Development and Harvest Yields of Greenhouse Tomatoes in Six Orgnaic Growing Systems

Dave Coulier · Feb 14, 2010

Im not sure what the size of the APB is in the Nursery Mix. Ill shoot them off an email tonight to find out. It does contain wetting agent, and dolomitic lime.

Is WFP, Water Filled Porosity. Im not sure Ive seen the acronym WFP before, so I want to make sure Ive got it right.

Also can you explain Pore Tortuosity. Thats another first for me. If I tried to google it, Im likely to find something more complicated than what you can give me

Ill pick up some EWC eventually. Im wanting to use up all my compost first before I spend $20-$30 on some Wiggle Worms at the local hydro shop. Of course it couldn't hurt to use both together to form the 10% in the mixture.

Now what exactly is a decanted slurry?

secondtry · Feb 14, 2010

Hey there,

Yea WFP is water-filled porosity and it's the term most commonly used, not WHC. AP is sometimes AFP but that's redundant, so AP is better.

I will upload a good paper I have about pore tortuosity, but basically it's the arrangement of the pores, "tortuosity" means basically twisty/not aligned and for example can refer to the path a molecule of O2 must take to reach the media surface (for example). This is more of a concern with APB that is over 4 mm or 5 mm. I have read of examples where 6 mm bark increases tortuosity. Honestly I do not understand tortuosity well enough either at this point. I need to read up on it this week, but what I wrote sums it up well enough.

Here is an example:

An O2 molecule under a horizontally aligned 6 mm piece of bark at 5" depth in media has to travel further to reach the surface of media than a O2 molecule under a horizontally aligned 2 mm piece of bark at the same 5" depth in media. The former media has higher tortusoity because the O2 molecule has to travel further to reach the surface of the media than the O2 molecule under the 2mm piece of bark. Does that make sense?

Yea using 5% of each is a good idea, unless the compost is high quality/fresh, then I probably suggest you use all compost as 'bagged' commercial vermicast (aka vermicompost, EWC) is often less than ideal.

A slurry is just a mixture of OM (organic matter) like EWC in water, but it's a thick mixture. Not quite a LCE (Liquid Compost Extract). Simply mix OM with water and pour on top of media. Decant is just to let the bigger OM particulate settle to the bottom of the contienr, then pour off the thinner slurry leaving some of the OM behind. It isn't needed to decant the slurry, some people don't bother and suggest it's better to pour all the OM on the media. It's up to you, I like to decant to keep the top of them media free from OM buildup.

Oh yea, look for a thread in this form about misting the media surface; that's good going info from people. I am going to try putting cheesechloth over the top of my media to help keep the moisture content more even throughout.

GL

secondtry · Feb 14, 2010

A few quick thoughts:

I think I read porometer data on the Fafard Nursery mix you are referring to. Let me see if I can find that for you, but it will take me until tomorrow, Im about to watch Terminator 4!

That mix you have come up should be great, really. I too am going to use a very similar blend with the same Fafard Nursery mix as a base so I can have a mix to suggest to people who don't want to or can't build there own soilless mix by screening APBF, etc. I am very interested to hear of your experience, please keep me informed thanks. I would be willing to split the cost of a porometer test of your media with you.

If you find TP, AP and WHC (ie., WFP) with the method from the link I would also like to read that data please. I can show you how to find bulk density too but it takes a good bit of media, about 5 gallons. I have sent media samples to labs for assays, it's cheap and sure informative like EC, elements, CEC, BD, etc.

I would suggest you check the pH of the Fafard Nursery mix when you first get it, and the EC too. I would appreciate it if you would do so and let me know what it is. You could use the "PourThru" method super easy and all it takes is a pH pen and a TDS or EC pen. If you are unfamiliar with the PourThru technique let me know and I can give you great PDFs on how-to with pics.

All the best.

Dave Coulier · Feb 14, 2010

Your definition of tortuosity made perfect sense. Ill still read the paper when you can supply the link though.

