"Fact you monitor gives off more radiation than a ton a fertilizer even if you tripled the amounts."


the radiation exposure from your monitor is nothing like the radiation exposure from inhaled radon progeny...computer monitor radiation is external and electromagnetic...tobacco smoke radiation is internal ionizing alpha radiation

you can't compare the two sources of radiation because they're different...light, heat, and sound are types of radiation too...your monitor emits electromagnetic or gamma radiation...alpha and beta radiation are examples of ionizing radiation which is the same type as found in the atom bomb

the ionizing alpha radiation in tobacco smoke is the most active type of radiation (ie: gives off a lot of particles)...alpha radiation doesn't penetrate very far into your body so its a relatively low form of external exposure (the radiation is stopped/absorbed by the epidermus) but when its lodged inside your lungs and bones and organs, its can cause serious damage in small localized areas

exposure to computer monitor radiation stops when you move away from or turn off your computer...the radiation in tobacco smoke gets lodged inside your body where it continues to expose your body to ionizing radiation for DECADES...radon gas breaks down like this:

radon 222 - half life 3.8 days
polonium 218 - half life 3 minutes
lead 214 - half life 27 mins
bismuth 214 - half life 20 minutes
polonium 214 - half life 180 microseconds
at this point in the decay chain, it is a greater threat to tobacco smokers
lead 210 - half life 22 years
polonium 210 - half life 138 days
lead 206 - stable (no radiation)

If smoking is the root cause of cancer then why does chewing tobacco cause cancer?

"Smokeless tobacco users increase their risks of cancers of the oral cavity, pharynx (throat), larynx, and esophagus. Oral cancer can include cancer of the lip, tongue, cheeks, gums, and the floor and roof of the mouth.

People who use snuff for a long time have a much greater risk for cancer of the cheek and gum than people who do not use tobacco.

The possible increased risk for other types of cancer from smokeless tobacco is being studied."

If its the fertilizer like you suggest then any food grown with chemical fertilizers would cause cancer at the same rate as chewing tobacco.

I think you should measure the radiation emitted by the finished pot product. Then you coud detemine the real difference. I have smoked lots of organic weed that didn't burn because it couldn't be flushed properly. I think that flushing is an important step that cleans the weed so that it
s better for smoking. Clean weed and very resinous high potentcy weed, like White Widow is best because there's a lower plant to trichome ratio. Or bubble hash. How much radiation do the trichomes themselves emit? Inorganic fertilizers, in a sense, add to the biomass of the planet. So if we can do so in a responsible fashion, we will be able to support a larger population. The world cannot be fed without fertilizer, organic or other, so I think more research should is certainly necessary.

"If smoking is the root cause of cancer then why does chewing tobacco cause cancer? If its the fertilizer like you suggest then any food grown with chemical fertilizers would cause cancer at the same rate as chewing tobacco."

If intestinal cancer rates were tracked in both organic and non-organic food eaters, you would notice a profound difference.

People who chew and smoke tobacco generally do so more often than they eat - chemy tobacco cancers, in that case, will show up more often than intestinal cancers.

"I think you should measure the radiation emitted by the finished pot product. "

Difficult to measure. It shows up more easily because it gathers in the high-phosphate ferts and in the lungs..... the next test, I would imagine, would be the soil of long-time tobacco land....perhaps it would be there in profound concentration.



"Then you coud detemine the real difference. I have smoked lots of organic weed that didn't burn because it couldn't be flushed properly. I think that flushing is an important step that cleans the weed so that its better for smoking."

Undoubtedly.



"Clean weed and very resinous high potentcy weed, like White Widow is best because there's a lower plant to trichome ratio. Or bubble hash."

Absolutely....these are things that can be done to make cannabis safer....but nothing beats shelling out the bucks (and learning the art) of organics....if you care about lung cancer and all.


"How much radiation do the trichomes themselves emit?"

They don't.....it's the Polonium 210, Lead 210 and Radium metal particles hitching a ride on the trichomes that emit the radiation......we are talking about very tiny particles that regular scientists can only really measure when concentrated in fertilizers, and sometimes in the lungs themselves.





