[permaculture] [compost_tea] Dispensing tea - spray or dribble?

venaurafarm venaurafarm at bellsouth.net
Sat Mar 30 18:02:36 EDT 2013

>> On 3/28/2013 5:22 PM, bberryvp wrote:
>> I plan to apply bacterial tea to some pasture I am trying to improve.
>> I will probably make a dispenser for my tractor, since about 10 ft
>> wide is all I need. Rather than spray, one thought is to basically
>> dribble the  tea out of a manifold, with holes closely spaced such as
>> 1/2 inch apart. I can solve issues such as manifold pressure
>> distribution to keep it pretty even. Since the tea is basically an
>> inoculant (as I understand it), could it be that dribbling might be
>> equal or better than spraying, since when spraying most of it will
>> not make contact with soil.
> On 3/28/2013 9:41 PM, venaurafarm wrote:
> If you don't intend to do foliar spraying then dripping it onto the
> ground seems like a good idea, if you can control the distribution rate
> without clogging the system. Will it be gravity flow or pressurized
> lines? Beyond a certain point the microbes can be killed by being forced
> with the tea through a system that uses too much pressure.
> Here's a person who knows all about this and has designed and built a
> large truck-mounted spray rig with sensors and controls to prevent over
> pressurizing the lines: Frank Schultz

Frank sent me this reply:

Yes, you are quite correct: Microbes are fragile and easily destroyed by 
impact or crushing.

General Notes -

1.    Pumps - use only a diaphragm pump.  The lower the speed, the 
better.  Other types are very destructive.  Centrifugals are the worst 
(giving you “bug purée”).  Note that manufacturers of most diaphragm 
pumps specify a 50-mesh inlet screen to avoid clogging or blocking the 
valves.  Large diaphragm trash pumps require no screen (they’ll accept 
chunks up to several inches) - however, their output pressures tend to 
be very low (a few feet of head).

2.    Pressures - The lower the better.  25 psi max.  The problem is 
de-compression.  When suddenly released into the atmosphere at high 
pressures, the cell walls explode.  I use nozzles rated for 15 psi min 
(for proper spray pattern) and try to stay close to this pressure (just 
a little over 1 Atmosphere [Atm.]).  Do not use a pressure relief 
(pop-off) valve to regulate pressure - High velocities into right-angle 

3.    Piping - To keep fluid velocities low, I use piping larger than 
what would normally be recommended for the flow rate.  At turns, I try 
to use hose with wide, sweeping turns.  If an elbow or tee is required, 
I adapt up to the next larger size, then reduce back down.  If you’re 
using PVC piping, you can use Schedule 80 electrical (pulling) ells to 
also reduce the K-factor.  Even though they are not pressure rated, I’ve 
had no problems up to 100 psi.

Please do not dismiss the many benefits of foliar application.  While 
spraying is a completely different proposition from drip, foliar feeding 
can achieve the fastest response time from your plants - especially if 
there are disease issues or obvious nutritional problems.  Also, since 
we field (broadcast) spray here, most (80%) of the spray mix goes on the 
ground - and most of the other 20% then runs off the leaves - onto the 
ground.  Don’t limit yourself by thinking in terms of biology only.  We 
recommend the addition of blackstrap molasses, humate, seaweed, 
micronutrients, trace elements and other things to the mix (depending 
upon the deficiencies found).  These things are readily taken up through 
the leaves.  Note: Don’t overdo the molasses - 1 quart/acre max.

With a few exceptions, anything sprayed has to pass a 50-mesh screen. 
We design soil fertility and crop nutrition programs for [generally 
large] growers all over the world.  For irrigated growers, this involves 
a combination of spray and fertigation (through pivot or drip).  In 
addition to biology, we always recommend some combination of nutrients. 
  Some soil chemistries rapidly tie-up some of the nutrients - and in 
fact, the only way plants can get these nutrients for any length of 
time, is foliar.  Accordingly, when a plant shows deficiencies in some 
of these (particularly the micros and traces) the surest and fastest way 
to correct these is with foliar.  Be aware that many plant diseases are 
caused by nutritional deficiencies - especially in the micros/traces.

The really cool thing about irrigation is that you can continuously 
feed, giving your plants the nutrition they need (and only what they 
need) when they need it as their nutritional requirements change 
throughout the growing season.  Performance and quality results can be 
truly dramatic.  And - a nutritionally-balanced plant can require up to 
70% less water(!) (per university studies) - And a healthy plant is 
subject to fewer disease and insect pressures!

