determining you ph for soil

[GuFF]

determining your ph for soil

I would like to discuss soil Ph.

I believe that the reason soil Ph is "recommended" at a high Ph for ideal uptake is that the medium is drying out between waterings which is lowering the ph.

Now why does the Ph lower as the nutrient solution in the rootzone dries out?

Is it because some of the nutrients that drive the Ph upward are absorbed by the roots immediately and stored until needed? Such as nitrogen?

Now another thought of mine is that when someone wants to know what the ph of their irrigation solution for soil should be they should first consider their medium, does it drain fast? How much water does it hold between irrigations? Another thing to consider is their irrigation frequency, how often and how much?

Now, in dwc the prefered Ph is 5.3-5.8, this tells me that the rootzone prefers this range. So the trick with soil would be watering with a certain Ph so that as your soil dries, it gets into the 5.3-5.8 range. Just an assumption I would appreciate anyone elses knowledge on this.

Overall id say that the 'wetter' the medium stays the lower you should keep your irrigation Ph (6.0-6.3), that goes with saying that the grower is not having the soil so water logged that it is suffocating the roots of dissolved oxygen. One example is watering everyday in very small amounts. There is less of a 'dry out' period so there is less of a ph drop.

Now if the grower is watering a little more heavily and only watering say every 3-4 days then perhaps the grower should have his irrigation Ph a little higher (6.4-7.0) as the 'drying out' period is longer so the ph drop would be greater.

One thing i disapprove any grower of doing is running a Ph of whatever just because he was told by someone else it works for them, unless of course that grower is going to completly mimic that other growers set up (medium, nutes, irrigation frequency, pot size, lighting, temp, and humidity) because those factors will all play role in the water consumption by the plant and the tendency for Ph to fluctuate.

I am not claiming these are all facts, just my opinions from what i have read from other growers. A lot of what i have learned is from reading a lot of info from Lucas (creator of the lucus formula with the help of pH's nutrient calculator spreadsheet). I would greatly appreciate anyones thoughts and hopefully we can get a good amount of soil ph knowledge on this thread and good links to other good reads.

Cheers,
GuFF

 

[420king-MASSES]

well when i feed/water my plants the water ph is around 5.5-6.5 then i give plants the water/nute and when i come back to check medium ph it adound 7-7.5 due to the use of dolomite lime also my medium is promix with 20% perlite added in for quicker drainage my nutes are canna substra and the recomemded ph for the canna is 5.2-5.5

 

[Seamaiden]

Guff, are these all your theories, or what? You're going to really disapprove of me because not a one of my organic soil girls gets a second thought about the pH of their feed or water.

How do you know the pH of all soil situations drops as it dries out? I know mine rises if I try to acidify it, until it hits its own natural equilibrium. This is specifically because of the source water and its inherent alkalinity.

 

[420king-MASSES]

oh shnapp my homegirl about to drop some knowledge oh ya seamaiden im having ph fluctuation concerns myself can you maybe please shed some light for me
thank you kinger

 

[GuFF]

This is what I have read from lucas. I remember reading before that it depends on what nutrients are up taken from the plant and what is left over is where your soil ph will come from, from what i have read most nutrient profiles tend to lower.

If I'm not mistaken, beneficials drive your ph up, and 'bad' organisms like root rot drive your ph down because they release an acidic solution to make their enviornment more suitable for themselves.

And yes please 'drop' all the knowledge you can, thats why i made the thread. I would like to develop a good knowledge base from growers with past experience, trust me I won't take anything personally. What I said is from personal experience and previous reads, I never used organics and I always experince pH drop as nutes dry and accumulate in the medium.

420, If u want to discuss your ph problem on this thread please do so, I would like to learn from your experience as well.

Has anyone tried the blue lab soil pH meter? I have a Blue lab gaurdian and I think the soil meter only works with the blue lab combo meter which is not a continous read as the guardian is, or is it compatible with the guardian?

 

[GuFF]

Just curious seamaiden, what medium are you in and what do you feed with? What are you using to bring down your pH?