"Inorganic fertilizers, in a sense, add to the biomass of the planet. So if we can do so in a responsible fashion, we will be able to support a larger population."

1) We can't do so in "a responsible fashion" cause all chem ferts kill soil microbes.
2) We don't want to "support a larger population" - we want a universal standard of living that will result in a leveling off-of population (people in poor countries have lots of kids as a form of social safety net - give them a real safety net and they won't have so many kids)




"The world cannot be fed without fertilizer, organic or other, so I think more research should is certainly necessary. "

The chem fert scam is enormous and ongoing. If you would like to learn more, type in "Green Revolution" into www.google.ca or www.dogpile.com.

"If smoking is the root cause of cancer then why does chewing tobacco cause cancer?"

excellent question

chewing tobacco was often thought to be safe because it delivered nicotine without the combustion by-products of smoke that were believed to be the main cause of lung cancer...it seemed like common sense

researchers have suggested that radioactive polonium 210 in chewing tobacco is a likely cause of oral cancers:
http://www.acdaoralhealth.org/conseq.html


"If its the fertilizer like you suggest then any food grown with chemical fertilizers would cause cancer at the same rate as chewing tobacco."

another excellent point

radioactive particles are everywhere; soil contains radium 226 strontium etc....for the purposes of this discussion, i refer only to radiation from decay of radon gas

almost all grain, fruit, vegetables, and meat (including organic food) contains radioactive particles...naturally occuring radioactive radon gas seeps out of the ground in almost all farming areas...radon gas accumulation in homes is responsible for more lung cancer than second hand tobacco smoke...soil samples taken from the wilderness soil and arctic lichen reveals that polonium 210 is an unavoidable part of the food chain (the elk eat the lichen off the rocks and the innuit hunt and eat the elk which has Po210 accumulated in its body fat)...applying chemical fertilizer to soil ADDS radioactive particles which build up over years of repeated use....when researchers go out to take soil samples to test for naturally occuring polonium, they have to find a sample far from agricultural areas to avoid messing up the results from fertilizer radiation buildup.

tobacco has higher levels of polonium than your average food crop...tobacco is a low lying leafy plant that requires intensive farming techniques and superphosphate fertilizer...tobacco is grown in sunny dry conditions in soil that has been depleted by decades of commerical farming techniques....the leaves are broad and sticky with little hairs that trap airborne particles...the tobacco fields are busy places where tractors are frequently applying farm chemicals and tilling....this activity raises a lot of dust which is trapped on the tobacco leaves....insoluble radioactive particles from both fertilizer and naturally occuring sources attach themselves to the outside of the tobacco leaves and are not easily washed off....soluble radioactive particles are drawn up thru the root system and distributed thru the leaves but their concentration decreases as you move up the plant...unfortunately, tobacco is a very low plant

in comparison, most fruit grows higher from the ground and has a smooth skin or inedible peel...there are foods that have higher levels of polonium....there are also farming areas with lower levels of naturally occuring polonium in the soil...it would be a lot safer if farmers didn't repeatedly apply a product with needlessly elevated levels of radiation that persists in the soil and builds up for decades...some studies have been done on the radioactive exposure from a standard western european diet which showed the annual radiation exposure exceeded the maximum safe exposure for nuclear plant employees.

more importantly, chewing tobacco is a highly processed product with a number of toxic ingredients at levels dangerous to health...eating a single cuban cigar might kill you...the chewing tobacco is held in the mouth against sensitive mucus membranes for long periods of time....meanwhile, fresh brocolli is full of heathy life sustaining ingredients which help fight cancers...don't stop eating food: researchers say that the level of radiation in food is pretty safe but the problem is that radiation exposure is additive...eating commercial farm food, chewing tobacco, smoking, x-rays, and even flying in an airplane can quickly add up to unsafe levels of radiation

whew...there is a lot of info here...i can back up every claim here so feel free to question anything and everything

"I think you should measure the radiation emitted by the finished pot product."

