NPK

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David Bracey

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NPK
« on: December 05, 2012, 05:13:38 PM »
Here`s another article taken from the  MGS  South Autralian branch`s Newsletter which will be of interest....I hope.

The ABC of NPK

There are three major elements that have a huge impact on various aspects of plant growth. These are Nitrogen (N), Phosphorous (P) and Potassium (K), not only is each element vital but their abundance relative to each other has profound effects.
When reading the label on fertilizer packaging the N, P and K are always written in that order and the numbers expressed are percentages of that element in the product by weight. This is a legal requirement for all fertilizers. Soil scientists tell us that the ratio of these major elements that suit the widest possible range of plants is somewhere around 10 - 1.5 - 8. These are referred to as balanced fertilizers. The word ―complete‖ is reference to the product containing all three N, P and K.

Some fertilizers have quite low percentages of these elements but also incorporate concentrated animal manures - especially from the chicken industry. These give valuable sources of organic carbon and are a major stimulant for soil microbes. They are often much more expensive when viewed only from an element point of view.

Other fertilizers are element only i.e. N, P and K and occasionally with trace elements. Consumers need to realize that they are buying elements, only at a much cheaper price and that they will also need to add good levels of organic material to build up a living healthy soil. Unfortunately cheaper elemental fertilizers are often based around sulphates that can cause leaf burn and wreak havoc on earth worms and microbes. Blended, technical grade elemental fertilizers that are sulphate free, are far superior as they do not cause microbial problems or leaf burn - but you may have to
hunt around to find them

In most cases the added expense of supplying trace elements continuously is not necessary for the home gardener as whole crops of seed or fodder is not being removed. If your plants are veiny or mottled then broad spectrum trace elements are available in 500 g packets. In South Australia trace element deficiencies are often actually an unavailability problem due to high pH.

Nitrogen (N) is the element of growth and stem elongation. High N levels will cause increased leaf size and taller softer plants that are less resistant to heat, drought, wind and frost and the ability to flower and carry fruit can be reduced. Despite these drawbacks very low levels of N will cause plants to be hard and stunted and not able to utilize other elements. N is very rapidly up taken from the soil by soil microbes and plants and excessive watering can physically remove it or allow it to be released to the atmosphere so its addition and incorporation into the soil is
important.

Phosphorus (P) is the element most concerned with root development. It has desirable effects on development of bulbous plants by producing larger stronger bulbs. This also includes plants such as carrots, turnips, parsnips, ornamental bulbs, onions etc. For these plants the proportion of P is elevated For these plants the fertilizer is unbalanced in favour of P. It should be remembered that due to many Australian soils being
very low in P, certain plant families especially Proteaceae and certain heath land plants have become super efficient at extracting P from soil. A ―normal‖ concentration of P, is toxic to them. This has led to the belief that Australian plants in general are P sensitive and this is not the case.

Potassium (K) This is the element that is fundamental in flower and bud formation, flowering and fruiting. For people who grow Mediterranean style plants in hot dry gardens, it is the element that promotes the development of thicker stronger cell walls making plants more heat and frost tolerant. When soils have a greater abundance of K than N, the plants will have better resistance to forming soft sappy runaway growth that will go crisp in the first heatwave. K is also very important in regulating the guard cells either side of the leaf stomata so that moisture loss and leaf temperature are controlled properly depending on soil moisture availability.

In general, assuming there are adequate elements to allow plant growth to occur it is very important to get their relative concentration roughly right. While ―the Balance‖ may be 10 - 1.5 - 8 to suit the widest possible range of plants, the ornamental Mediterranean ratio may be more like 10 - 3 - 12 to have more steady growth from lower N, bigger root development from higher P and harder, stockier more flowery fruity plants from high K. The concentration of elements in the fertilizer bag is of no consequence i.e. 5- 1.5 - 6 and 10 - 3 - 12 and 20 - 6 - 24 are all the same proportions. Just make sure only as much element as the soil requires is used.