 

[Seamaiden]

I've been searching for the papers I've perused, unfortunately I don't think I'm using the right search queries, but I wanted to post up something that helped *me* understand *why* I am able to basically ignore my OD organic soil girls, when all others require a great deal more attention to grow and produce well. And that something is that, apparently, the plants and microbes are able to control the pH of their immediate surroundings to some degree by performing their own cation/anion exchanges. Plants can do this in the immediate root zone (rhizosphere?), I don't remember the mechanisms microbes use, though.

In my own experience this is absolutely true in the following circumstances: Outdoors, soil, organic/natural amendments. I find that when one of those three factors is changed then controlling pH becomes vastly more critical. Make the media coco, perlite, or water, even if outdoors, and you're going to have to pay much closer attention. Put the soil in pots and move it indoors, and again, you're going to have to pay much closer attention, and I'm not sure why this is, the main difference I can see is light source, i.e. the driver of the train, so to speak. Make the feeding chemical salts and, again, you've got to pay attention to pH and a bit more.

And so my OD girls (they're in a 3'x16'x2' planter) get straight well water, which we know will clog our drippers but there are products to blast that crap out. So does my husband's vegetable garden, which he's put together according basically the same way I did my garden (he's never gardened before, I have but on a much, much smaller scale).

For a long time I could not at all figure out why on earth the girls in this planter could take all of this terrible, hard, mineralized well water when nothing else can, not even my hardiest house plants. And then I read those couple of papers and it was like the Big Metal Halide in the Sky flashed off and on for me.

I'm still searching for the papers, I'm probably going to have to have a guy I know who loves pulling up this sort of stuff have a go at it. Or if Inuit were around, I betcha he could explain it far better than I.

I'm sorry, but I can't answer your question at all regarding the meter.

 

[GuFF]

What's your well water pH and ec/tds before any adjutments? Maybe a good deal of calcium in there driving up the ph?
after pH adjusting your water do you let it bubble or even just let it sit? I've noticed that water pH straight from the faucet tends to rise over 24 hrs in my experience.

Do u put em in the ground or do u just put the pot outside? When in the ground you don't have to worry about nutes accumulating in a pot, and the plant can get a small deal of nutrients from the ground, especially if you are on a slope! (rain water runs nutrient rich water through your root zone) Another trick i learned when growing OD is to put the plants in 5 gal buckets and use a pulley system to hang the bucket up in a pine tree, I guess they give off the same radiation as our favorite plant so no helicopter worries. Obviously dont put a Orange homedepot bucket up there lol

I notice a lot of nutrients are low in calcium and actually recommend tap water, obviously because not everone owns a ro filter. I like ro cause then I know excatly what the ec # consists of. but i have to agree its more coat effiecent to just use your water right out of the foucet as long as its not too high of a tds

I'm a medical grower so i cant do outdoors unfortunately but i sure used too ;) and i agree OD for me required much less attention, except keeping the damn animals off em.

 

[420king-MASSES]

i use tap water that gets bubbled for up to 5 days never less then 2 then when i feed i add my nutes and allow the nutes and water adjust and mix for 1-3 hrs then i go check ph if its in range i do not adjust but i always keep the tested water in the vial and normally about the day before the girls are due to get fed or watered the vials ph level is up there above 8 but my medium stays in the 7-8 area

 

[Seamaiden]

What's your well water pH and ec/tds before any adjutments? Maybe a good deal of calcium in there driving up the ph?

I don't have a water assay that would tell me exactly what's in there. It is an extremely deep well, had to go almost 800' to get rate. I cannot discuss qualities in terms of EC/TDS/ppm (yet, waitin' on a friend to get back to me about that meter), but I can discuss it in terms of general and carbonate hardness (in German degrees of hardness, I believe I've been misspeaking on this particular point as well, if so I apologize) and pH, as well as type of hardness (temporary versus permanent as determined by the boiling method).

So, well water is high in GH and dKH, 10* and 7* respectively. One is an indicator of the presence of carbonate and bicarbonate hardness, and the other is a measure of general hardness, which means it could be measuring almost anything--arsenic, cyanide, lead, iron, etcetera (not entirely out of the question considering both the area and activity of the last 150 years, along with assay reports from nearby public sources).