thats a good idea...many researchers have measured the polonium in tobacco smoke and some have suggested a direct connection between polonium in tobacco and chemical fertilizer...they suggested that the prime source of polonium contamination is from soil/fertilizer dust and naturally occuring radon gas which easily attach themselves to the broad low lying sticky tobacco leaves

several things make pot safer than tobacco in relation to chemical fertilizer radiation:

- pot leaves are usually not smoked or chewed

- low addictive potential and higher potency flowers means less cannabs must be consumed to reach the desired dose...in contrast, daily tobacco smokers often go through an ounce of plant material a day

- outdoor cannabis does not require extensive tilling or heavy farm equipment which would disturb the soil and raise insoluble radioactive particles attached to soil dust...in addition, cannabis grows higher off the ground than tobacco and is usually not subject to farm dust storms (unless you're growing pot in a corn patch)

- indoor cannabis is exposed to much less soil/fertilizer dust and is often grown hydroponically...hydroponic fertilizers contain soluble salts which wash out of the human body in a few days...the soluble radioactive particles are taken up by the root system and decrease in concentration as they move up the plant...most cannabis flowers are taken from the extremities of the plant....commercial chemical fertilizer contains a much higher ratio of insoluble radioactive particles which persist in soil and the human body for a very long time

i am not suggesting that smoking organic leaves is safe but rather that its the safer, smarter thing to do if you've already made the decision to smoke cannabis and/or tobacco

"whew...there is a lot of info here...i can back up every claim here so feel free to question anything and everything"

Not questioning you but rockwool has been in use in European greenhouses since 1969 as of 1986 50% of all greenhouse vegetables were grown in rockwool. Since rockwool has no nutrients of its own all fertilizers have too be added, making anything grown in them higher in polonium 210 then tobacco products grown in soil with just some of the nutrients being added in the form of fertilizers. If you were right then European people would have a higher cancer rate then most other countries. Funny thing is Europe has a lower rate of digestive and lung cancer then in America.

One other question for you is where do you think organic fertilizers come from. Dave makes the example of fertilizers coming from animal waste, but before there were animals there were plants. Since the first plants could only get there nutrients from minerals dissolved in water this has too be where all fertilizers come from. So whether its mined or absorbed by the plants ultimately all fertilizers come from the same place (mineral deposits). So why would organic fertilizers not contain the same amount of radiation?

Another point is you make is that the radiation comes from particulate matter in the air that gets trapped in the leaves of tobacco plants. What do you think happens when you breath? Your lungs trap all kinks of particulate much better then tobacco leaves.

"Not questioning you but rockwool has been in use in European greenhouses since 1969 as of 1986 50% of all greenhouse vegetables were grown in rockwool. Since rockwool has no nutrients of its own all fertilizers have too be added, making anything grown in them higher in polonium 210 then tobacco products grown in soil with just some of the nutrients being added in the form of fertilizers. If you were right then European people would have a higher cancer rate then most other countries. Funny thing is Europe has a lower rate of digestive and lung cancer then in America."

First - please source your info on cancer rates. Second ... have you considered it possible that Europeans eat less meat and sugar than Americans and have stricter enviro standards?




"One other question for you is where do you think organic fertilizers come from. Dave makes the example of fertilizers coming from animal waste, but before there were animals there were plants. Since the first plants could only get there nutrients from minerals dissolved in water this has too be where all fertilizers come from. So whether its mined or absorbed by the plants ultimately all fertilizers come from the same place (mineral deposits). So why would organic fertilizers not contain the same amount of radiation?

Apatite rock is the source of phosphate in chemical fertilizers....the seashells, kelp and bird guanos that have loads of naturally occuring phosphorus do not contain the polonium, radium and lead contained in the apatite. The chemical companies took a phosphate shortcut - anything for a quick buck.





"Another point is you make is that the radiation comes from particulate matter in the air that gets trapped in the leaves of tobacco plants. What do you think happens when you breath? Your lungs trap all kinks of particulate much better then tobacco leaves. "

Actually, if you hung around a dusty tobacco field all your life, you might find yourself with pritty hot lungs. Most people do not breath in the same amount of radiation that tobacco leaves do, because most folks don't get inundated with chemical fertilizers like tobacco plants are.

