit rate in half. And yes on your sand with your rain even the upper limit rate would probably be fine.

In pots it's harder to get even leaching so I built in a safety factor.

In 300 gallons I think as much as 1.2 liters, that's about 5 cups would be safe. But don't take that as an indication to increase your rate.

This post was edited by fruitnut on Fri, Jul 5, 13 at 23:27

    Bookmark   July 5, 2013 at 11:08PM
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Bradybb WA-Zone8

All this time,I thought your recommended dose was one tablespoon per two to three gallons of water.I'll need to correct that. Thanks,Brady

    Bookmark   July 6, 2013 at 1:34AM
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Yeah i was using one Half teaspoon per gallon of water on my potted blueberries. Have seen phenomenal growth using this mixture with no damage or buildup vs my first fertilization attempt at the beginning of the season. New to blueberries, but this method is working on my 6 potted plants. Picked some Polaris and Patriots this morning. Very Tasty.

    Bookmark   July 6, 2013 at 1:56AM
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All this time,I thought your recommended dose was one tablespoon per two to three gallons of water.I'll need to correct that."

I had thought and read the same as well. Although the granules don't all break down with the water when I add to a jug so they are obviously getting less than what I was giving them.

    Bookmark   July 6, 2013 at 11:21AM
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Posted to the wrong thread. Nothing to see here. :)

This post was edited by mrclint on Sat, Jul 6, 13 at 12:52

    Bookmark   July 6, 2013 at 12:50PM
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bamboo_rabbit(9A Inverness FL)


There are two versions of the is water soluble instantly and the other version takes some agitation to dissolve.

    Bookmark   July 6, 2013 at 1:14PM
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Yeah, I put it in the can and spray with hose and shake it, that dissolves some but not all. I guess you guys are using the water soluble type. I'll have to look out for it...

    Bookmark   July 7, 2013 at 12:07AM
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Do you have to worry about any leaf burn if some of the AS solution remains of the leaves of the plants?

    Bookmark   July 7, 2013 at 7:56AM
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bamboo_rabbit(9A Inverness FL)


I would imagine it would burn if the concentration was too high but at the rate Fruitnut advised? I think it would be ok. Might be something you would want to test on a single bush.

    Bookmark   July 7, 2013 at 8:28AM
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Just to clarify....would you BB fertilizers indicate if these rates are for every watering or an infrequent watering? 1/2 teas/gal is approx 125 ppm of N, I believe. Always good to talk about ppm of N.


    Bookmark   July 7, 2013 at 10:55PM
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fruitnut Z7 4500ft SW TX


The researchers were watering potted blueberries 2-3 times per week with a range of rates up to 3 times the rate I settled on. The highest rate caused damage. You might study the report I could be wrong.

I've mostly fertilized once a week but might go 2-3 times per week if wanting really fast growth. But I'd use pure water between fertilizer applications. You could probably get by using only the fertilizer solution but if doing that I'd run a large leaching fraction or cut the concentration more.

    Bookmark   July 7, 2013 at 11:15PM
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Hi Fruitnut,

So for I have applied 3 table spoons of Espoma Plant tone 5-3-3 organic fertilizer twice to my Blueberry plants in 10G containers in monthly intervals. After going thru this thread and few other threads, i'm thinking of using Ammonium Sulfate.

I used to water blueberry plants using rain water but now I acidify the tap water using battery acid to pH 5 and water the the plants.

Please help me with the below questions.

1. Can I add the Ammonium Sulfate directly to the acid water and fertilize blueberries when watering?
2. What is the ideal frequency for fertilizing potted blueberries with Ammonium Sulfate
3. You had mentioned that you would use pure water in between fertilization, does pure water equals tap/city water?

Appreciate your help.

    Bookmark   July 8, 2013 at 1:08PM
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fruitnut Z7 4500ft SW TX

1. Ammonium sulfate is safer dissolved in water before application. Applying granular and watering in is more likely to lead to salt burn IME. Also contributing to burn potted plants is applying fertilizer and not watering enough for periodic leaching.

2. It depends on how fast you want the plants to grow. I'm only in a big hurry on new plants that haven't fruited. There I might fertilizer 2-3 times per week. But even once per week can push pretty fast growth. After a plant reaches the size I want then it's once a week to once a month.

