Are we overfertilizing our plants?

[63pmp]

This is all a bit long winded and has taken some time, but I hope it makes sense. It only covers a very small section on the art of fertilising.

This is the basics

All plants need 16 elements for survival. Of the 16, 3 (carbon, hydrogen and oxygen) come from the air and water in the growing medium. All the rest come from the growing medium and enter plants through the roots. If any one of these elements is deficient, or absent, then the plant will not grow, instead it will weaken and perhaps die. The elements have to be within certain ratios to each other for optimum growth. Trace elements are toxic in excessively high concentrations.
The aim of fertilizing is to provide all the elements required, in appropriate ratios, for optimum plant health. Nutrient s become limiting when plant demand exceeds availability. Maximum growth rate is set by plant genetics, so once you supply everything a plant needs, it will only grow as fast as it can.
The problem with plant nutrients is that they are mostly salts. Each species of plant will have its own tolerance to salt toxicity. This limits the amount of fertilizer that can be applied. Excess salinity from fertilizer causes what is known as fertilizer burn. This is what happens when you over fertilize.
Not all fertilizers are balanced or complete, each will have some nutrient missing and another in abundance. Thus it becomes important to know what the chemical composition of your fertilizer is, and what extra elements need to be added, in relation to the main fertilizer, to bring it into balance/completeness. If you don’t balance but simply put more on to get the growth you want you run the risk of salinity problems. As well as wasting a lot of nutrient. You will get better growth using a quarter of the nutrients but balanced, than putting on lots with one element deficient. This is the main issue with fertilizing, if you don’t know what you have or what is missing, then you are really only stumbling around in the dark with hit and miss fert schemes, wasting money.

What I now do

Previously, to this year I have always fertilized with organic fish emulsion type fertilizers, but these have become too expensive. Charlie Carp is $18/ liter in my local shops, this will last one or two fertilizing days. Thrive is $12 / 500g, this will last for about two years at current application rates. Because of this cost I have gone completely inorganic and plants are growing better then ever.

Some sciency type stuff

I use well water which has an electrical conductivity of 370 uS/cm (approx 170 ppm salts). The published limit for fertilizer solutions for salt sensitive plants is 1500 uS/cm Handrek and Black. (Kelley’s solubridge figures converted from old units to new; gives 500 – 1250 uS/cm (I like these numbers)). Unfortunately there is no published data for what is safe for Japanese maple or trident maple, which has forced me to experiment. Japanese maple would be my most sensitive plant. I find rock hornbeams easier to care for than Japanese Maples, where I live. I don’t fertilize when it’s raining, and always water before application of fertilizer. I apply the fertilizer solution so that excess runs out of the bottom of the pots. I fertilize every tree once a week, though you could fertilize everyday with these solutions if you wanted.
This spring I have been fertilizing with Aquasol. Through trial and error I have found 1 level teaspoon of Aqausol per 9Litres of water is workable with Trident maples.
This gives a final concentration of 102 ppm N, 17.8 ppm P, & 80 ppm K. With an EC of 715 uS/cm (with my well water). This corresponds somewhat with Kelley’s 100ppm recommendation and salinity values.
For Japanese maples I have found that a teaspoon is too strong for them and so use ¼ a level teaspoon of Aqausol. This gives an EC of 460 uS/cm. And 25ppm N. Somewhat lower than the published N numbers but close to Kelley’s bottom EC suggestion.
My biggest problem is the saline well water which uses up a lot of fertilizer space, 370 uS or approx 170 ppm of salts.

Finally, Aqausol has no magnesium or Calcium in it because these metals form an insoluble compound with phosphorous. But at such low concentrations being used they can be mixed together into the one solution and watered, a precipitate will settle out of solution eventually, but the trees have been fertilized before that happens 1 teaspoon of Epsom salts (magnesium sulphate) provides about 40 ppm Mg in 9L of water.

Paul

[Bretts]

Paul correct me if I am wrong but it sounds like you are testing the amount of salt in your liqued fertiliser dilute. The paragraph you quoted suggests testing the soil.
Have you done any soil test to see what is happening with the salt content of the soil with your fertilising regime?
Like the paragraph states

The best method of preventing overfertilization is to use a
sound fertilization program combined with periodic soil testing for
nitrogen and potassium as well as testing for soluble salts by usmg a
solu-bridge.

