passive plant killer

[village green]

Yes, that sounds about right. The containers are sloped inwards towards the bottom so maybe just slightly less. Luckily (or not so luckily as things might be) this round has been delayed, so the plants I'm using will have been vegging for more like 12 weeks by the time they are flipped. But since there is a separate veg setup, and I'm going for 4 trees in a 5 bulb diamond room, 8 weeks may be a good length of time for turnover in the long run.

One of the reasons I went with the totes is for the lower profile, I wanted to do 3.5 gal buckets but the height was just too much for the space I'm working with. I'm curious to see how the ppks will do in a KBS/heath style room. Any one of you talented growers in here can and have pushed the idea much further, but I'm still stoked to give it a go

When you cite your veg times are you talking about time from when the plant is a rooted clone to flipping, or do you mean 8 weeks time vegging in the flowering room before flip? I'm asking because I noticed in your wicked pulse thread you have vegged the plants in place to fill out the screen.

Hey Real Ting
Are you stacking one tote in another? If so, how many inches of air gap does that give you?
I think veg time just refers to your light schedule, not the room you use to impose it.

 

[real ting]

Hey Real Ting
Are you stacking one tote in another? If so, how many inches of air gap does that give you?
I think veg time just refers to your light schedule, not the room you use to impose it.

The totes are stacked with a lid on the bottom tote, with 2 2.5" holes cut out for the media wicks. They end up just around 17" tall. They have the same 6" sink tailpieces, tire valve fittings, pulse terminals (2 per tub) and reservoir setup as detailed in d9s wicked pulse thread. I will probably run the airgap around 3", the level is adjustable with a float valve installed inside a smaller Tupperware in the control reservoir.

 

[mcfly420]

Since total media porosity has been shown to be ~74%, 50% of which (37%) inter-aggregate macropores, this result suggests that plant-available water is only found in the inter-aggregate macropores, with minimal micropore water plant-available.

the above pics/text was from the leachate paper, this is from the physical/hydraulic properties of ceramic media

top one uses meters btw
for 1-2mm at -10cm(0.1m) the water content is 37% because the larger pores have been drained.

Matric potentials of 0 to 10 cm are far below the permanent wilting point (-1.5 MPa or -15,000 cm) at which plants cannot extract water.

at -15000cm, ~30% of the water remains in those micropores. Roots can redistribute water, but Ive still got issues with that. So that daily irrigation is providing all my plants water. The graphs helped because I dont want the pores completely saturated at low heights and yet some water should remain (above 37%) at my container height of 17cm. Also throwing some cuts in a 50-50mix by volume of the smaller and larger particles.

edit-

Hydraulic redistribution can only occur during the “dark” or “lights off” phase.

 

[zeke99]

5/16 ID tubing currently back ordered on 4fishin.com

PPK Nation!

 

[zeke99]

I just wanted to give a mention for Greentrees Hydroponics.

http://www.hydroponics.net/items/

I've purchased from their online store on numerous occasions. They always seem to have one of if not the best price, they never appear to be out of stock, they always ship right away and always pack the boxes tightly. It's very similar to USplastics in these factors...

 

[mcfly420]

Roots have developed components that greatly restrict the movement of water out into the soil, but the gates aren’t 100% effective, particularly among younger roots. If some roots are located in dry soil, and others in wet, the water in the roots’ xylem will be subjected to a pressure gradient. The drier soil will be using the xylem as a straw to suck moisture from the wetter soil. This is a purely hydraulic phenomenon, not biological. Water within the soil can thus be redistributed from wetter regions to drier, provided the pressure gradient is strong enough to overcome the resistance imposed by the xylem. This only occurs in times of water scarcity.

Meinzer - Hydraulic redistribution was possible once soil matric potential fell below approximately -0.2 to -0.4 MPa

I guess my point is only the micropores could create a strong enough pressure gradient and the larger pores which hold the vast majority of the PAW will remain empty

 

[mcfly420]

how far/fast water will travel/wick?
The hydraulic conductivity of a soil is a measure of the soil's ability to transmit water when submitted to a hydraulic gradient.
Profile and Turface

 

[mcfly420]

Water is not distributed evenly throughout the container. Adhesion, cohesion and capillary action attract water to particles and resist gravity. The ability of media to hold water through adhesion and cohesion is referred to as matric potential. Matric potential is the same throughout the container. Gravity pulls water down through the container and out of the drainage holes. While gravity is constant throughout the container, gravitational potential is greater at the top of the container and lower at the bottom. Because of this gradual decrease in gravitational potential toward the container bottom, matric potential is higher at the container bottom and media particles are able to hold more water. This causes a perched water table, or layer of saturation, at the container bottom.