3. Pure water to me is rain water. Or if out of that tap water acidified to pH 4-5. Rain water is better if at all possible.

    Bookmark   July 8, 2013 at 1:49PM
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drew51 SE MI Z5b/6a

Thanks for the info here. BTW nandakumar mentioned Plant Tone. Which i think is an excellent organic fertilizer. It contains sulfur, and beneficial microbes also. Once plants reach maturity, it may be a better choice to use. And for those who wish to remain organic, it is the product to use.
I myself will be following my own advice once my plants are established. Once in a while I have to use tap water when out of rain water, so the continued use of sulfur is needed and this is a great way to do it all, Sulfur, microbes, and fertilizer all in one. It may have the trace minerals too, have to check.

    Bookmark   July 8, 2013 at 2:07PM
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bamboo_rabbit(9A Inverness FL)


Just understand that the sulfur in the fertilizer won't balance the bicarbonates in the water if the water is even fairly hard.

Just to add one thing to the excellent advice Fruitnut gave. Make sure you you don't apply the AS to dry plants. Best is to water them one day with normal water and fertilize the next day if you are even slightly concerned the soil is too dry.

    Bookmark   July 8, 2013 at 2:20PM
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drew51 SE MI Z5b/6a

Just understand that the sulfur in the fertilizer won't balance the bicarbonates in the water if the water is even fairly hard. "

Well only occasionally do I use city water. I only have 3 BB plants, and keep 100 gallons of rainwater. When it is 1/2 depleted, the last 50 gallons go for blueberries only. But once in a while I use the hose to really soak them. Like before I leave for a long weekend. Plus I do have sulfur on hand too! I prepared raised beds a year in advance with ton's of sulfur. And also added more twice this spring.
Currently I'm only using an organic for blueberries, and AS.
A couple years down the road, I'll probably use Plant-Tone.
My city water is 7.8 pretty high! Yikes! Again only used 3 or 4 times a year. Yeah the PH of the beds was around 4.5 -5.0 this spring, I would have to add a lot of city water to raise them above 6.0, I'm not concerned at this point.

    Bookmark   July 8, 2013 at 3:53PM
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Thanks fruitnut and all,

I got all of my 7 blueberries this winter and transplanted them to larger containers but still couple of them are yet to have any new growth/shoots. I think I may have to apply Ammonium sulfate probably twice a week to have nice growth and to expect decent fruits next year.

I think I missed to ask about the duration before, could you please let me know for how long I need to apply the AS, until fall end or even up to the next winter.


    Bookmark   July 8, 2013 at 4:31PM
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fruitnut Z7 4500ft SW TX


It takes about a month of frequent fertilization before the strong growth kicks in. Then you need to allow the plants time to harden up before cold sets in. So you've got a couple months of rapid growth if starting now. Don't push them hard once a real freeze is possible.

    Bookmark   July 8, 2013 at 4:39PM
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Drew, I would be real carefull with that sulfer. Its easy to over use and using the words "Tons of sulfer" give me chills. Ive had some bad experiences with sulfer. Alittle goes along way!

    Bookmark   July 8, 2013 at 5:45PM
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interesting discussion.

Would like to know whether applying ammonium sulfate can be considered as Organic?

    Bookmark   July 8, 2013 at 8:44PM
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Ammonium sulfate is not organic. Here's a video that shows a couple of small batches of ammonium sulfate in liquid form being mixed up. I'm not sure why he's cooking the powder at the end. Looks like a highlight from a "Breaking Bad" episode doesn't it? Non-organic growers take the crystalline form of either mix method, dilute with water and fertilize plants (including food plants) with it. Subway uses ammonium sulfate in their bread dough.

This post was edited by mrclint on Tue, Jul 9, 13 at 3:18

    Bookmark   July 9, 2013 at 2:16AM
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Follow-up on this thread,

it has been three weeks since I started applying AS to my blueberries and all of my plants now has new growth/sprouts. First freeze in Dallas usually occurs in the first week of Nov, considering this freeze timeline, please let me know when to stop applying AS to my blueberries.