In any event, this is a temporary hardness that is reduced by a good 40%, my rough calculation, remembering that I am mathematically declined, by simply BOILING the water for 7-10 minutes, IIRC. Much of the mineral content will coagulate at the bottom of the pot and looks like a white mulm. I wish the iron that stains everything could be removed this way.

So, yes, there is a good deal of calcium as well as magnesium being likely, as well as the iron that makes our dirt red and stains the white stuff. And all of this drives up the alkalinity and pH, which out of the tap is anywhere from 7.8-9.0, usually around 8.0, and that alkalinity makes shifting pH by outside means not only extremely difficult, but difficult to keep shifted.

Yet, plants grown in organic soil situations outside seem to have no problems whatsoever with this situation.

after pH adjusting your water do you let it bubble or even just let it sit? I've noticed that water pH straight from the faucet tends to rise over 24 hrs in my experience.

That is because of the dissolved CO2 and O2 levels. O2 tends to drive pH upward (and the colder the water is the more O2 saturation, and the opposite is also true) and CO2 drives it downward. I've read that RO water is stripped of almost all O2 when it exits, I have to assume the same can be assumed of RO/DI (deionization), though I no longer have any O2 test kits. That is what I suspect is the reason for the shift, that plus the fact that it's been stripped of almost all minerals that would boost alkalinity (resistance to pH shift, or buffering capacity).

I do let the water sit and I do bubble it to both create surface agitation (which = best CO2/O2 exchange, occurs *only* at water's surface, bubbles' surface area quite insufficient & effect is negligible) and to allow nutrients and adjusters a little while to mix and, if they're going to, bounce.

But not with my OD girls in the planter.

Which I believe leads us to your next question...

Do u put em in the ground or do u just put the pot outside? When in the ground you don't have to worry about nutes accumulating in a pot, and the plant can get a small deal of nutrients from the ground, especially if you are on a slope! (rain water runs nutrient rich water through your root zone)

But I am on top of a very imporous/impervious clay, it takes water a long, long time to wick into it. The specific situation I'm discussing in which pH is not an issue is one I'll picture for you, large planter on the ground, open bottom with hardware cloth to keep out digging critters.

Another trick i learned when growing OD is to put the plants in 5 gal buckets and use a pulley system to hang the bucket up in a pine tree, I guess they give off the same radiation as our favorite plant so no helicopter worries. Obviously dont put a Orange homedepot bucket up there lol

I think my hempy tub girls are going to stand out. I've been waiting for the DEA flyovers, they usually start up between now and August. Either way, my back wouldn't allow me to do that, even though we're pretty surrounded by pines.

I notice a lot of nutrients are low in calcium and actually recommend tap water, obviously because not everone owns a ro filter. I like ro cause then I know excatly what the ec # consists of. but i have to agree its more coat effiecent to just use your water right out of the foucet as long as its not too high of a tds

I like working with RO, I hate the waste, it makes me sick.

I'm a medical grower so i cant do outdoors unfortunately but i sure used too ;) and i agree OD for me required much less attention, except keeping the damn animals off em.

Why can't med growers do OD? I've yet to have a problem with animals, except the motherfucking two-footed kind, if you get my drift. We have put measures in place to prevent that this year.

I've also had a support framework put in, both for the trellis and for me. The trellis adds another layer of protection as well as supporting the girls. The framework might allow me some extra time later in the season, too.

These girls were put into the ground in mid-to-late June. They're hitting about 8' now. I think they're a bit more airy than other girls their age because of some pines that block morning and late day sun. Unfortunately, the pines I really want to cut down belong to our neighbors.

 

[Seamaiden]

i use tap water that gets bubbled for up to 5 days never less then 2 then when i feed i add my nutes and allow the nutes and water adjust and mix for 1-3 hrs then i go check ph if its in range i do not adjust but i always keep the tested water in the vial and normally about the day before the girls are due to get fed or watered the vials ph level is up there above 8 but my medium stays in the 7-8 area

If you're using a colorimetric titration type of kit, don't do that. Always perform a fresh test according to directions. A lot of reagents can change color over time.

 

[420king-MASSES]

oh thank you so much so i should just retest instead of leaving in tube you just took so much weight off my shoulders and thats why your my water guru seamaiden i love it when you drop the knowledge

 

[Seamaiden]

It is truly my pleasure to know I've helped someone, especially if it leads to their further successes.