Peace
Since we are on the subject, heres some research from sometime ago, on hydro.Introduction
In preparation for writing this paper, I read the related papers from previous HSA proceedings. I am impressed by the amount of useful information. The annual meeting and proceedings of HSA have become an important source of technical information on the hydroponic culture of plants. This information is not necessarily available at the annual meetings of related professional societies such as The American Society for Horticultural Science, or The American Society of Agronomy.

It was necessary for me to read other papers because many of them discuss nutrient management in recirculating hydroponic systems. Authors at every meeting in the past 5 years have stressed the need to recirculate and reuse nutrient solutions to reduce environmental and economic costs. Dr. Pieter Schippers (1991 HSA proceedings) reviewed nutrient management and clearly indicated the need for data when he said, "One of the weakest points in hydroponics...is the lack of information on managing the nutrient solution." I was moderately surprised to find that previous authors recommended measuring the concentrations of individual nutrients in solution as a key to nutrient control and maintenance. Monitoring ions in solution is unnecessary. Even worse, the rapid depletion of some nutrients often causes people to add toxic amounts of nutrients to the solution. Monitoring solutions is interesting, but it is not the key to effective maintenance.

Managing nutrients by mass balance

During the past 12 years, we have managed nutrients in closed hydroponic systems according to the principle of "mass balance," which means that the mass of nutrients is either in solution or in the plants. We add nutrients to the solution depending on what we want the plant to take up.

Plants quickly remove their daily supply of some nutrients while other nutrients accumulate. This means that the concentrations of nitrogen, phosphorous, and potassium can be at low levels in the solution (0.1 mM or a few ppm) because these nutrients are in the plant, where we want them. Maintaining a high concentrations of nutrients in the solution can result in excessive uptake that can lead to nutrient imbalances.

For example, the water removed from solution through transpiration must be replaced and it is necessary to have about 0.5 mM phosphorous in the refill solution. If the refill solution was added once each day, the phosphorous would be absorbed by the plant in a few hours and the solution phosphorous concentration would be close to zero. This does not indicate a deficiency, rather it indicates a healthy plant with rapid nutrient uptake. If the phosphorous level is maintained at 0.5 mM in the recirculating solution, the phosphorous concentration in the plant can increase to 1% of the dry mass, which is 3 times higher than the optimum in most plants. This high phosphorous level can induce iron and zinc deficiency (Chaney and Coulombe, 1982).


Although organic pH buffers can be used to stabilize pH (Bugbee and Salisbury, 1985), in the long run it is better and less expensive to use an automated pH control system that adds acid or base to the solution. These systems require 3 components: a pH electrode, a pH controller, and a solenoid. We have had 7 pH control systems in continuous operation at the Utah State University Crop Physiology Laboratory during the past 8 years. It is useful to pass on our experience with the system components

Last year, we discovered that Mn deficiency predisposed the plants to phythium infection. A student worker accidently used MgCl2 in place of MnCl2 for a micronutrient stock solution and we didn't discover the mistake for several months because we were doing short (25 day) studies and there was enough Mn contamination so that no visual symptoms were apparent (growth rate was reduced only about 15% and there was about 10 mg kg-1 Mn in the leaf tissue). During this time several of the systems became infected with phythium. The same systems have never been infected when Mn was adequate. Copper is well known to suppress microbial growth, but increased copper levels are toxic to plants. Manganese and zinc (divalent cations) may have a similar disease suppressive potential, but are less toxic to plants. In the interest of minimizing phythium growth, we have increased solution Mn to a level higher than that required for optimum growth. Careful studies will be required to confirm the beneficial effects of Mn on disease suppression; meanwhile, there is little disadvantage to maintaining manganese, zinc, and copper levels slightly above the minimum required for plant growth

pH monitoring and control

Is pH control important?