    Bookmark   July 31, 2013 at 2:23AM
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Resurrecting a year old thread . . .
BR wrote:
I have been using 4 cups to 300 gallons of acid treated water. I guess with our rains salt build up probably is not an issue.If my math is right, that is 0.64 tsp/gallon. That is in comparison to fruitnut using 0.4 tsp/gallon. And, do I understand correctly, that in contrast to FN typically applying the solution weekly, you are using the 0.64 tsp/gallon every time you water? Or do you only periodically add ammonium sulfate to the 300 gallon tank?

As I've read suggestions from various extension services and other sources regarding per plant rates of nitrogen, I've noted wide variation. Almost all give rates for application of dry granules to the soil. Rates range (standardized to a per week rate - often given in application rates of monthly or every 4-6 weeks) from a high of 3/4 tsp per plant per week (OR State), to 0.12 tsp per plant per week (Arthur E. Gaus KS State) for young plants. Higher rates for older plants.

I'm not as amenable to the idea of dry granule application as I am to the dissolved application talked about in this thread, and in the ARS presentation FN linked to. I can see why many would be, as it is a pretty simple spread it and forget it method. If I understand correctly, salt burn to roots is going to occur as a function of concentration rate, which when applied as a solute, is known and controlled. Add a cup of solute, or drench the entire root zone, the concentration where the solute goes is still the same (or less, but never higher - unless the media does not receive enough water at once to flush it). Granular application could create localized hot-spots, and concentration is dependent on irrigation amounts and on the area over which it is spread. With a solute, even if you water 1/2 the plant's roots, those roots still will not be subjected to a concentration that will cause damage.

    Bookmark   April 23, 2014 at 6:18PM
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drew51 SE MI Z5b/6a

FN is using a very safe amount, you could easily double it, as stated in the first few posts. FN himself caculated BR could use even more and still be in bounds. But i too like the safe rate and take no chances. I only use it once a month anyway. I could double the rate with no issues.

    Bookmark   April 23, 2014 at 8:00PM
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I do 1 tablespoon of AS diluted in 4 gallons of water per bush, 2-3 times per week. They don't burn at all, but mine are in the ground and I kinda spread the solution over a wider area for maximum root coverage, so that alone may allow me to have a higher concentration and dosage per week.

I don't apply just water unless it hasn't rained in over a week, but in the spring that is mostly a non issue since it rains regularly. That is mostly during the summer when the plants need more water due to the heat.

I can attest that FN's strategy works well. My bushes have grown 2-3 feet since trying it out last July. I also use BR's battery acid strategy to bring the water pH down to around 5.

    Bookmark   April 23, 2014 at 9:24PM
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So you use a concentration of 3/4 teaspoon per gallon, with plain water (rain in spring, irrigation in summer) in between.

I agree that spreading 4 gallons over a larger area will let you get away with greater dosage but it won't let you get away with greater concentration. It's primarily the concentration that causes tissue damage.

    Bookmark   April 23, 2014 at 10:16PM
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bamboo_rabbit(9A Inverness FL)


I use the AS once a week. I only apply P and K once per year. There is a huge difference between growing in a pot and growing in the ground. My 3 BB beds are mulched 10" thick to try to retain as much moisture as possible and because of that I do not find it necessary to irrigate more often than once a week. If I did I would probably just use the overhead freeze protect sprinklers instead of the ground level micro spray heads and just use untreated water and then when I used the tank just drop the PH a bit lower than my normal PH 5 corrected water. Like I said though I have not found more frequent watering needed using my method. Note I said needed as in they show no water stress.

My plants grow like Windsors are pushing 8' tall even though they are pruned back to less than 5' each summer. The Sweetcrisps though are growing even more wispy which is not a good thing:) I tend to have to wade through a jungle to pick.

Would it be better to use half the amount of AS and water twice a week? Yes but while I am retired I have a LOT of plants....pushing 200 varieties of figs, grapes, blackberries, peaches, plums etc name it I have it and I only have so much time.

    Bookmark   April 23, 2014 at 10:36PM
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I have been using this method with AS with my blueberries this year so far so good little liners planted the end of Feb. have quadrupled in size my issue is and will be hard water, I do not have rain barrels yet and being in Peoria, AZ. there really isn't much to collect anyway so with the weather heating up I will have to be watering more obviously, will the AS be building up to much salt along with city water or will it even matter with the amount of salt in the city water, I have been thinking of a couple ways to lower ph in water by buying barrels filling with city water and soften with peat before watering or vinegar, I know it will not remove bicarbonates, I have also heard of using sulfuric acid to neutralize bicarbonates, but at what concentration?