 

[GuFF]

Messed this post up, If a mod could delete it I would appreciate it.

 

[GuFF]

Found these online, any thoughts?

In low light ( overcast days or indoor growing environments) plants take up more potassium and phosphorous from the nutrient solution so the acidity increases (pH drops). In strong intense light (clear sunny days) plants take up more nitrogen from the n
utrient solution so the acidity decreases (pH rises). pH can be controlled in two ways.


Extremes in pH can result in precipitation of certain nutrients. For plant roots to be able to absorb nutrients, the nutrients must be dissolved in solution. The process of precipitation (the reverse of dissolving) results in the formation of solids in the nutrient solution, making nutrients unavailable to plants. Not all precipitation settles to the bottom of the tanks, some precipitates occur as very fine suspension invisible to the naked eye. Plants can tell us their problems through leaf symptoms (e.g. iron [Fe] deficiency) when it's too late. Iron (Fe) is one essential plant nutrient whose solubility is affected by pH which is why it is added in a chelated form (or daily), Fe deficiency symptoms occur readily. At pH values over 7, less than 50% of the Fe is available to plants. At pH 8.0, no Fe is left in solution due to iron hydroxide precipitation (Fe(OH)3 - which eventually converts to rust). As long as the pH is kept below 6.5, over 90% of the Fe is available to plants. Varying pH of summer lettuce nutrient solutions also affects the solubility of calcium (Ca) and phosphorus (P). Due to calcium phosphate precipitation (Ca3(PO4)2) the availability of Ca and P decreases at pH values above 6.0. All other nutrients stay in solution and do not precipitate over a wide pH range. Poor water quality could exacerbate any precipitation reactions that may occur. Generally in the pH range 4.0 to 6.0, all nutrients are available to plants. Precipitation reduces Fe, Ca and P availability at pH 6.0 and over .


Adjusting pH The addition of acids or alkalis to nutrient solutions is the most common and practical means to adjust pH, and can be easily automated. There are ways to minimise pH variations and they are worth some consideration. Nitrogen is the essential inorganic nutrient required in the largest quantity by plants. Most plants are able to absorb either nitrate (NO3-) or ammonium (NH4+) or both. NH4+ as the sole source of nitrogen or in excess is deleterious to the growth of many plant species. Some plants yield better when supplied with a mixture of NH4+ (ammonium) and NO3- (nitrate) compared to NO3- alone. A combination of NH4+ and NO3- can be used to buffer against changes in pH. Plants grown in nutrient solution containing only NO3- as the sole nitrogen source tend to increase solution pH, hence the need to add acid. But when approximately 10%-20% of the total nitrogen is supplied as NH4+, the nutrient solution pH is stabilised at pH 5.5. NH4+ concentration needs to be monitored as it has been shown recently that micro-organisms growing on plant root surfaces can convert the NH4+ to NO3-. Since hand-held ion-selective electrodes for measuring both NH4+ and NO3- are now available, it should be possible to accurately monitor and maintain a predetermined NO3-/NH4+ ratio throughout the life of the crop. Phosphorus is required in large amounts by plants. Interestingly, there are two forms of fertilisers containing both K and P - KH2PO4 mono-potassium phosphate (MKP) and K2HPO4 di-potassium phosphate. Equal quantities of both can be used to maintain the pH at 7.0. Using a higher proportion of K2HPO4 increases pH. MKP can be used to lower the solution pH. Buffers are solutions which resist pH change and are used to calibrate pH electrodes. Buffers can be added to nutrient solutions in an attempt to maintain pH stability. One such buffer is called 2-(N-morpholino) ethanesulfonic acid - abbreviated to MES. Many of the companies who claim better pH control with their 'specially' formulated nutrient solutions add MES to their mixes. It is important to remember when using MES, that after MES addition the pH is low and needs to be adjusted to your required level with an alkali such as potassium hydroxide (KOH). Another method of pH stabilisation is to use ion- exchange and chelating resins. Generally, these resins are small beads which have nutrients absorbed or chelated onto them - the nutrient solution circulates through the beads or the beads can be suspended in the nutrient tank. As plants absorb nutrients, more nutrients are released by the resins. The aim is to achieve controlled release of nutrients into the solution in an attempt to mimic the way the soil releases nutrients. Ideally, such release can adequately supply the growing plants' nutritional requirements and maintain pH stability.