I would like to do this but the device is very expensive. Then as you say it will take some time to come up with relative data for each species.

[63pmp]

Bretts,

I bought my EC meter from Activon scientific years ago. They used to have have good affordable meters, this is similar to the model I have.

http://www.eutechinst.com/pdt-para-cond ... con11.html

You could also try Selby Biolab, they supply lab equipment.

The cheapest option is Techtrader, they sell good second hand lab equipment. Check here

http://www.techtrader.com.au/shop/categ ... nductivity

Of course local labs will test an EC fairly cheaply and you don't have do it too often.

I only test the solution going in, I've not really wanted to dig holes in my growing pots. It would be interesting to see what salts hang around after a couple of days watering leaching the mix.

I'm waiting on a water test for my new well water so I'll wait and see what it says, If its high in chloride and sodium I might do a test. But i think most stuff gets leached out fairly quickly. You need a fair amount of extract to get the probe into it cleanly, maybe 100ml of water, that requires the same volume of potting mix.

Paul

[Bretts]

Paul the quoted paragraph states.

Soil nitrates should be maintained at not over 100 parts
per million and soil potassium levels should not be greater than 300
parts per million on a soil basis.

Maybe I am missing something here but it seems you are comparing the Liquid fertiliser dilute to Kelly's soil PPM

This gives a final concentration of 102 ppm N, 17.8 ppm P, & 80 ppm K. With an EC of 715 uS/cm (with my well water). This corresponds somewhat with Kelley’s 100ppm recommendation and salinity values.

I am very interested in this as I think it must be too much salts that are contributing to my Hornbeam/ J Maple leaf burn. I am now at the stage where I get fresh healthy growth as the old leaves get fringe burn.

I will have to look into a local soil tester. Maybe with all the farming going on around me there is a local testing I can utilise.
Thanks for the info and links.

[63pmp]

Brett,

Been thinking a bit more,

My potting mix is basically quartz river sand, 2-5mm sieved, with about 30% sieved composted pine bark extracted from various potting mixes available at the time. I don't feel that this would hold onto too much salts. I could be wrong of course, as the pine bark would have some cation exchange properties. I think about this some more, its not hard to do the tests, it just means digging holes in my pot and disturbing some Japanese Maple roots (I'm a little scared of this bit).

I do not add any slow release fertilizer to the mix or any other organic material, though being on Ausbonsai has taught me that others do. I know that things like osmocote prills can dump there contents in a hurry during warm weather and cause salinity problems. Also the biological release of nutrients from organic fertilizers increases with warmth, if you are adding extra fertilizer by liquid feeding you could cause salinity problems. Also what is the salinity of the water you are using? In this case I would think a soil EC test would be beneficial.

Paul

[Bretts]

Yep it will be very intresting to get some soil tests done. I tested the house water at the pool place and I remember I was very happy with the result at the time. But I will get a proper test done.
I mentioned in the other thread that Walter suggest that with a free draining mix that requires watering often Hornbeams should be watered with rain water to aviod salt buildup. I figure this means that even if my tap water tests ok it will still be too high for hornbeams.
Since I always figured Walter to live in a cooler climate than me I think there is a good chance this is the problem.

Must be time for a water tank

[Jamie]

i only use tank water for my trees, i did some Ph tests on the mains (although i dont know if this relates to salts) to the collected rain water tank, the mains were very high in alkalinity, where as the rain water had a very neutral level. i figured this would be best for the trees, plus i figured there would be some deposits sitting in the tank at the bottom which could be helpful to the trees in some way or another, (i presume it would have some nutrients in it). it would be interesting to test the soils of my new mix as i have gone from organics to a bit of a mix, (organic and inert) of diatomite, zeolite and a potting soil, generally just from the nurseries own wix which is quite good or whatever i have available at the time.

jamie

[63pmp]

Brett,
I'm finding that different cultivars, vary greatly in their behaviour. I not sure exactly what Waltar grows, I think mostly European hornbeam, which I don’t have, so I can’t speak for them. I have three types, Rock, American and Heart Leaved (C. cordata). Of the three, I only get symptoms from the cordata. Hot weather speeds up the development of the problem due to increased transpiration rates. Here's some photo’s

Hornbeam 1.JPG

The first is how the leaves usually look at the end of summer, not at the beginning.