    Bookmark   April 24, 2014 at 12:51PM
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Thanks for the additional info BR. I can’t recall how many blueberry plants you have even though I recall reading it previously. Presumably 300 gallons is enough to thoroughly wet the soil around each and flush out any buildup rather than allowing evap/osmosis to create a concentration situation. That was part of my primary driver for understanding if you fertigated each time, or periodically as others seem to do. I seem to recall that your primary irrigating season (dry season) is during fruit production, so thought there may not be enough rains to flush the mulch/soil. Apparently it is not an issue in your situation. I suppose that the microbes in the mulch also bind up some proportion of the nitrogen in composting it.

    Bookmark   April 24, 2014 at 1:39PM
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No one is going to be able to give you a recipe to treat your water with sulfuric acid without data on your water, and your acid concentration. It will depend on several factors. What you want to do is use just enough acid to reduce it to a pH of 5. That will neutralize about 80-90% of the bicarbonates. To figure out how much acid that is, you use titration. Fill a 5 gallon bucket with water, add a small amount of acid, mix, and test with pH testing strips. Add more if needed until you reach a pH of 5. From my tap, with better than average UT water, it takes about .75ml of 98% sulfuric acid per 5 gallons of water. At least you get periodic monsoonal flows down there to catch rain over the summer. Those flushes of rain rarely reach us up north of you. We are much drier (both humidity and rainfall) in the summer.

You won’t be building up too much salt in the media/soil if you make sure to flush it periodically. What you don’t want to do is to water in sips with just enough to wet the soil. Evap and plant uptake can leave the excess salts behind, building up each time. Periodically you want to thoroughly water the soil and have 25% or more of the water flow through and past the root zone. This will carry out excess buildup. Doing this with water not containing AS works very well, but doing it with AS of a low concentration will also work. A well draining soil/media will greatly aid in avoiding salt buildup.

    Bookmark   April 24, 2014 at 1:52PM
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bamboo_rabbit(9A Inverness FL)


How many bushes......that is a good question but currently somewhere approaching 200, I should end up with 240 or so when the Ravens are available and then the BB will be done. When I add the indigo crisps I will use those to replace other bushes, probably the 50 emeralds even though they are productive the berries are so so at best.

Btw I do not irrigate with 300 gallons it is 900 gallons.......the BB are in 3 distinct beds and each bed gets the 300 gallons of water with 1 cup of 96% sulfuric acid and 4 cups AS. In fact as we speak the last bed is getting irrigated.

If you want to figure out the dosage be my guest:) the back bed is 30x50' and has 6 rows of 13 bushes, so 78 bushes. So 78 bushes are sharing 4 cups of AS and 300 gallons of water.

    Bookmark   April 24, 2014 at 5:54PM
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I'll pass on dosage calculation, but thanks for the opportunity. :-) It is the concentration that is my primary consideration, as was the research linked to in the OP.

Here in 6b UT, my BBs are just now waking up. Leaves out on about 1/2, swollen buds on the other 1/2. Fertilization is top issue on my mind now that I have water acidification semi-automated.

    Bookmark   April 24, 2014 at 6:22PM
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bamboo_rabbit(9A Inverness FL)

How do you have it semi automated? Here I am just approaching peak harvest. Of course today I applied PH 2 water to one of the BB beds.

    Bookmark   April 24, 2014 at 7:07PM
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Venturi siphon. I intend to do a post on it when I get photos but I haven't taken any photos yet. Right now I have it hooked up to a hose and hose-end shower sprayer. But as I install the drip irrigation line I will be including an acid venturi injector on there. Probably a fertilizer injection line as well. The way I have it now I only have to touch the acid once every third or fourth week or so with the every-other-day watering of the 22 bushes. pH of 5 out the hose end.

    Bookmark   April 24, 2014 at 8:17PM
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Why Ph of 2?