With respect to your drip (“dribble”) plan:  This involves a different 
set of problems.  Commercial drip tape usually operates in the 8 - 10 
psi range.  The total opening presented by the micro-emitters is 
calculated for a maximum run length given the diameter of the tape to 
ensure consistent flow from each of the emitters over the entire length 
(same flow out of the first emitter through to the last).  The 
electrical equivalent is presenting a number of very high-impedance 
(bridging) loads to a very low-impedance source.  Tapes are usually 
ploughed-in at a depth of about 8”; however, some installations have it 
laying on the surface.  Systems are designed to deliver about 9 gpm/acre 
- 24/7 in worst-case drought conditions.  Tape emitters are extremely 
susceptible to plugging.  Accordingly, manufacturers provide fairly 
elaborate filtration systems.  The allowable particle size varies 
somewhat with the manufacturer but it is always quite small.  Tape, 
especially buried, is subject to varmints.  This problem has not been 
entirely resolved.

For some row crops and often in orchards, an above-ground round trunk 
drip line is sometimes used.  Many installations have a large buried 
trunk line with risers and valves at intervals to which smaller, local 
lines are connected.  With most all trellised crops (grapes, 
blueberries, hops, etc.), the trunk line is suspended from the trellis a 
few inches above the ground (but sometimes laying on the ground).  With 
a manufacturer-supplied tool, holes are punched at desired intervals and 
small [micro] drip lines are inserted.  These may be either open on the 
end or have emitters attached.

Flow through these open micro-drip lines is determined by pressure and 
length.  The various emitters available have published flow rates.  You 
may want to look carefully at these, however, as they may involve 
internal sharp right-angle turns to regulate flow.  Also, some systems 
offer emitters that are pushed right in to the trunk line.  These 
components are most readily available through Lowe’s or Home Depot - or 
other garden centers.  The rated operating pressure is 10 psi, I think. 
  And there are also many commercial systems available.

Again, consider trunk line diameter and length versus your flow 
requirements.  The manufacturers have published tables to assist you in 

Again, particle size is a consideration in these systems, so be prepared 
to have a strainer with the appropriate screen mesh installed.  In the 
case of compost tea, you may want to have several strainers of 
progressively smaller mesh sizes.  And again, if you use one of these 
systems, don’t use their pressure regulator!

There are several ways to non-destructively regulate pressure:

1. Control pump speed.  This can be done electronically when a DC or a 
3-phase AC pump motor is used.   An expensive approach.

2. Maybe the best method is to have an overflow standpipe.  At 0.433 psi 
per foot of head, this would be a pipe 23’ tall (for 10 psi static 
pressure - much under 1 Atm.) – returning to the tank.  This might be 
the most practical for you.  But whatever pressure is specified for the 
system, it must be constant.  If use this approach, your pump must have 
the capacity to provide at least some overflow continuously - to 
maintain the static trunk line pressure.

3. A much less desirable method is to provide a bypass ball valve after 
the pump to return excess material to the tank.  Not recommended – 
possible velocity and impact issues - and variable flow rates.

ABOVE ALL ELSE – Provide a washout fitting or valve at the end of each 
line!  Sediments and growing things will accumulate in the system.  You 
will have to periodically flush and clean (using bleach and/or Hydrogen 
Peroxide (32% - Beware!)) the system.

I suggest you make a trip to any of the above-mentioned stores and see 
what they have to offer – might give you some ideas.  While there are 
several manufacturers of these systems, the one that comes immediately 
to mind is Rain Bird - but there are other good ones.  For me, there is 
nothing like looking at the stuff in flesh and actually seeing how it 
all goes together…

AND – don’t overlook WATER QUALITY!  With drought in many parts of the 
country resulting in falling aquifers, we’re seeing a dramatic rise in 
serious quality issues - mostly bicarbonates - sometimes Manganese and 
Iron - and sometimes salt.  If your water is from a public utility, ask 
them for a water MINERAL analysis.  If you’re using water from any other 
source, get an irrigation water test.  Depending upon where you are, 
your water chemistry can be changing fast - even from a public utility. 
  Depending upon your soil type and water, bad water can literally turn 
your soil to stone.

What’s in your water becomes part of your soil!™

Finally, we strongly, strongly recommend AGAINST using manure compost 
for teas.  There is much more to compost, itself.

By the way, ACRESUSA published a book several years ago, titled, “Ask 
The Plant”.  It is a very valuable resource.

Frank Schultz

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