[VerdantGreen]

hi all, this study was posted elsewhere on the site but the thread sank without trace - i thought it was particularly relevant to Organic growers and wanted to see what you all thought.

https://www.usu.edu/cpl/PDF/Optimizat...er_Sources.pdf

High root zone pH reduces nutrient availability and high alkalinity water is strongly buffered around an alkaline pH. Soilless media can be altered to improve nutrient availability. This study was conducted to optimize the composition of soilless media for use with high alkalinity water. Mixes of peat and/or perlite or vermiculite in 50/50 and 33/33/33 volumetric ratios were tested. In some studies, mixes were also amended with up to 2.4 g/L of dolomite limestone to neutralize the initial acidity of the peat. Mixes containing vermiculite settled more, had higher water holding capacity (WHC) and percent plant available water (%PAW), and similar air filled porosity (AFP), compared to mixes containing perlite. Dry mass was measured in corn, peas, tomatoes, and soybeans, and chlorophyll content was measured in corn. The addition of dolomite increased pH and decreased dry mass in corn, soybean, and tomato, but peas were unaffected. Chlorophyll content in corn also declined with increased amounts of dolomite. After a week of daily irrigation, pH 7.8 nutrient solution neutralized the acidity of the peat, without the need for addition of dolomite. Mixes containing vermiculite improved growth and chlorophyll concentration compared to mixes with perlite. The higher cation exchange capacity (CEC) of vermiculite-containing mixes may have improved nutrient availability. A soilless mix of only peat and vermiculite, in approximately equal volumes, resulted in the greatest growth and chlorophyll content when watered with high alkalinity nutrient solution.

obviously the addition of compost, EWC and possibly topsoil would mitigate the effects of watering with alkaline water, but given the pretty fast and dramatic effects shown in the study, i doubt that it would negate the effects completely.

also worth bearing in mind that many organic P sources - such as rock phosphate and bonemeal - are also liming agents in their own right and may exacerbate the problem too.

i use citric acid to reduce the pH of my alkaline tapwater - and my plants seem to do great on it - but recently i wondered if this affect was temporary or permanent - afaik it depends on the type of alkalinity.

lastly, remember that pH and alkalinity are different.

pH is a logarithmic measure (that is, every 1 unit change is a factor of 10) of the concentration of hydrogen ion and that determines the acidity of the solution (acidic if pH < 7). In the opposite direction away from neutrality, at pH > 7, the solution is basic aka alkaline which would be the case for your solution with soda ash. TA is a measure of any chemical species that can accept hydrogen ions so if the TA is high such species combine with the hydrogen that is added from acids such that the effect on pH is far less. Soda ash not only increases pH, but it also increases TA a lot as well. This basically means that though the pH may be measured as high from the Soda Ash, you can't tell how much acid you need to add just from the pH -- you need to know the TA or more easily use the acid demand test as indicated above.

VG

[LAMBS-BREAD]

Very good info. Like u could have vermiculite for veg and perlite for bloom?

[VerdantGreen]

interesting idea LAMBS - why do you think that would be better?

tbh i took more notice of the lime and pH stuff, need to read it again about the perlite/vermiculite thing

VG

[skullznroses]

I know this is pretty true from experience. I have to adjust the PH of my water from 8 to about 6.5 before I use it. Even so I have found that using a promix based soil mix that I would have slight micronutrient issues. I started adding lime to my promix soil and that helped, although lime can burn roots too. After some time of frustration I am now mixing 50% coco into my ORGANIC soil mixes, and have found the issue to be gone. I also think that the 50/50 mix promotes stronger growth, and even faster bud development.

Regardless, when I left town and let my girlfriend and roommate handle the situation I came home to find my plants were stressing big time with some light green fringed leaves. I knew right away they had used tap water, but I confirmed with them what I already knew. I watered with adjusted water and things went back to normal.

Honestly without saying (cause I don't remember) who, there are lots of people on ICmag with some version of this problem I am sure from looking at photos.

I always appreciate hearing the basics again, and making sure Im following solid research and not just guessing.

[skullznroses]

So often I think the common diagnosis of a systemic and fundamental problem in grow set-up is for people to change nothing and just start dumping CalMag or SuCalMag or some other liquid lime type of product. Instead they are missing the fact that the problem is in the soil the roots are in, not with a lack of extra liquid nutrients. If you are using critical thinking so often the correct solution is to use less rather then use more growing products.

[LAMBS-BREAD]

To my understanding vermiculite increase N uptake capacity of the plant, while perlite fix the p and k in the soil, according to the man who sell me the worm casting. So maybe having a higher ratio of vermiculite than perlite in the veg mix, and vice versa in the bloom mix, will be more appropriated?

[mad librettist]

VG I would be very curious to see how old no till soil would handle your high pH water compared to fresh soilless mixes.

[VerdantGreen]

hi mad, from observation in my regular garden and others that i look after, when plants get tapwater rather than rainwater for a few weeks they mostly start to yellow. (and thats well kept no till organic soil)

[mad librettist]

Originally Posted by VerdantGreen

hi mad, from observation in my regular garden and others that i look after, when plants get tapwater rather than rainwater for a few weeks they mostly start to yellow. (and thats well kept no till organic soil)

the idea would be to test both side by side to see if there is a difference, even if it's only a few days.

then you could actually use pH readings of your soil in your tap water vs. distilled to work out the buffering potential of your soil.

[VerdantGreen]

im actually using rainwater for my whole grow this time and im trying to reduce the liming agents in the soil.. my plants have always done well anyway with amended tapwater but the soil isnt really re-usable and ive been wondering for a while if this is partly to do with the lime build up on top of the liming agents already in the soil.

i dont really believe in no-till for crops and bacterially dominated soil - and tbh i have doubts about re-using the same soil for the same crop over and over again - i prefer to use my spent weed soil in my veg garden where it is a valuable amendment for my clay soil, and i also use it re-amended to grow other crops like tomatoes.
if i had a bigger grow it might be different but the system works well for me atm.

VG

VG