The matric potential, ψm, is that portion of the total water potential associated with the more or less solid colloidal matrix of the system. This potential is one of the more interesting, particularly in the soil-water system where it has been given many names, including capillary potential, capillary head, suction head, tension head, and imbibitional pressure. It has been defined in the literature as both a negative pressure and a positive suction head. The matric potential includes the forces of adsorption at the soil-water interfaces and the forces caused by surface tension at the air-water interfaces. Free water has zero matric potential and will move into a dry soil because of these forces, so the matric potential is negative for an unsaturated soil, and zero for a saturated soil. Thus, the removal of water from a soil-water system decreases the matric potential of the water remaining in the system.

 

[mcfly420]

This helped me understand a few things and provided something to compare the calcined clay with

ABSTRACT. Physical characteristics of two media were studied concerning water availability to roots, as reflected in specific transpiration rate, stomatal conductance, and specific growth rate of very young leaflets of ‘Kardinal’ rose. Plants were grown in UC mix [42% composted fir bark, 33% peat, and 25% sand (by volume)] or in coconut coir. Water release curves of the media were developed and hydraulic conductivities were calculated. Irrigation pulses were actuated according to predetermined media moisture tensions. Transpiration rate of plants was measured gravimetrically using load cells. Specific transpiration rate (STR) was calculated from these data and leaf area. STR and stomatal conductance were also determined using a steady-state porometer. Specific growth rate (RSG) of young leaflets was calculated from the difference between metabolic heat rate and respiration rate, which served as an indicator for growth potential. Low STR values found at tensions between 0 and 1.5 kPa in UC mix suggest this medium has insufficient free air space for proper root activity within this range. Above 2.3 kPa, unsaturated hydraulic conductivity of UC mix was lower than that of coir, possibly lowering STR values of UC mix-grown plants. As a result of these two factors, STR of plants grown in coir was 20% to 30% higher than that of plants grown in UC mix. STR of coir-grown plants started to decline only at tensions around 4.5 kPa. Yield (number of flowers produced) by coir-grown plants was 19% higher than UC mix-grown plants. This study demonstrated the crucial role of reaching sufficient air-filled porosity in the medium shortly after irrigation. It also suggests that hydraulic conductivity is a more representative measure of water availability than tension.

Unlike in soil, matric potential (ψm) measured in porous media is usually quite low. Still, in many cases, water flux across the medium/root interface cannot match atmospheric demand for water, even under near-ideal aerial conditions. This is due to a sharp decrease in K with decreasing φ, typical of most substrates (da Silva et al., 1993). A relatively small decrease in φ (e.g., of 1% to 5%) may decrease K by an order of magnitude and thus greatly affect water availability to the roots (Wallach et al., 1992). This rate of decrease is much sharper than normally found in natural soils. Low K values indicate that the rhizoplane is exposed to tensions that are much higher than what can be measured in the bulk soil. da Silva et al. (1993) demonstrated that in substrates, the main limiting factor to water uptake is K and not ψm, as measured in the bulk solution. To make an informed choice of a growing medium, the relationship between φ and K should be known. Measuring K in situ in porous media is laborious and cannot be done under commercial conditions. However, Raviv et al. (1999) demonstrated that reliablemodels for K vs. φ and vs. ψm might be valuable for irrigation control. Growth rate is often reduced from the maximum obtainable or potential growth rate by water and other environmental stresses.