Ive already read the thread about the misting of the soil surface

Regarding the decanted slurry. It sounds like your top dressing with it if Im understanding correctly, but leaving less OM. I planned on mixing it right into the mix. Im hoping at 10% it wont impede drainage/aeration any significant amount. I guess if you topdress it, then you dont need to worry about it becoming an issue. Ive never done any top-dressing. Will the plant get the same benefit of top-dressing versus mixing it in the soil?

It'll be awhile before I can find out all the characteristics of the soil. I need to pick up the Nursery Mix on monday, then I still need to wait on my scale to come in the mail, plus my azomite thats coming as well.

Im using 1 tblspoon/gallon. I see your using it as well. 1tbls/gallon seems to be the most common amount used, but I know quite a bit more can be used with out any problems. What do you think is the ideal amount?

I wont be able to test EC since I dont have an EC meter. My ph meter is fucked up too. Ive bought a Milwaukee, and Hanna economy model, and both went kaput within 40 days. I still need to mail my Hanna one back for replacement. Ill get that done monday, and hopefully in two weeks Ill be able to test the PH, AP, TP, and WFP.

Also, Fafard does soil testing, water testing, fert testing, etc. They also offer it at a discount for Fafard customers, so Im gonna write them and see if they can do porosity testing as well.

Since I can't find a 1/16th sieve anywhere, I was thinking of buying these mesh screens and making my own sieve. The sizes look to be pretty good to get particles between 1/16th to 1/8th. Make sure to look at the picture of the screen.

http://www.mcnichols.com/ecommerce/...n=e16s1&page=itemDetail&itemNumber=3316113610

http://www.mcnichols.com/ecommerce/...n=e17s1&page=itemDetail&itemNumber=3408173610

big ballin 88 · Feb 14, 2010

i know this is a little bit late but on the first page you mentioned hydrating brewers grains. When i used to cultivate mushrooms, brewers grains and even moisture absorption is key to getting good even growth with no nasties. What i am getting at is we used a little bit of gypsum and jet dry when letting the grains sit in the water before pressure cooking. This was the biggest difference in my methods as the grains stop sticking, blowing up and in general just absorbed the water very well. Just a thought.

VerdantGreen · Feb 14, 2010

'aged pine bark fines'

im in UK and never seen this - is it what we would call 'composted bark'

Dave Coulier · Feb 14, 2010

VerdantGreen said:
'aged pine bark fines'

im in UK and never seen this - is it what we would call 'composted bark'

I would consider aged as partially composted. Composted would likely give us too many finely sized particles.

GorillaGrower · Feb 14, 2010

cool thread thank you for the info.. definetly waiting on the white paper you write up. are you goign to offer that to the community here?

also I got to say I love the use of acronyms in this thread! I have no idea what you guys are saying exactly.. but i love it.. new info to learn!

VerdantGreen · Feb 14, 2010

Dave Coulier said:
I would consider aged as partially composted. Composted would likely give us too many finely sized particles.

right, thanks
i really dont rate the composted bark you get here in the UK - perhaps the fine particles are why - it's far too wet.

call me old fashioned but i like a bit of soil in my soil. tomatoes taste much better when grown with soil in the potting mix rather than just soilless components - from my experience anyway

- and weed tastes better with some soil too imo.
V.

secondtry · Feb 14, 2010

Dave Coulier said:
Regarding the decanted slurry. It sounds like your top dressing with it if Im understanding correctly, but leaving less OM. I planned on mixing it right into the mix. Im hoping at 10% it wont impede drainage/aeration any significant amount.

You should be fine. I thought you were not going to include it in the mix.

If you read the paper in the first post the researchers used the same mix you are using, to it they added 15% EWC, more surfactant and lime.

Oh wait, they are using the Fafard's 'Special Organic mix' below. The addition of verm and perlite are not needed and not wise (perlite 'floats'), I assume the APBF make up less % of the mix than in your Nursery mix. I like your Nursury Mix better. And because your adding Azomite you are offering what gyspum does and more (tho less quantities of Ca and S, but that's fine).