    Bookmark   April 24, 2014 at 9:51PM
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bamboo_rabbit(9A Inverness FL)

Stupidity mostly:) I have a well pump mounted on a 300 gallon tank. In the tank is a float switch which shuts the pump off when the water in the tank gets too low. I also have a timed switch so I set it for 1 hour and at the end it kills the power..but it is bad have have not replaced it.

So I watered one BB bed and when it finished I started the water going in the tank for the next bed and set the timer on my phone for 16 minutes and when it goes off I know the tank is full and can shut the water off. So I start the water.set the timer.add the AS and the cup of 96% acid and walk away.....I forgot to unplug the float switch. So when the water level in the tank rose about a foot the float switch kicked the power to the pump back on. I was potting figs when I heard a noise...took me a minute to realize it was the ground level spray heads watering the center BB bed.....that is the reason I added the timed switch in the first place, to eliminate such things from happening. It is in fact the second time I have done it. I shut the pump down and just ran straight well water for 20 minutes so I'm sure they are fine. I need to get a new switch.

    Bookmark   April 25, 2014 at 7:50AM
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I have obtained a copy of the full paper whose technical abstract was linked to in the OP by Fruitnut. Here is the results and discussion regarding the portion of the paper dealing with ammonium sulfate concentration rates. The plants were tested in 8 liter pots with 1:1 peat and fir bark. For all concentration levels, the AS was supplemented with macro and micronutrients.
Leaf and new root dry weight were significantly affected by fertilizer rate (P≤0.05) and were lower when 1.5 g•L-1 of ammonium sulfate was applied than when 0 (leaf) or 0.25 (roots) g•L-1 was applied (Fig. 2). Plants fertilized with 0.75 and 1.5 g•L-1 also had lower leaf:stem ratios and allocated relative less biomass to new roots than plants given 0.25 g•L-1 (data not shown). Reductions in leaf:stem ratios were due to less leaf growth and to leaf senescence. Older leaves tended to become necrotic and drop from plants fertilized with 0.75 and 1.5 g•L-1 ammonium sulfate (ECw=1.5-3.0 dS•m-1; Table 1), which is a common symptom of salt stress in blueberry (Caruso and Ramsdell, 1995). Bryla and Machado (2011) and Bañados et al. (2012) observed similar symptoms of salt stress in ‘Bluecrop’ blueberry when plants were fertilized with ammonium sulfate at rates of 100-200 kg•ha-1 N during the first year after planting in the field. R.M.A Machado, D.R. Bryla, and O. Vargas, “Effects of Salinity Induced by Ammonium Sulfate Fertilizer on Root and Shoot Growth of Highbush Blueberry” Acta Horticulture (2014)

One reason I obtained the full paper were my questions regarding results at the 0.75g/l rate that were missing from the technical abstract. While stems and leaves did ok during the 8 week experiment under the 0.75g/l treatment, the difference in root growth rate between 0.25g/l and 0.75g/l is dramatic. 0.75g/l had just over 1/2 the new growth rate that 0.25g/l had. It does make me wonder whether or not stem and leaf growth at 0.75g/l would have measurably lagged behind 0.25g/l given more time.

Given the above, I am not as confident to presume that 0.5g/l is 1/2 of a potentially harmful concentration of ammonium sulfate. “Older leaves tended to become necrotic and drop from plants fertilized with 0.75 and 1.5 g/l ammonium sulfate” 0.3 might be a more ‘safe harbor’ level with some margin of error, but provide for vigorous growth.

Also of interest in the paper in confirmation that more frequent applications is generally advantageous. “On average, plants fertilized with ammonium sulfate produced greater leaf and root dry weights than those fertilized with urea and produced greater dry weight in all plant parts when fertilized 3 days per week or weekly than when fertilized every 28 days (Fig. 3). Ammonium sulfate also resulted in higher total plant N uptake than urea as well as significantly higher tissue N concentrations (P≤0.05) in both the roots (1.92 vs. 1.70%) and crown (1.21 vs. 1.07%), whereas frequency had no effect on N uptake and resulted in higher N concentrations in each plant part when plants were fertilized every 28 days than when fertilized three times per week or weekly (data not shown).”