Most people assume pH control is essential, but there is considerable misunderstanding about the effect of pH on plant growth. Plants grow equally well between pH 4 and 7, if nutrients do not become limiting. This is because the direct effects of pH on root growth are small, the problem is reduced nutrient availability at high and low pH. The recommended pH for hydroponic culture is between 5.5 to 5.8 because overall availability of nutrients is optimized at a slightly acid pH. The availabilities of Mn, Cu, Zn and especially Fe are reduced at higher pH, and there is a small decrease in availability of P, K, Ca, Mg at lower pH. Reduced availability means reduced nutrient uptake, but not necessarily nutrient deficiency.

Unfortunately, hydroponic systems are so poorly buffered that it is difficult to keep the pH between 4 and 7 without automatic pH control. Phosphorous (H2PO4 to HPO4) in solution buffers pH, but if phosphorous is maintained at levels that are adequate to stabilize pH (1 to 10 mM), it becomes toxic to plants. Plants actively absorb phosphorous from solution so a circulating solution, with about 0.05 mM P has much less buffering capacity than the fresh refill solution that is added to replace transpiration losses. Figure 2a is a titration curve of fresh refill solution compared to the recirculating solution. Six mmoles of base were required to raise the pH of fresh solution from 5.8 to 8, but only 1 mmole of base raised the pH of the circulating solution to 8. Figure 2b shows the slopes (derivatives) of the lines in Figure 2a. Figure 2b clearly shows poor buffering of the circulating solution between pH 5 to 9; small amounts of acid or base rapidly change the solution pH. The fresh refill solution is buffered by phosphorous, which has its maximum buffering capacity at pH 7.2. This point is called the pKa of the buffer and it is the point at which half of the phosphorous is in the H2PO4 form and half is in the HPO4 form. In other words, the phosphate ion absorbs and desorbs hydrogen ions to stabilize the pH. Unfortunately, phosphorous is quickly removed from the solution.

We were surprised to find that the circulating solution was better buffered below pH 5 than the fresh solution. The reasons for this are unclear, we cannot identify compounds in the refill solution that provide buffering capacity at pH 4. We are preparing to repeat these measurements and are investigating this finding.

How important is maintaining pH 5.8?

We control the pH at 4 to study root respiration (to eliminate bicarbonate in solution). We compared growth at pH 4 and pH 5.8 with wheat and were not able to find a significant difference in root growth rate or root metabolism. We now routinely grow wheat crops at pH 4 during the entire life cycle. However, although there is usually a broad optimum pH, it is still best to maintain pH at about 5.8 to optimize nutrient availability. pH levels below 4 may start to reduce root growth, in one study our pH control solenoid failed just after seed germination and the pH went to 2.5 for 48 hours. The roots turned brown and died, but new roots quickly grew back and the plants appeared to make a complete recovery.

An automated pH Control System.

Although organic pH buffers can be used to stabilize pH (Bugbee and Salisbury, 1985), in the long run it is better and less expensive to use an automated pH control system that adds acid or base to the solution. These systems require 3 components: a pH electrode, a pH controller, and a solenoid. We have had 7 pH control systems in continuous operation at the Utah State University Crop Physiology Laboratory during the past 8 years. It is useful to pass on our experience with the system components.

pH electrodes. We have not found that expensive electrodes last any longer than cheap electrodes (about 2 years per electrode) so we use cheap electrodes. We currently use a general purpose pH electrode from Omega (model PHE-4201; $49). It appears to be important to avoid rapid flow of solution across the tip of the electrode. Rapid response time is not important and the high flow appears to greatly decrease electrode life and also causes significant calibration drift. We check the calibration of the electrode every 2 to 3 months and adjust it if necessary.

pH controller. In about 1987 a new, digital-display pH controller became available (model 3671, $225., Whatman Lab Sales, Hillsboro, OR, 1-800-942-8626). This controller has been excellent in our laboratory - we have yet to have a controller fail. Automatic temperature control is completely available with the controller for another $65. but it is unnecessary.

When the pH increases to 5.8, the controller opens a solenoid that allows nitric acid (HNO3) to flow into the bulk solution. When nitrate nitrogen is used the solution pH increases as the nitrate is absorbed so only one solenoid is necessary. The acid inlet should be in close proximity to the tip of the pH electrode so that frequent small additions of acid occur and the bulk solution pH is stable.