‘Kardinal’ rose grafted on Rosa canina ‘Natal Brier’ were planted in ten 5-L containers per medium, filled with either coconut coir(composed of shredded, partly composted coconut husk fibers) or a UC mix [42% composted fir bark, 33% peat and 25% sand (by volume)]. Within each treatment, the weights of three plants were logged at 15-min intervals using load cells (model SP4-30KG; HBM Co., Marlborough, Mass.). ψm of four plants per medium was also recorded at 15-min intervals, using tensiometers equipped with high-flow ceramic tips and electronic pressure transducers (model LT; 15 cm long, Irrometer Corp. Riverside, Calif.). In addition to recording moisture tensions, the tensiometers (inserted to a depth of 10 to 11 cm, 7 to 8 cm above the bottom of the container), were used to actuate an automated irrigation system based on tension setpoints. Usually, the setpoint for irrigation was 3 kPa. Twice a week, over the period April to July 1999, higher tension was applied to enable determination of specific transpiration rate (STR), stomatal conductance, and RSG, over a wider range of moisture conditions. The irrigation pulses were of adequate volume to allow some water to drain out of the containers, so as to prevent salinity buildup, mimicking the commercial practice aimed at discharging excess nonnutritional ions.

The moisture retention curves were able to represent the data of the two media well (Fig. 1A). Total porosity of the two media was 95.1% for coir and 76.0% for UC mix. At a tension of 1 kPa, 9.5% and 5.6% of the volume of the pores became air filled in coir and UC mix, respectively, suggesting better aeration conditions in the root zone near container capacity of coir-grown plants. At 10 kPa, the moisture retention curves were close to the asymptotic moisture content of 39.7% and 24.5% for Coir and UC mix, respectively. On the whole, coir had a higher total porosity and free air space than the UC mix. However, the available water capacities (as defined by Bunt, 1988) were identical: water contents between 1 and 10 kPa for both media were 46%. When free drainage following an irrigation event stopped (known as container capacity), the container bottom was at saturation (zero moisture tension) while tension near the container surface was about 1.8KPa since the depth of the medium was 18 cm. Since the tensiometer was located at a depth of 7 to 8 cm, its reading at this stage was ≈0.7 to 0.8 kPa. Corresponding volumetric air contents at the tensiometer tip were 3% for UC mix and 8% for coir. The former is considered to be an extremely low value

Hydraulic conductivity also varied with container depth. Hydraulic conductivity varied within this moisture tension range (and container depth) by about two orders of magnitude. This, coupled with the gravitropic growth habit of roots, were probably the causes for the common phenomenon of root mats near the bottom of the pot. In UC mix-grown plants, this dense root layer may be subjected to oxygen deficiency for a considerable length of time after an irrigation pulse. Suboptimal aeration decreases transpiration via its effect on root permeability and stomatal conductance. The fact that roots concentrate at the bottom in spite of the periodic events of oxygen deficiency in this region, suggests that water stress is more damaging to their development than oxygen deficiency.

The momentary hydraulic conductivity of the medium solution, together with the difference between the Ψm at the medium-root interface and in the medium bulk, are measures for the ability of water to flow from the medium to the root-medium interface. This water flux should replenish water being withdrawn by the roots. Thus, it is inevitable that at some level of dryness, hydraulic conductivity will restrict water supply to the roots to the extent that it will be insufficient to meet transpirational demand of the plant. For example, assuming peak transpiration per plant of 500 cm3·h–1 and a functional root surface area of 2000 cm2/plant, we can estimate that a minimal K of 0.25 cm·h–1 (or log10K(0.1) = –1) would be required to constantly satisfy the demand for water which the plant is experiencing. This K value corresponds to a tension of up to 3.3 kPa in UC mix and of 6.1 kPa in coir. This suggests that coir affords plants the ability to avoid water stress better than UC mix by allowing for faster water movement at higher tensions.