85 % Fafard’s Special Organic Mix: Ingredients: Canadiansphagnum peat moss, vermiculite, perlite, gypsum, dolomitic lime, pine bark

15 % Vermicycle (commercial worm compost from Florida)

Here is another study which seems to be a replication of the one on the first post:
(it's an HTML page so I'll just like to it)

"ORGANIC GREENHOUSE VEGETABLE PRODUCTION"
J. A. Miles and M.M. Peet, Department of Horticultural Science
http://www.ces.ncsu.edu/depts/hort/greenhouse_veg/topics/organic-production-article.htm

I guess if you topdress it, then you dont need to worry about it becoming an issue. Ive never done any top-dressing. Will the plant get the same benefit of top-dressing versus mixing it in the soil?

Yes and no, it depends upon the situation and the goals of the application of OM. But in this instance yea the plant and soil food web should still benefit, tho mixing into media is better IMO. It's mostly for the PGRs (Plant Growth Regulators), microbes, etc.

It'll be awhile before I can find out all the characteristics of the soil. I need to pick up the Nursery Mix on monday, then I still need to wait on my scale to come in the mail, plus my azomite thats coming as well.

No worries. I'll be testing it soon, by next month or so. But we should compare data and hopefully they match. Can you test the vanilla Nursery Mix and your final mix?

Im using 1 tblspoon/gallon. I see your using it as well. 1tbls/gallon seems to be the most common amount used, but I know quite a bit more can be used with out any problems. What do you think is the ideal amount?

4-6% by dry weight; much more than 1 tbl/gallon. It has Ca, K, P, and lots of micronutrients.

I would also suggest you add zeolite powder to your mix if you can find it, it's cheap but is useful to increase CEC and the clay forms a bond with humus and Ca making aggregates in media. I also add colloidal phosphate powder to my mix. Get the smallest screen size you can, i.e., micronized is best.

I wont be able to test EC since I dont have an EC meter. My ph meter is fucked up too. Ive bought a Milwaukee, and Hanna economy model, and both went kaput within 40 days. I still need to mail my Hanna one back for replacement. Ill get that done monday, and hopefully in two weeks Ill be able to test the PH, AP, TP, and WFP.

Cool.

Also, Fafard does soil testing, water testing, fert testing, etc. They also offer it at a discount for Fafard customers, so Im gonna write them and see if they can do porosity testing as well.

Good idea. However, send samples to an independent lab might be a better choice, and just as inexpensive because state and University run labs are pretty cheap...

Since I can't find a 1/16th sieve anywhere, I was thinking of buying these mesh screens and making my own sieve. The sizes look to be pretty good to get particles between 1/16th to 1/8th. Make sure to look at the picture of the screen.

http://www.mcnichols.com/ecommerce/...n=e16s1&page=itemDetail&itemNumber=3316113610

http://www.mcnichols.com/ecommerce/eos/itemDetail?e1xecution=e17s1&page=itemDetail&itemNumber=3408173610

I wouldn't get those two screens. Ideal particle size for APBF is 2 mm to 4 mm to reach the media porosities I listed. Smaller than 2 mm is Ok but screening with a 2mm screen is a good idea. Over 4 mm is worse than under 2 mm.

The smaller opening size screen is 1.3 mm and the larger opening size is 2.7 mm.

Check out these two screens, the smaller is 1.9 mm and the lager is 3.3 mm. There is an even larger size at 5.1 mm but I think using the 3.3 mm screen is a good idea, more water retention:

1.9 mm (0.075") opening:
http://www.mcnichols.com/ecommerce/...Detail&itemNumber=3310253610&navCode=cc:sqmsh

3.3 mm (.1317") opening:
http://www.mcnichols.com/ecommerce/...54810&navCode=cc:sqmsh&navCode=avc:galvanized

HTH

secondtry · Feb 14, 2010

big ballin 88 said:
i know this is a little bit late but on the first page you mentioned hydrating brewers grains. When i used to cultivate mushrooms, brewers grains and even moisture absorption is key to getting good even growth with no nasties. What i am getting at is we used a little bit of gypsum and jet dry when letting the grains sit in the water before pressure cooking. This was the biggest difference in my methods as the grains stop sticking, blowing up and in general just absorbed the water very well. Just a thought.