Acid/base solenoid. A peristaltic pump can be used to add acid or base, but a solenoid is less expensive. Proper solenoid selection is important because common solenoids quickly deteriorate from acid corrosion. We use a shielded core acid solenoid from The Automatic Switch Company (ASCO, model D8260G56V or G53V; about $76.). These solenoids do not corrode, but in our experience, about 50% of the diaphragms in the valves failed in less than 2 years in continuous use. The valves are rated for a million cycles so they should last at least 10 years. We are currently working with ASCO to determine the cause of the premature failure. We previously used ASCO valve number D8260G54V, but this valve is not shielded core and corrodes in less than a year, even with 0.1 molar acid. Most plumbing suppliers sell ASCO solenoids, it pays to shop around for good price and quick delivery. Many other companies sell acid resistant valves that may be suitable, but some require a transformer for 24 volt operation.

The total cost (1995) of a pH control system as described above is $350. to $400. depending on availability of system components.


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Why add silicon to nutrient solution?

Although silicon has not been recognized as an essential element for higher plants, its beneficial effects have been shown in many plants. Silicon is abundant in all field grown plants, but it is not present in most hydroponic solutions. Silicon has long been recognized as particularly important to rice growth, but a recent study indicated that it may only be important during pollination in rice (Ma et al. 1989). The beneficial effects of silicon (Si) are twofold: 1) it protects against insect and disease attack (Cherif et al. 1994; Winslow, 1992; Samuels, 1991), and 2) it protects against toxicity of metals (Vlamis and Williams, 1967; Baylis et al. 1994). For these reasons, I recommend adding silicon (about 0.1 mM) to nutrient solutions for all plants unless the added cost outweighs its advantages.


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Experiences with phythium control in hydroponic solution

The phythium fungus has been the only serious disease we have encountered in our systems, and disease problems have been relatively rare, particularly when all parts of the system are kept covered to keep dust and dirt particles away from the solution. Every plant pathologist on the planet recommends sanitation as the best control procedure for phythium, yet many hydroponic systems are not as well sealed as they should be.

Last year, we discovered that Mn deficiency predisposed the plants to phythium infection. A student worker accidently used MgCl2 in place of MnCl2 for a micronutrient stock solution and we didn't discover the mistake for several months because we were doing short (25 day) studies and there was enough Mn contamination so that no visual symptoms were apparent (growth rate was reduced only about 15% and there was about 10 mg kg-1 Mn in the leaf tissue). During this time several of the systems became infected with phythium. The same systems have never been infected when Mn was adequate. Copper is well known to suppress microbial growth, but increased copper levels are toxic to plants. Manganese and zinc (divalent cations) may have a similar disease suppressive potential, but are less toxic to plants. In the interest of minimizing phythium growth, we have increased solution Mn to a level higher than that required for optimum growth. Careful studies will be required to confirm the beneficial effects of Mn on disease suppression; meanwhile, there is little disadvantage to maintaining manganese, zinc, and copper levels slightly above the minimum required for plant growth.


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Designing hydroponic systems: The importance of flow rate

Most hydroponic systems have inadequate flow rates, which results in reduced oxygen levels at root surfaces. This stresses roots and can increase the incidence of disease. Oxygen is soluble only as a micronutrient, yet its uptake rate is much faster than any other nutrient element.

The nutrient film technique was designed to improve aeration of the nutrient solution because of the thin film of solution, but the slow flow rates in NFT cause channeling of the solution and reduced flow to areas with dense roots. The root surfaces in these areas become anaerobic, which diminishes root respiration, reduces nutrient uptake, increases N losses via denitrification, and makes roots susceptible to infection. The problems with the nutrient film technique have been discussed by several authors. Bugbee and Salisbury (1989) discuss the importance of flow rate and adequate root-zone oxygen levels.