The high Ks of coir and its higher free air space at container capacity expose the roots of coir-grown plants to much shorter periods of oxygen deficiency than that of UC mix. Below 1.5 kPa, average STR values of plants grown in UC mix were much lower than those grown in coir (Fig. 2). STR of UC mix-grown plants also was lower than that of coir-grown plants in the range 1.5 to 2.3 kPa where K of coir was lower than that of UC mix. This may result from the following sequence of events. A short period of oxygen deficiency may occur at the end of each irrigation cycle. The water retention curves (Fig. 1A) of the media suggest a longer period of oxygen deficiency for UC mix than for coir within the whole container volume. Furthermore, since the roots of both media are unevenly distributed within the container, with more roots located at the bottom than at the top, the root mat at the bottom may experience suboptimal aeration. This may happen while tension at the tensiometer tip, located at middepth and above the zone of saturation, is within the optimal range. This, again leads to higher oxygen deficiency in UC mix than in coir. The fact that roots formed mats at the bottom of the containers, where conditions of oxygen deficiency prevail, is apparently counter intuitive. This phenomenon may be a result of the gravitropic growth mode of roots and of the relatively greater negative impact caused to the roots by water shortage than by oxygen deficiency. Differences in plants response to moisture content in the two media, despite identical available water capacities, underscore the fact that horticulturally, this term is less relevant than moisture tension, hydraulic conductivity, and oxygen content.

The roles of free air space and hydraulic conductivity in determining the water status of the plant should be emphasized: free air space through its effect on oxygen availability to roots and hydraulic conductivity via its effect on water availability. A detailed study of physical and hydraulic characteristics of the media should be conducted whenever decisions are made regarding the suitability of media, so that the best choice of medium can be made and water availability can be optimized using control technology.

 

[mcfly420]

Cant find data on WHOLE parboiled rice hulls, only once theyve been grounded/screened, but the water within seems contained past -10cm h20 and releases while in the EAW range (under -5KPa?). For a passive wick PPK, a mix of well-rinsed/treated profile and turface may be the best clay only option. Set an air gap equal to the air entry point, around 2in, and 6in of medium in the bucket

There are two initial stages at which retention curves are measured: A drainage curve is obtained by establishing a series of equilibria by drainage from zero pressure head. A wetting curve is obtained by equilibrating samples wetted from a low water content or high suction. The retention curve is hysteretic, i.e. the water content at a given suction for a wetting substrate is less than that for a draining substrate (Wallach et al., 1992a). The drainage curve that starts on complete saturation of the substrate is called the initial drainage curve. The main wetting curve is obtained by wetting the substrate from low water content. As the substrate is wetted along the main wetting curve and the suction approaches zero, the water content approaches a value that is less than the TP, θs, due to the presence of entrapped air (.igure 4). This value is about 0.8θs to 0.9θs and is called the natural saturation of the satiated water content (Klute, 1986). The drainage curve starting at natural saturation is called the main drainage curve. The main drainage curve merges asymptotically with the initial drainage curve as the suction increases.

 

[delta9nxs]

Yes, that sounds about right. The containers are sloped inwards towards the bottom so maybe just slightly less. Luckily (or not so luckily as things might be) this round has been delayed, so the plants I'm using will have been vegging for more like 12 weeks by the time they are flipped. But since there is a separate veg setup, and I'm going for 4 trees in a 5 bulb diamond room, 8 weeks may be a good length of time for turnover in the long run.

One of the reasons I went with the totes is for the lower profile, I wanted to do 3.5 gal buckets but the height was just too much for the space I'm working with. I'm curious to see how the ppks will do in a KBS/heath style room. Any one of you talented growers in here can and have pushed the idea much further, but I'm still stoked to give it a go

When you cite your veg times are you talking about time from when the plant is a rooted clone to flipping, or do you mean 8 weeks time vegging in the flowering room before flip? I'm asking because I noticed in your wicked pulse thread you have vegged the plants in place to fill out the screen.

i hope you do a thread on this.

when i speak of veg times i am speaking of the time under the big lights. using a screen they have to be vegged in place.

with my perpetual set up i had a separate vegging area with a 1k and rotated plants into the flowering room.

 

[delta9nxs]

hey, mcfly! i see that you too are fascinated by the world of plant/soil/container hydraulics.

keep it up! i have read some of the papers you are posting from and try to read everything i see on the subjects.

i use turface and rice hulls now but still believe that almost anything with the right mechanical properties will work fine as long as it is not outright toxic.

 

[MedScientist]

HiYa!

I got tired of scooping out the perlite when washing the Turface, so I just use straight Turface now. Drains Fast, No Problems, Why not? Its much easier to clean between runs now!

 

[delta9nxs]

HiYa!