Is pH Adjustment Critical? pH is not as critical as most hydroponicists believe. The main point is to avoid extremes in pH. Plants grow on soils with a wide range of pH. For most plant species there is an optimum pH in the region of pH 5 to pH 6.

pH values of natural waters are worthless!!

Yes! As a guide for determining how much acid or alkali needs to be added to change the pH by a required amount or as a measure of buffering capacity or corrosivity, experienced water chemists know that for reasons outlined below, that statement is true - especially when applied to natural uncontaminated waters such as scheme / tap waters and especially bore waters, with pH values within the range 4.5 - 8.2. Further, pH values within that range can be very unstable - i.e. variable over a short time period.

WHAT CHEMICAL CONSTITUENTS CONTROL pH?

a) In Scheme Waters and Bore Waters

Because of its solubility in water, the presence of carbon dioxide (CO2) in the atmosphere has a major influence on the chemistry and pH of water.

The pH of natural, i.e. uncontaminated, waters with pH values between 4.5 - 8.2 is controlled by the concentrations of bicarbonate anion, HCO3- (sometimes referred to as combined CO2) and free carbon dioxide - where the presence of free carbon dioxide in water lowers pH and bicarbonate elevates pH. It is the amount of bicarbonate (i.e. its alkalinity) in a natural water that determines its buffering capacity. Buffering capacity is the amount of resistance the pH of a water shows to additions of acid or alkali.

The presence of free, i.e. uncombined, carbon dioxide tends to lower the pH because it reacts with water to form carbonic acid thus:

CO2 + H2O = H2CO3

Contrarily, the presence of bicarbonate anion elevates pH because it mops up hydrogen ion thus:

H+ + HCO3 - = H2CO3

The overall reaction is represented by:

CO2 + H2O = H2CO3 = H+ + HCO3-

Thus at high CO2 concentrations the reaction is pushed to the right with the production of more H+ (i.e. pH is lowered). High bicarbonate levels (compared to CO2) mop up H+ with the result the reaction shifts to the left and a higher pH value is produced.


However, a complicating factor is that free carbon dioxide concentrations above about 0.5 mg/L in water are unstable when such waters are exposed to the atmosphere at sea level pressures. Under that condition carbon dioxide in excess of 0.5 mg/L will slowly escape from the water into the atmosphere. This is particularly the case with groundwater's which typically have carbon dioxide contents around 50 - 200 mg/L - as a result of biological activity within the aquifer. When these waters are pumped to the surface, the observed pH rises because the excess (acidic) carbon dioxide escapes. The pH will then rise to a stable value solely dependent on the water's bicarbonate content. For example, a bore water with 100 mg/L bicarbonate and 100 mg/L of free carbon dioxide will have an initial pH of 6.3 gradually rising to 8.2 after it has been exposed to the atmosphere and after which the carbon dioxide content has dropped to around 0.5 mg/L.

The same phenomenon although to a much lesser extent (because of their much lower CO2 contents), occurs with scheme (tap) water. Thus the conclusion - because the pH of natural waters are only stable after aeration, it is only the "after aeration" pH value which is stable and has any interpretative significance. To determine that value, aerate the water by tumbling a sample of it from one container to another, 30-40 times prior to measuring its pH.

In conclusion: interpret pH values with caution because a natural water with a lower pH than another may produce the higher pH after both are aerated!!

b) In Hydroponic Nutrient Solutions

Most commercial hydroponic nutrient concentrates contain no artificial pH buffers, free acids and negligible alkaline impurities such as bicarbonates and carbonates. Therefore hydroponic system pH values are essentially determined by the bicarbonate content of the water supply and the Phosphate content of the nutrient mixture only. Thus, with twin pack liquid nutrient mixtures, the pH of the working nutrient solution is usually determined by the pack containing the Phosphate i.e., the final pH is essentially not influenced by the presence or absence of the other pack in the diluted nutrient mixture.