Heyi BB88,

Thanks for the suggestions, but I was using wet spent brewers grains (similar to mash) as a source of N and easy to use (bio-available) C for composting. They are too moist when I pick them up so I was messing around with drying them out. Now I just use them as is and make sure the other compost feedstocks are low enough moisture content that when mixed with the wet spent brews grains the final pile will be 55-65% moisture content.

Thanks

secondtry · Feb 14, 2010

Hey there V,

VerdantGreen said:
'aged pine bark fines'

im in UK and never seen this - is it what we would call 'composted bark'

No, not generally, tho they can be mislabeled as composted, but there should be not be composting taking place (no addition of N, other OM or other composting requirements), only aging in a big pile. If you use pine bark (and some other softwoods) then you don't have to let them age, there should be not concern of phytotoxicity. Aging them makes them hold more water and a greater % of available water within that water. Aging is preferred for sure but not needed.

Fines are just small bark and shreds. They are sold as soil conditioner pretty often over here, maybe look for that?

HTH

secondtry · Feb 14, 2010

Hey there GG:

GorillaGrower said:
cool thread thank you for the info.. definetly waiting on the white paper you write up. are you goign to offer that to the community here?

Sure, but it will take longer than I thought, maybe a another month. Here is an edited excerpt from a (working) paper I have been writing for some time:

(to all: this is info is copy-written by me, do not re-distribute this info in a non-free platform (e.g., a book, magazine, etc)

"Soil Science Multi-Disciplinary Integration: Review, Identification and Development of an Ideal Substrate for Higher Plants and SFW"
---------------------------------------------------------

(WORKING PAPER)
Gojo, 2010

Abstract:

When attempting to design an ideal soil-less media for both crop plants and the soil food web there are many complicated multi-disciplinary soil science variables to consider. Further complicating the process is the disjointed nature of various soil science disciplines, where generally each discipline seems to act as an island unto itself. In this paper I attempt to explain each disciplines' import to understanding soil-less media properties and how they effect each other, the roots and rhizosphere and the soil microflora (i.e. bacteria and fungi), soil microfauna (i.e. protozoa) and soil mesofauna (e.g. nematodes); i.e. the soil food web. I attempt to standardize and update definitions for necessary qualifications and quantitations of soil and soil-less media with current understanding and agreements of soil physicists, chemists and microbiologists. Minimal, ideal and maximal benchmarks for soil-less media properties are presented and derived in part from said scientists' work and from typical properties (Melent’ev, et al, 1999) of chernozem (a Russian word meaning “black earth” describing a dark colored humus rich soil). New equations are proposed to further quantitate non-unavailable water into factions at initial container capacity (CC) comprising available water (AW, i.e. 1 – 30 kPa) and buffer water (BW, i.e. 30 – 1,500 kPa). An ideal soil-less media mixture and container height is proposed along with a new method for accurate water application regimes dependent upon total soil-less moisture content (MC) by wet weight gravimetric basis. Achieving ideal soil-less media benchmarks in terms of soil food web means for example, increased or ideal microbiological respiration, solublization of organic matter (e.g. nitrogen mineralization), along with microfauna and mesofauna grazing and feeding. Achieving ideal soil-less media benchmarks for roots means for example, increased or ideal photosynthetic rate (PN), daily net photosynthetic rate (PNnet), transpiration in relation to air humidity, respiration, root exudate (i.e. organic compounds) production and release, and greater intimate contact of roots-rhizosphere to available water held in pore spaces between media particles.

Soil-less Substrate Benchmarks:

TP = ≥ 70-85%
AS = 15 – 35%
AW = ≥ 20%
BW = ≤ 30%
UW = < 50%
tABW = ≥ 50%
CC = 60 – 65%
MCmin = 45 – 50%
HI = ≥ 0.9
BD = 0.15 – 0.3 g/cm3
Temperature = 20 – 24 °C
Container height = 30 - 45 cm
kPa at CC for plants = 1 – 10
kPa at CC for microorganisms = 10 – 15
pHw = 5.5 – 6.5
EC = < 0.5
P2O5 = 0.15%
CaO2 = 0.049%
MgO2 = 0.012%
Total Nitrogen = 0.61%
MOM = 5 – 10%
CEC = 15 – ≥ 30 meq/100 g
Luebke Humus Score = 10 – ≥ 30
Carbon to Nitrogen ratio = > 10 – 15

---------------------------------------------------------------------

GG wrote:
also I got to say I love the use of acronyms in this thread! I have no idea what you guys are saying exactly.. but i love it.. new info to learn!