I got tired of scooping out the perlite when washing the Turface, so I just use straight Turface now. Drains Fast, No Problems, Why not? Its much easier to clean between runs now!

hey, welcome back, if you ever left! when using straight turface you might consider screening it through a regular mesh aluminum window screen to remove fines and give greater air porosity.

the turface mvp right out of the bag has less than 15% air porosity. by screening you can get it up to about 22-23 %.

i have found that, with a heavy pulse schedule, 30-35% is better.

if i went back to hand watering i would use it straight again but screened.

later, d9

 

[catman]

I got tired of scooping out the perlite when washing the Turface, so I just use straight Turface now. Drains Fast, No Problems, Why not? Its much easier to clean between runs now!

I fill a big rubbermaid tote full of turface and perlite. Then, top it off with water... mix it up a bit.. then I drain (siphon) the container and scoop all the perlite off the top. Repeat once or twice.

 

[DocCrow]

Mini SOG PPK

Mini SOG PPK

Delta9nxs,

I was directed over this way by Oldone. This is one of the best threads I have found on here. This should work well for me, as it will seems to be one of the only ways I can leave my grow and actually go on vacation, etc.
This is what I have come up with to adapt your system to my wants and needs. It is designed to fit perfectly into my cabinet that I am building right now. The theory is to grow 36 18" lollypopped plants SOG style. 4 in and 4 out every week harvested perpetually. My containers will hold 32 oz of coco, and I plan on following your/Oldone's feeding schedule of Jacks and CalNit. I think I can yield an average of 7 grams per cut. This should supply me and my wife with ~1 oz per week. I plan on keeping 4-5 mothers for variety, and this, as opposed to a SCROG will allow me to grow a greater variety, as I can get tired of smoking the same strain all of the time.

Here is my design


It will hold 6.5 gallons, allowing for a 3" Airgap. I plan on pulse feeding ~32oz 1 time per day to keep the salt from building up in the top.

How well do you think this will work?

with this many small plants (should be 18" tall) 6.5 gallons in the tank, and 10 gal in the bulk reservoir how do you think this will go between top-offs?

am I f***ing crazy?

Thanks for all of the info and the help you have given everyone. I am still trying to read through this whole monster thread so forgive me if you have addressed any of this before.

Everyone please feel free to chime in with comments/critiques. I want to get this right the first time, and where I am building the reservoir from scratch to get it sized perfectly for my space I don't want to have to do it twice.

DocCrow

 

[gregor_mendel]

DocCrow:

I like it! What light do you plan to use for this?

I am working through similar idea now, as I may soon move to a non-med state, and have a much smaller show.

Is the box you show based on something that Stewe sells, or are you building that?

 

[DocCrow]

Gregor

It is going in a 2.65 sq' box lighted with 8 42w cfl that will be sealed off and separately vented. The box is a storage cabinet you can see the build thread in my sig. 8 42w cfls will give me 7000-7500 lumens per sq'.

the box is something I will build myself, as it need to be sized to fit my cabinet and make the best use of the room. I am trying to figure out the construction now. HDPE sheets would be the best but are $$, so I will probably build it out of plywood and waterproof it with flex seal or epoxy paint. The flex seal sounds like the easiest way as it just sprays on, but I am worried about off gassing / toxicity in the nutrients. Anyone have any input on this?

 

[oldone]

I got an idea for you DC, but I'll post in your thread...

OO

 

[ImaginaryFriend]

I plan on pulse feeding ~32oz 1 time per day to keep the salt from building up in the top.

How well do you think this will work?

There is much more to the pulse than simply keeping salts in solution. I suggest pulsing much more often than once a day... Every fourty five minutes or so? More often? Less? But multiple cycles per day. In the twenties, or thirties. Not the ones. (My recommendation.)

allowing for a 3" Airgap

Shorter containers will run wetter. Keep in mind that the media will not have a uniform humidity, but will have a profile where it gets progressively drier as it approaches the surface. The taller the container, the more variety in humidity profile, the shorter the less.

with this many small plants (should be 18" tall) 6.5 gallons in the tank, and 10 gal in the bulk reservoir how do you think this will go between top-offs?

Long time, and you can always increase your bulk res size if you need to neglect your garden even longer than a long time.

am I f***ing crazy?

Yup. Must be. Hope so.

I think I can yield an average of 7 grams per cut.

You better. You better. You better.