Hornbeam 2.JPG

This is leaf after over fertilizing showing distortion of the leaf and severe burning of the edges. This process continues to the leaf shrivels up and falls off.
Over fertilizing can cause this, as well as sodium toxicity due to a deficiency of calcium and magnesium. Chloride toxicity can also do similar damage.

These are the symptoms I get with salinity on Japanese maple leaves. It’s taken three to four weeks of non fertilizing for the trees to recover. Older leaves on the right, new growth on left. I should mention that I get more fungal problems on the leaves during wet weather after salinity type damage.

JM 1.JPG

Regarding measurements of EC’s. Unfortunately I’ve made another mistake, that’s two in the one thread. Water extracts for measurements of soil salinity always measure lower than actual soil solution surrounding plant roots itself. This is slight problem, but as long as everyone in the world uses the same procedure when doing salinity tests, the results will correlate with observed plant requirements. But measuring EC of feed solutions and comparing it to soil extract is bad practice.
Unfortunately I get very little time to write these things and rely on a poor memory for more than I should. Thanks for picking up on that. I don’t particularly want to spread untruths.

The next logical step from here would be to conduct a little experiment looking at the effects of various strengths on salinity to maples, hornbeams, whatever. Though this can get expensive if you don’t have access to a lab. Most research scientists do the lab work themselves so they don’t have to pay. I suppose looking at growth and leaf comparisons might be good enough for most people.

Jamie, regarding pH.

pH only measures the concentration of H+ ions in solution, it doesn’t give an indication of salinity. pH is important as it effects the availability of certain nutrients to plants, either too high or too low is problem. pH can be corrected by additions of chemicals, which further lifts the EC. If you have another, better source, than use that. Correcting pH problems is a pain.

Paul

[bonscythe]

Quick one, does the addition of gypsum raise the EC?
Cheers

[63pmp]

Gypsum is a salt of calcium and sulphate. Like any salt dissolved in water, it will raise the EC. However, the benefits of gypsum far outweigh its EC concerns.

For instance. Calcium is easily leached from a potting mix, it washes out with nitrate. So unless there is a source of calcium in the mix, or added with feeding, then the soil quickly becomes calcium deficient. This has problems in that calcium is important for Boron adsorption, calcium also helps to prevent the roots from taking up too much sodium. Another thing is that nitrates will wash out of soil before chloride does, the addition of sulphate helps in getting rid of chloride, which can become toxic after a while if not removed. (doesn't do anything in preventing nitrate leaching) Top dressing a pot with gypsum is a good long term method of getting calcium back into the potting media, if deficient

The ratio between sodium, calcium and magnesium is very important for plant health.

Paul

[bonscythe]

Thanks Paul, some interesting info there.
I'm interested in chucking a little gypsum in my bulk soil mix for potting to stabilise the pH and hopefully negate some of the problems associated with fluctuating pH levels. Just don't really know a % which is both useful but not inhibiting
Cheers

[barefoot]

If you overfertilize it will just leach out as there is very little to hold the nutrients in the soil mixes we use. Overfertilizing is just throwing good money out the door.
Under fertilizing can be due to people using organic fertilizers that don't contain the required levels of nutrients required by the plant or no fertilizer at all. The batches of organic fertilizers vary in levels of NPK. One batch could be great and the next batch of the same product could be well under, requiring double the use.
The big issue is to watch the Bureit in the product. Bureit is the residue of Urea production and has been know to kill citrus trees. Even supposely Organic fertilzers are balancing their NPK with Chemicals especially Urea.
Read the Contents of each fertilizer, vary the brand used each rotation and just what your trees, they will tell you.
Fertilizer regimes are going to change with 'soil' mixtures used and climatic conditions in each person's micro climate. Ask local people what they are doing(maybe just gardner's if no Bonsai people nearby).

[63pmp]

Bonscythe

What do you mean by fluctuating pH? Adding Calcium ions tends to knock the pH down a little as it dislodges Hydrogen ions (acid ions) from exchange sites on colloids humus etc.

But it doesn't have a lasting effect. Factors affecting pH in mix is complicated. Need more of an explanation of what is happening with your mix, and what your ingredients are.



Barefoot,

It depends on what type of growth you want, but assuming you want maximum growth, then nutrients have to be in oversupply all the time for the plant to take what it wants. The trick is to not have too much of an oversupply. Nurseries often collect runoff and treat (sterilize, amend nutrient, salinity, levels) and reuse the solution to save on fertilizing costs. Nutrients leach out fairly quickly so frequent applications of feed are necessary to maintain supply. Over fertilizing is when you push the solution salinity to dangerous levels, up until then the plant is healthy and happy.