Ha, you welcome. Here is the definitions to acronyms form my working paper. There could be errors and typos, but like I said it's a working version.

Here is an edited excerpt from a (working) paper I have been writing for some time:
(to all: this is info is copy-written by me, do not re-distribute this info in a non-free platform (e.g., a book, magazine, etc)

[FONT=Times New Roman, serif]Acronyms taken from:[/FONT]

[FONT=Times New Roman, serif]William C. Fonteno[/FONT]
“[FONT=Times New Roman, serif]Problems & Considerations in Determining Physical Properties of Horticultural Substrates”[/FONT]

[FONT=Times New Roman, serif]Fonteno, et al.[/FONT]
“[FONT=Times New Roman, serif]Procedures for Determining Physical Properties of Horticultural Substrates Using the NCSU Porometer”[/FONT]

[FONT=Times New Roman, serif]Drzal, et al.[/FONT]
“[FONT=Times New Roman, serif]Pore Fraction Analysis: A New Tool for Substrate Testing” [/FONT]

[FONT=Times New Roman, serif]Gojo, a.k.a, Ganja Din, a.ka., Secondtry[/FONT]
“[FONT=Times New Roman, serif]Soil Science Multi-Disciplinary Integration: Review, Identification and Development of an Ideal Substrate for Higher Plants and SFW”[/FONT]

[FONT=Times New Roman, serif]MC = “Moisture Content”, reported as a wet weight gravimetric unit, not volumetric, defined as WFP and used for CC, PWP, etc.[/FONT][FONT=Times New Roman, serif]

[/FONT] [FONT=Times New Roman, serif]TP = “Total Porosity”, the sum of water filled and air filled porosity, dependent upon bulk density.[/FONT]
[FONT=Times New Roman, serif]

[/FONT] [FONT=Times New Roman, serif]CC = “Container Capacity”, reported as moisture content by % wet weight (gravimetric basis). Known as “field capacity” for soil, that is, the MC of media after saturation and natural drainage of water from large pores.[/FONT][FONT=Times New Roman, serif]

[/FONT] [FONT=Times New Roman, serif]AS = “Air Space” (aka AP, “Air Porosity”) , the pores filled with air. According to Cornell U. if a media has less than 12% AS the plant will be hindered. For example, with TP at 50% the CC which will anaerobically hinder plants (calculated from 12% AS) is 38%. Both coco-coir and peat mixes have AS at or below 12%. Other reserachers (cite anmes) find 10% AS to be the the lowest limit. Pores lager than 416 microns are “macropores” and hold mostly air. AP is found as TP – CC.

[/FONT][FONT=Times New Roman, serif]
[/FONT] [FONT=Times New Roman, serif]BD = “Bulk Destiny”, as g/cm^3 and is dependent upon TP.[/FONT][FONT=Times New Roman, serif]

[/FONT] [FONT=Times New Roman, serif]WS = “Water Space” (aka WFP, “Water Filled Porosity” and WHC, “Water Holding Capacity”), pores filled with water are known as “capillary” pores and range from ≈ 416 to < 0.1 micron and have a water tension of 1 to > 1,500 kPa.[/FONT]
[FONT=Times New Roman, serif]

[/FONT] [FONT=Times New Roman, serif]AW = “Available Water” (aka, AWC, “AW Content”), water the plant can easily use and is less in quantity than AW for microbes. Pore range is ≈ 416 to 10 microns and water tension is 1-30 kPa. These pores are termed “mesopores” and hold water easily available to the roots. Traditionally AW is defined as 1-1,500 kPa and is found as so: CC - PWP; however, I propose we define AW as 1-30 kPa and calculate said AW as I describe below.[/FONT]
[FONT=Times New Roman, serif]