Optimum pH for Hydroponics


The solubility of nutrients and their availability for uptake by plants in a hydroponic system is greatly influenced by the pH of the nutrient solution. Contrarily, although soil grown plants can grow successfully at relatively high soil pH values this is not the case in hydroponics where for nutrients to remain dissolved and suspended in the solution and therefore mobile, it is important to maintain the pH between 5.0 and 6.0 with an absolute maximum of 6.5.

Nutrients being constantly drawn from the nutrient reservoir and root exudate's entering the nutrient solution can change the pH of the nutrient. Consequently the nutrient pH must be checked and adjusted on a regular basis. pH fluctuations are less at larger nutrient tank volumes.

Keep the pH Between 5.0 and 6.0

It is over this compromise pH range that all growth factors are catered for to produce optimal growth. If the pH is allowed to rise much above 6.0, some nutrients, including calcium, phosphorus, sulfate (and the trace elements copper, iron, manganese and zinc) can precipitate thus becoming immobile and unavailable for transport by the water flow to the roots.

The precise pH at which precipitation starts is determined by the combined concentrations of calcium, phosphorus and sulfate. Except for fertilizer water mixture combinations with low concentrations of these nutrients this problem commonly occurs at pH values of around 6.5.

In spite of this precipitation problem, some references advocate pH values well above 6.5 for some plant varieties i.e., conditions which risk depleted concentrations of the above mentioned elements.

Before following such advice you may wish to test for yourself whether or not this problem will occur with your water and nutrient mixture by performing the following simple test:


Adjust the pH of your diluted nutrient solution to your target pH of 6.5, 7.0 etc., and place about 200 ml in a clean, clear glass container. Stir the contents continuously for approximately 1 hour. Then, immediately after briefly stirring, place the glass in front of a bright light and closely examine the contents. The presence of fine white particles or flocculate/gelatinous particles verifies that precipitation has occurred and that that pH value is too high for optimal results. If uncertain of the results, cover the glass with a piece of paper and allow the mixture to stand for 24 hours. Any precipitate will then be evident by the presence of a white deposit either floating on the surface or on the bottom of the container.

Notes:

(a) The stirring over the 1 hour period simulates the water movement in an NFT system and accelerates the rate of precipitation.

(b) The stirring prior to the visual examination is to ensure that all particles lift up from the base of the glass and into the viewing zone for easier detection. Also, it is much easier to detect the presence of small particles when they are moving.

Comment on Common Recommendation of pH 6.2

Although this is a commonly recommended pH value, it has no scientific basis. It appears to have gained a sort of mythology status from the early days when the only cheap means for hobbyists to measure pH was by using the common bromothymol blue pH indicator sold by pet shops for maintenance of the pH of fish tank water. Because the lowest pH value able to be determined by that indicator is about 6.2, those values have unfortunately, become an entrenched recommendation by the hydroponic retail industry.

High pH values (i.e. above 6.0) are to be avoided more than low values - i.e. say, between 4.5 - 5.0.

pH Adjustment

Before measuring the pH ensure that the nutrient is well stirred, especially after pH UP and DOWN are used.

If the nutrient pH is too high then add pH DOWN. Phosphoric acid is optimum for this purpose because it increases the nutrient's pH buffering capacity (helps minimize pH fluctuations) and is relatively safe to handle. Alternatively nitric acid has zero buffering capacity and is hazardous to use. Nevertheless, its use is preferable where high alkalinity waters are being used.

If the nutrient pH is too low then add pH UP. It is essential to pre dilute the pH UP dose into about 1 liter of raw water then stir the nutrient as you add this mixture. Failure to do this may cause permanent precipitation of essential nutrients. Also, when using "pH UP", precipitation problems can be minimized by ensuring the nutrient mixture is agitated rapidly near the point where the reagent strikes the surface of the nutrient. Also, if accidental overdosing to above 6.5 occurs, to prevent permanent precipitation and loss of essential elements, reduce the pH back, as quickly as possible, to below pH 6.0.

pH Up: pH Up contains 40% w/v potassium hydroxide. Contains no nuisance chemicals.

pH Down: pH Down contains 80% w/v phosphoric acid. This product is far safer than nitric acid and adds pH buffering capacity to the nutrient to help minimize pH fluctuations