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Isolite: A new substrate for hydroponics

Many different substrates are used for plant support in hydroponic culture, but one of the unique requirements for research is that the media be easily separated from the roots. Peat, perlite, and vermiculite are good substrates but roots and root hairs grow into these substrates, so they are unsuitable for studies of root size and morphology. Sand can easily be removed from roots, but roots grown in sand are shorter and thicker than hydroponic roots because the sand particles are so dense. We have also found that plant growth in sand is less than in other substrates, presumably because of reduced root growth. Calcined clay (brand names: Turface, Profile, Arcillite) was the medium of choice for research hydroponics for many years because it can easily be removed from roots. Calcined clay, however, has two disadvantages: 1) It is not chemically inert. Different batches supply different amounts of available nutrients and this causes variable results. It can be repeatedly rinsed in nutrient solution to desorb undesirable nutrients, but this adds to its cost. 2) Calcined clay is not a uniform particle size, and the water holding capacity depends on particle size. Not all batches are the same.

We recently tested and began using an extruded, diatomaceous-earth product called Isolite. Isolite is mined off the coast of Japan where there is a unique diatomaceous-earth deposit mixed with 5% clay. The clay acts as a binder in the extrusion and baking of the diatomaceous-earth. Diatomaceous-earth materials were originally organisms composed primarily of silicon dioxide (SiO2). Silicon dioxide is physically and chemically inert and these characteristics make it useful for horticultural applications like putting greens and urban trees where the soil is subject to severe compaction. Isolite is available in particle sizes from 1 to 10-mm diameter. Our tests indicate that Isolite is chemically inert and has good water holding characteristics. Its disadvantage is cost at $1.22 per Liter ($.79 per pound) for small quantities, although it can be reused. We have reused it after rinsing and drying at 80 C. Isolite is made by Sumitomo Corp. and is available in the USA from Sundine Enterprises, Arvada, CO; 303-423-8669.


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Microorganisms and organic compounds in the solution: Is filtering useful?

Many people think that filtering the recirculating solution is useful, but we have never filtered our solutions. Our measurements indicate that total organic carbon in the recirculating solution does not exceed 15 mg per liter, even near the end of a 2 month life cycle. About 30% of the organic carbon in the solution is in the chelating agent. Total organic carbon includes the carbon that is in microbial biomass, so it is clear that neither organic compounds nor microorganisms are at high levels in the solution. The solution also appears as clear prior to harvest at 80 days as fresh solution.

Roots leak organic compounds, but there is an equilibrium between microorganisms on root surfaces and the exudates so that compounds are degraded to CO2 at the root surface. Estimates of the quantity of root exudates vary widely, but there is considerable evidence that carbon efflux increases when plants are stressed (Barber and Gunn, 1974; Smucker, 1984; Haller and Stolp, 1985). Bowen and Rovira (1976) found that roots in solution culture produce smaller quantities of exudate than in soil. Trollenier and Hect-Buchholz (1984) found that reduced root growth due to inadequate aeration in hydroponic culture was accompanied by a dramatic increase in root microbe population, which they attributed to increased exudation from roots. The bottom line is that healthy roots in a well aerated hydroponic system should not increase the microorganisms or organics in the solution and filtering is thus unnecessary.


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Summary comments on specific elements

Nitrogen: Plant requirements for nitrogen are sometimes larger than all of the other elements combined. It can thus be difficult to supply nitrogen in the refill solution without adding excess amounts of other cations. The best solution is to use nitric acid (HNO3) for pH control. This can supply 50% of the nitrogen needs of the crop without adding excess cations. If extra nitrogen is required, ammonium nitrate can be added to the pH control solution. However, because ammonium decreases the uptake of other cations (K, Ca, Mg, and micronutrients) I do not recommend its use in hydroponic solutions unless extra nitrogen is required by the crop for maximum yields.

Phosphorous and Potassium are rapidly drawn down to µM levels is solution. These low levels do not mean that the plant is starving for these elements, it means that the plant is healthy and actively absorbed these elements from solution.

Calcium requirements are almost 3 times higher for dicots than for monocots (grasses). Calcium is nontoxic, even at high tissue concentrations, but it accumulates in solution if too much is added to the refill solution.

Magnesium is highly mobile and can accumulate to toxic levels in upper leaves if the solution concentration is too high.


Now is that a read