[/FONT] [FONT=Times New Roman, serif]BW = “Buffer Water”, plants can use water within this water tension range although it requires them to work harder for it and they do so under water stress. Pore range is 10-0.2 microns and water tension is about 30-1,500 kPa. These pores are termed “micropores” and hold water easily available to microbes, but not to plants. Traditionally there is no quantitation of BW, only AW as 1-1,500 kPa, thus I propose we define BW as 30-1,500 kPa and calculate said BW as I describe below.[/FONT]
[FONT=Times New Roman, serif]

[/FONT] [FONT=Times New Roman, serif]tABW = “Total Available and Buffer Water”, the sum of AW and BW and can be found by CC – PWP; traditionally defined as AW (1-1,500 kPa)[/FONT]
[FONT=Times New Roman, serif]

[/FONT] [FONT=Times New Roman, serif]UW = “Unavailable Water”, that which is not available to the plant. Pore range is < 0.2 microns and the water tension of > 1,500 kPa. These pores are termed “ultramicropores”.[/FONT]
[FONT=Times New Roman, serif]

[/FONT] [FONT=Times New Roman, serif]HI = “Hydration Index”, the value given to media that reflects the wettability of media. A higher figure means easier wettability. HI compares initial wettability with CC. An HI value of ≥ 0.80 means that the soil-less media should (re)hydrate sufficiently. Media with surfactant generally have high HI of > 0.90.[/FONT]
[FONT=Times New Roman, serif]

[/FONT] [FONT=Times New Roman, serif]MW = “Mass Wetness”, the weight of water per weight of media on a gravimetric dry-weight basis (g/g)[/FONT]

[FONT=Times New Roman, serif]PAP[FONT=Times New Roman, serif] = “Persistent [/FONT][FONT=Times New Roman, serif]A[/FONT][FONT=Times New Roman, serif]nhydrobiotic Point”, the point at which activity of most bacteria, protozoa and nematodes ceases and the microbes enter a state of anhydrobiosis due to excessive water tension. It is defined as media at 1,500 kPa (e.g. 1.5 MPa).[/FONT][/FONT]

[FONT=Times New Roman, serif]FPAP = “Fungi Persistent Anhydrobiotic Point”, the point at which activity of most fungi ceases and the microbes enter a state of anhydrobiosis due to excessive water tension. It is defined as media at 6,000 to 8,000 kPa (e.g. 6 – 8 MPa).[/FONT]

[FONT=Times New Roman, serif]PWP = “Persistent Wilting Point”, the MC at which plant growth is not supported, when the plant will always wilt. It is defined as MC at 1,500 kPa.[/FONT]

[FONT=Times New Roman, serif]MCmin = The MC at which plant and most soil food web functions being to be hindered, along with reducing the rewettability of some medias such as APBF and peat.[/FONT]

[FONT=Times New Roman, serif]MOM = “Media Organic Matter”, the fraction of soil-less media that is organic matter (OM).[/FONT]

[FONT=Times New Roman, serif]EC = “Electrical Conductivity”, the relative amount of ions in a solution or slurry.[/FONT]

[FONT=Times New Roman, serif]pHw = The pH score for media.[/FONT]

[FONT=Times New Roman, serif][/FONT]

secondtry · Feb 14, 2010

Hey there VG,

VerdantGreen said:
right, thanks
i really dont rate the composted bark you get here in the UK - perhaps the fine particles are why - it's far too wet.

Yea that sounds like composted with addition of OM, etc. Not what you would want. I am sure they have bark fines there, they don't have to be pine but softwood is generally a better choice than hardwood (which have to be aged).

call me old fashioned but i like a bit of soil in my soil.