Urea is considered an organic fertilizer, even though it's made in a factory, its the same stuff that we excrete in urine. Yes, Biuret is a concern.

Fertilizer regimes do have to change with soil mix, climate, plant etc. Most people go with "is the tree happy or not", and then scratch there heads in confusion when their trees aren't happy.

Paul

[Bretts]

Looking into Gypsum after Jamie brought it up in the other thread It seems it can be a great help in this regard.
As you say Paul it is a great source of Calcium which the guys out at Nutritech call the trucker of all nutrients.
Gypsum also seems to be able to de-salinate the soil

I was planning on starting a thread on leaf burn of the hornbeams so I might save further discussion on your observations if I may for that.
http://www.phoenixtropicals.com/soil.html

Soil Salinity, Deep Soaking and Gypsum
The phrase "salty soil" is a term used to describe soil that has a level of salts dissolved in it that is detrimental to plant growth. There are many different chemical compounds that are classified as salts. Generally speaking, salts are molecules that disassociate when they come into contact with water. By mixing into the water, the salt reduces the ratio of actual water molecules that are present within the liquid.

Water salinity is important to plants because it affects the ability of a plant's roots to take up water. Plants normally regulate how much water they have in their system by actively drinking through their roots. When the water surrounding a plant's roots becomes too salty the salty water does not actually have a lot of water molecules within it, relative to the fresher water within the plant.

Water, like all liquids seeks to evenly distribute itself. The scientific term for this is osmosis. This means that in the case of salty soil the lower concentration of water molecules outside of the roots draws water from the roots with such force that the plant is less able to take in water. The plant then starts to show signs of drought stress. Plant growth is first slowed, because the plant is using a large part of its energy trying to take in water. If these conditions continue the plant will begin to conserve water by allowing its extremities to dry out, which will be first evident on its leaf tips, referred to as salt burn, followed by major branches, and so on.

Salt burn is one of the number one problems the exotic plant gardener will have in Phoenix, and can often kill salt sensitive plants. Keep in mind that fertilizers make the soil more salty, so it is often best to not use them at all on salt sensitive plants.

The best way to minimize salt buildup around a plant is to periodically deep soak/leach the soil. Leaching is done by placing a hose in the basin and letting it flood slowly for many hours. This procedure can be done preventatively for salt sensitive plants 2 to 4 times a year. Sometimes, leaching with water alone, is all that is needed. If this is not effective enough one can try leaching in combination with gypsum.

A fascinating fact is that gypsum is also a salt. So, how is it that adding gypsum can help to reduce the saltiness of a soil? The short answer to this question is that gypsum helps to wash away salts in sodic soil.

A soil is sodic when it has an excessive number of sodium ions in it. In Arizona, the water is high in sodium causing our soils to be sodic. Sodium ions cause a problem for plants because they bond themselves to clay particles and make the soil less permeable, meaning that water and almost every other substance has trouble passing through it. Washing away salts in sodic soils is therefore difficult.

When gypsum dissolves in water, calcium ions are released which displace sodium ions from their bonding sites in the soil. Unlike the sodium ions, the calcium ions open up the soil. A thorough soaking can now wash away excess salts, including any gypsum ions that did not find a bonding site. Interestingly, gypsum is not a harmful salt when thoroughly leached because it permits itself to be quickly washed away. Keep in mind, that using too much gypsum will necessitate more leaching to wash it way so moderate amounts should used.

Formulations of garden gypsum also contain sulfur, which helps to acidify the soil. To leach with gypsum, sprinkle a thin layer of it in the watering basin around the plant. This layer should be just deep enough to hide the ground, similar to a light dusting of snow. The next step is to thoroughly soak in the gypsum by flooding the area around the plant for many hours.

[Bretts]

Our local water has average 60mg/L or 60ppm I believe. Ranging from 40mg/L to 90mg/L. That seems pretty low. It is very hard to find a general salt content for rain water but I did find one that states 6.4mg/L rain water that may increase to 32mg/L by the time it makes it off the roof and into the rain water tank ?

So we could say 3-5 times less salt in Rain water to our local water. But it is still alot less than your water. Next I should be able to get a calculation of that with Fert added just from the fert figures.