I’ll add one more tidbit to this post from a different paper: David R. Bryla and Rui M. A. Machado “Comparative effects of nitrogen fertigation and granular fertilizer application on growth and availability of soil nitrogen during establishment of highbush blueberry” Frontiers in Plant Science (2006) As seemed logical (quite frankly, patently obvious) to me, fertigation creates much less “spikes” in soil salt concentrations as compared to granular application. Esp infrequent granular applications of larger doses as some have advocated.

The paper is publically available at Of note is the following graph regarding % of dead plants at different rates via fertigation and granular application. One weakness I see in this paper though is that the drip irrigation may have been only applying fertigation in between plants. A later paper, (D.R. Bryla, O. Vargas “Nitrogen Fertilizer Practices for Rapid Establishment of Highbush Blueberry: a Review of Six Years of Research” Acta Horticulture (2014)) touches upon this as they review different drip configurations and application of the fertigation directly to the roots.

The conclusion remains that fertigation results in less soil salt concentration than granular application at equal rates.

    Bookmark   April 28, 2014 at 12:39PM
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fruitnut Z7 4500ft SW TX


Thank you for the detailed accounting. I take it your recommendation is 0.3g 21-0-0 per liter. Which if my measure of 4.6g 21-0-0 per teaspoon is correct, I come out at ~0.25 teaspoon per gallon. And this might well be applied 3 times per week to max benefit. Does that sound right?

    Bookmark   April 28, 2014 at 1:22PM
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That is pretty close to the conclusion I'm reaching, from an armchair.

One difference: The only source I have for the weight/volume conversion of AS indicates 5.57 g/tsp. See I haven't broken out the triple beam balance and tried weighing some. And I suspect that there are differences between granule sizes by manufacturer that makes volume measurements less accurate (but probably plenty close enough).

So, at 1 gal = 3.78541178 liters, and 1 tsp AS = 5.57g, I get:
0.25g/l = 0.17 tsp/gal
0.3g/l = 0.20 tsp/gal
0.4g/l = 0.27 tsp/gal
0.5g/l = 0.34 tsp/gal

I don't know but what you have weighed your AS, but if it happens to actually be 5.57g/tsp, then at 2.5 gallons, 1/2 tsp = 0.3g/l.

If your 4.6 g/tsp is accurate, then I get:
0.25g/l = 0.21 tsp/gal
0.3g/l = 0.25 tsp/gal
0.4g/l = 0.33 tsp/gal
0.5g/l = 0.41 tsp/gal

    Bookmark   April 28, 2014 at 2:43PM
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Of course, for simplicity sake, I'll probably just use a slightly under-filled 1/4 tsp / gallon once a week for now.

I guess Oscar Vargas (jr author in two of the papers above) is in the process of writing his dissertation. I look forwarding to reading that.

    Bookmark   April 28, 2014 at 2:59PM
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Interesting read.

Although i do not have any experience when it comes to fertilizing Blueberries this way, i know from experience from growing other plants in pots that a lot comes down to the size of the container.

In the test they used 8 liter pots, and the less soil/substrate you have, the faster the build up of stacked salts will be. Bigger pots are a lot more forgiving.

When applied the same dose, i've seen plants in 12 liter pots killed, while the once in 25 liter flourished. Maybe one of the BB experts here can try this out on blueberries?

Using enzymes once a week on a flush day is also a good way to get rid of stacked salts. It will break 'em down and make them absorbable for the plants.

Excuse my bad english but i felt l had to share my experience. It is a missed chance they did not use different pot sizes in their test.

    Bookmark   May 4, 2014 at 8:38PM
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You make a good point and I would argue that the bigger the pot, the more fertilizer the plant can handle to an extent.

As I said before, my plants seem to grow just fine at 1tsp per gallon 2-3 times per week, but keep in mind they are in grown in-ground. Moreover, I have a thick layer of mulch that absorbs a lot of the fertilizer solution and I typically spread the solution over a wider area.

I would have loved to see if the results changed with bigger pots, because an 8 liter pot just seems too small for a blueberry bush.

    Bookmark   May 5, 2014 at 7:57AM
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Dosage vs concentration:

Pot size is not as critical of a factor as the method of application. I’m confident I could apply 1,000 grams of AS to a single plant in a single watering session in an 8 liter pot without any burn. As long as the concentration of the fertigation is low, the soil concentration level will not rise far above the fertigation mix concentration level when fertigation is properly applied (applied so that a portion of the fertigation solution flows through and drains out of the media).