But what is "soil"? It's mostly clay and inorganic particles. What makes soil, well, "soil" is the humus fraction and the % OM. Healthy, alive, humus rich soil (e.g., chernozem) should have at least 5% OM, more is better but that is a good benchmark. The soilless mix I suggest has over 5% OM, near 10% OM, I need to find the OM (via. ashing) and I will do that next month (it's easy to do at home). The OM is necessary to have soil that is truly alive and high function soil food web. The mix DC is going to use should have sufficient OM at 10% compost and 5% EWC. The humus fraction of soilless media (ie. Luebke Humus Score in my last post) can be increased with addition of high CEC clay, humic acid and Ca helps too, that is why I suggest zeolite powder, humic acid and azomite be added to all soilless mediums.

tomatoes taste much better when grown with soil in the potting mix rather than just soilless components - from my experience anyway - and weed tastes better with some soil too imo.
V.

Agreed, well kind of, see my previous comments above.

All the best

Dave Coulier · Feb 14, 2010

secondtry said:
I would also suggest you add zeolite powder to your mix if you can find it, it's cheap but is useful to increase CEC and the clay forms a bond with humus and Ca making aggregates in media.

I know you've read about bulk density affecting CEC in container media, so Im guessing you read this article by Bill Argo & Paul Fisher. This article is part of a yearly series. Theres good stuff in there, so everyone read the rest.

http://www.greenhousegrower.com/magazine/?storyid=47

Ive looked into Zeolite before, and find it interesting. Im guessing it has a high bulk density, which is why you include it still?

Which brand of Zeolite do you use?

secondtry said:
I wouldn't get those two screens. Ideal particle size for APBF is 2 mm to 4 mm to reach the media porosities I listed. Smaller than 2 mm is Ok but screening with a 2mm screen is a good idea. Over 4 mm is worse than under 2 mm.

The smaller opening size screen is 1.3 mm and the larger opening size is 2.7 mm.

Check out these two screens, the smaller is 1.9 mm and the lager is 3.3 mm. There is an even larger size at 5.1 mm but I think using the 3.3 mm screen is a good idea, more water retention:

1.9 mm (0.075") opening:
http://www.mcnichols.com/ecommerce/...Detail&itemNumber=3310253610&navCode=cc:sqmsh

3.3 mm (.1317") opening:
http://www.mcnichols.com/ecommerce/...54810&navCode=cc:sqmsh&navCode=avc:galvanized

HTH

I was basing my screen size off the dimensions Al suggests. 1/16th to 1/8th. You are suggesting 1/13th to about 1/6th. I can understand the larger size for better drainage, but is that the only reason? I know Al says if all particles were 1/8th there would be no perched water table, so 1/6th would be even better no doubt.

Theres another site Ive got open that has mesh screens too. Ill check them out for the 2-4mm and throw up up here, and see what you think.

Thanks.

*Edit: Here is the link

http://www.mcmaster.com/#9219t158/=5thlko

They have a perfect mesh for the 2mm, but unfortunately the closest they have to 4mm is 3.5. I dont want to order from two sites(shipping charges). They also sell 12"x12" sheets, so I probably save some money on them not having to cut to the size I need.

secondtry · Feb 14, 2010

Hey,

Dave Coulier said:
I know you've read about bulk density affecting CEC in container media, so Im guessing you read this article by Bill Argo & Paul Fisher. This article is part of a yearly series. Theres good stuff in there, so everyone read the rest.

http://www.greenhousegrower.com/magazine/?storyid=47

Yea their work is not valid when one incersaes BD with compost, EWC, etc. As they noted, liming increase CEC, as does addition of humic acid/creation of humus aggregate in soilless media. It's funny you link to that report, a friend of mine asked me to critique it a few weeks ago via. email. I think it was a valid and good critique of that report and if you would like to read it I can post it here.

Ive looked into Zeolite before, and find it interesting. Im guessing it has a high bulk density, which is why you include it still?

Yea the BD is good, but only a little (relatively) is added. The CEC is why it's added, and to help form the Ca-clay-humus aggragate. The CEC of zeiolite powder is 100-200 meq/liter, that's a lot considering soil CEC is around 6-10.

By adding both high BD items like compost and EWC, lime and humic acid, along with high CEC items like zeolite and compost the work by Argo and Fisher is no longer valid. Also, microbes like bacteria are mobile CEC bags, they hold ions until eaten by protozoa (for example) which release held ions, ie. N, some of which are absorbed by the roots.