On the other hand, I’m as equally confident I could burn a plant’s roots within a couple waterings with only 1/4 gram AS per liter of water in a 100 liter pot. Improperly applied fertigation ( applying just enough fertigation solution to wet the soil) will lead to accumulation in the soil, and high concentrations that will cause plasmolysis of the roots (burn). Been there, done that, even with very very small dosages of fertilizer.

There is a reason that the authors of this, and other studies, measure salts as a concentration, not a dosage. It’s the soil’s concentration that matters, and the best way to control that is via the fertigation/irrigation applied, and applying it in an appropriate manner.
For further reading see: Fertilizing Containerized Plants IV

    Bookmark   May 5, 2014 at 11:40AM
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I agree that pot size is not as critical of a factor as concentration, but pot size is still an important factor because pot size can affect root density, which would then affect the nitrogen absorption rate.

I would also consider pot drainage, soil medium, and dosage. The dosage will matter if it is too high and the pots aren't draining very well. Moreover, the soil medium will matter because certain mediums will absorb water more which will then keep that solution for the plant's roots to absorb for longer durations.

Those are just my observations, however.

This post was edited by ROFLwTIME on Mon, May 5, 14 at 15:20

    Bookmark   May 5, 2014 at 3:19PM
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When i watered my plants with an EC of 2.3 it killed my 12 liters, while my 25 liters showed no signs of burn at all. Also the residue water drained out of the 12 liter pots showed a much higher EC than that of the 25 liters. So in some way container size did matter.

On a hot day a lot of water evaporates from the medium, leaving the soluble fertilizers behind. This is where this size of the container starts to matter and why a bigger container is more forgiving. It can simply hold a lot more water, thereby slowing down the build up of stacked salts.

    Bookmark   May 5, 2014 at 7:45PM
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I recently purchased a bag of ammonium sulfate to try on my blueberries and it is in granule form as in the picture. It doesn't dissolve much in water. Is there a powdered form I could get instead? Or can I grind up this form with a mortor and pestle to make it dissolve better? I have struggled to find AS locally...only one farm store had it in the granule form. If a powdered form is better, anywhere online I can order it from?

Also, can I add this to my water+vinegar mixture? We have hard water and I'm using 1/4 cup vinegar with 2 gallons of water to bring the pH down to 4-5.


    Bookmark   June 3, 2014 at 8:25AM
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fruitnut Z7 4500ft SW TX

It's slow to dissolve even in small granules, not real slow. Best bet would be to give it 24 hrs and stir a couple times if possible. It could be ground up but that sounds like a mess and it will eat up steel tools.....and plant roots if not careful.

You could mix in with vinegar and water.

    Bookmark   June 3, 2014 at 8:47AM
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That doesn't look like ammonium sulfate to me. The stuff I have has no hint of brown in it and is completely transparent

    Bookmark   June 3, 2014 at 9:14AM
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Thanks guys. I left some in water and it finally dissolved so I will just pre-dissolve some before watering.

The link below shows that ammonium sulfate can also be brown

Here is a link that might be useful: white or brown

    Bookmark   June 3, 2014 at 9:59AM
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Bradybb WA-Zone8

After reading your post sharppa,I tried something.I have some Hi-Yield brand Ammonium Sulfate,probably not quite as big as the largest grains of your kind,but still somewhat chunky.
I took containers and put cold tap water in one and hot in the other,about 130F.After adding about 1/4 teaspoon of AS and gently swirling both,the hot water dissolved it in about a minute and after a few minutes,the cold water still had some solids.
So hot water will speed the process. Brady

    Bookmark   June 3, 2014 at 1:04PM
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At my local feed and fertilizer co-op--which I am lucky to have nearby--they offer AS in two forms. One is a water soluble crystal, and the other is pelletized. The pelletized form is usually harder to find. I like the water soluble when fertigating. The pelletized form is useful when spreading around the base of trees and bushes in early spring, when you don't want it dissolved and taken up all at once. It's a great fertilizer for acid-loving plants such as blueberries and pawpaws. My other fruit trees get pelletized urea, or a 19-19-19 if they need the other macros.


    Bookmark   June 5, 2014 at 11:31PM
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