Which brand of Zeolite do you use?

From a company in Vermont, let me try to find the info. I'll be back.

I was basing my screen size off the dimensions Al suggests. 1/16th to 1/8th. You are suggesting 1/13th to about 1/6th. I can understand the larger size for better drainage, but is that the only reason?

The sizes I suggest offer increased AP, AW and BW, and lower pore tortosity. I have studies where different size ranges of bark was uses: < 2mm, 2-4 mm and 4-6mm; in all studies the 2-4mm had the best properties. But I am sure the 1/16th to 1/8th inch size will provide good results too.

I know Al says if all particles were 1/8th there would be no perched water table, so 1/6th would be even better no doubt.

That is not correct to my understating. There will always be a perched water table.

Theres another site Ive got open that has mesh screens too. Ill check them out for the 2-4mm and throw up up here, and see what you think.

Thanks.

NP.

secondtry · Feb 14, 2010

They have a perfect mesh for the 2mm, but unfortunately the closest they have to 4mm is 3.5. I dont want to order from two sites(shipping charges). They also sell 12"x12" sheets, so I probably save some money on them not having to cut to the size I need.

I would suggest getting the 3.5mm because the biggest open size I found for you was 3.3 mm. I am confused tho, are not all the screens from McMaster?

Dave Coulier · Feb 14, 2010

Here is a quote from Als 5-1-1 thread.

I grow in highly-aerated soils with the bulk of the particles in the 1/16"-1/8" size, heavily favoring the larger particles, because we know that perched water levels decrease as particle size increases, until finally, as particle size reaches just under 1/8" the perched water table disappears entirely.

Theres actually two sites I was checking out screens from. One is mcmaster, the other is mcnichols. All those mc's are confusing

Go ahead and throw up that critique. Ill read it.

secondtry · Feb 15, 2010

Hey Dave,

Dave Coulier said:
Here is a quote from Als 5-1-1 thread.

I grow in highly-aerated soils with the bulk of the particles in the 1/16"-1/8" size, heavily favoring the larger particles, because we know that perched water levels decrease as particle size increases, until finally, as particle size reaches just under 1/8" the perched water table disappears entirely.

Yea I think that is not correct. See the Cornell U., site "Media: Rooted in Success". But I could be wrong, I will look into it.

]Theres actually two sites I was checking out screens from. One is mcmaster, the other is mcnichols. All those mc's are confusing

Ha, ok.

Go ahead and throw up that critique. Ill read it.

OK, give me a few minutes. But I totally agree, that is a great series by Argo, et al., tho not all of the articles are relevant to organic microbioloigcal horticulture.

Matt Taylor and Dieter Lohr (Jan, 2010) wrote another article in that series about controlling media pH with the use of different N: ammonium (cation; acidic) and nitrate (anion; alkaline). And they proposed that trying to adjust media pH (via. lime) is kind of futile considering the N can swing the pH from (IIRC) 0.2-0.6 points pH. However, in organics the interaction of microbes, roots and ammonium means the pH of media actually increases, which is why the pH issues Taylor, et al., wrote about are not of concern with microbiological horticulture (please see page 3, paragraph 3 and 4 of the paper i the first post for very good detailed explanation of this phenomenon).

Problem being plants like cannabis like nitrates, not ammonium. Also, IIRC most 'organics in a bottle' (e.g., EJ) have higher % of ammonium comprising N verses nitrate (tho I have to check my notes to be sure that is accurate claim).

Ill post the short and simple critique I wrote about the Argo, et al., CEC info soon.

All the best. I am very impressed at your level of knowledge.

secondtry · Feb 15, 2010

Here is the link about pH and ammonium vs. nitrate:

(very important read for conventional growers)

Addressing pH Problems
Fine-tuning your substrate pH is all about the nitrogen. If you control it, you’re in control.
By Matt Taylor and Dieter Lohr
January 2010
http://www.greenhousegrower.com/magazine/?storyid=2890

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