The use of animal manures is very good for creating living, carbon rich soils but the elemental starting point for manures is somewhere around 5 - 3 - 1 which is uncomfortably high in N. This is usually overcome by the addition of potash to bring the N- K ratio back to something a bit more realistic. The addition of potash to high N situations is often done with Potassium Sulphate. The word potash has come from alkaline compounds potassium carbonate or potassium hydroxide which is not used now. Do not confuse potash with white powder wood ash which is extremely alkaline and destructive of good soils.

Charcoal is benign or sometimes beneficial.

The manure unbalance is not as bad as it appears as ammonia (NH₄) is usually given off as a gas and thereby looses much of the N. The mulching of gardens with mushroom compost, pea straw, bush litter, etc is essentially adding organic carbon to the soil which will create healthy living soils but they do not add the big three N,P and K.
As soil microbes break down those carbon products, they compete more strongly than plants for any N, P and K and in the short term the plants may be very hard and starved. This is commonly called nitrogen draw down. In this event, use soluble fertilizer to keep plants and microbes satisfied. As far as the economy of building up and maintaining healthy soils is concerned, I have always found it much better to buy animal manures, mulches and elements separately rather than in combination. Animal
manures and chicken litter can usually be bought in the hills, from roadsides for $ 5-00 or even less for a large bag. These will be approximately 5 - 3 - 1 of element. Mulches, which are usually carbon in the form of cellulose, can be bought for a few dollars a bale for pea straw, and contain more or less no NPK as this has long since been transferred into the seeds those plants were growing. Chipped up trees and shrubs are delivered by the cubic metre and because they were living plants, it will contain very small amounts of
nutrient.
When buying elements, not only are the proportions of each element important, but take note of all the total concentration of usable element in the container. As the NPK numbers are in percentages of weight in the product, then a 8 - 3 - 2 blend will be 13% of usable element where as a 20 - 5 - 24 will be 49% usable element and may be multiples of times cheaper to buy, than the former product.

MGS member.

 I have gardened in sub-tropical Florida, maritime UK, continental Europe and the Mediterranean basin, France. Of the 4 I have found that the most difficult climate for gardening is the latter.

David Bracey

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Re: NPK
« Reply #1 on: December 12, 2012, 03:07:09 PM »
Anita has asked me to reference this article.  The following appeared on the original Newsletter

"This is the condensed, shortened, abbreviated, concise, and summarized version of a three year course
in soil science.

Ian Powell, Tupelo Grove Nursery, Mylor"
MGS member.

 I have gardened in sub-tropical Florida, maritime UK, continental Europe and the Mediterranean basin, France. Of the 4 I have found that the most difficult climate for gardening is the latter.

*

Alisdair

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Re: Tupelo Grove
« Reply #2 on: December 12, 2012, 04:01:13 PM »
Ian Powell and Robyn his wife are superb plantsmen. We met them during the MGS October meeting in South Australia (and Robyn later escorted a lucky few of us on a fascinating side trip to Kangaroo Island).
Here is a couple of pictures of their Tupelo Grove, the second one being just a small part of their sales area - the Australians among us descended on this, full of choice of more or less drought-tolerant rarities, like a pillaging horde!
Alisdair Aird
Gardens in SE England (Sussex); also coastal Southern Greece, and (in a very small way) South West France; MGS member (and former president); vice chairman RHS Lily Group, past chairman Cyclamen Society

Trevor Australis

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Re: NPK
« Reply #3 on: December 13, 2012, 05:23:49 AM »
Ian Powell makes up his own NPK blend for Mediterranean plants (and gardens) which has less N than most proprietry brands. We are lucky to be able to buy it from the nursery and find it excellent. Ian produces it in a soluble mix and a prilled mix which is scattered on the ground and scratched in.
M Land. Arch., B. Sp. Ed. Teacher, traveller and usually climate compatible.

David Bracey

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Re: NPK
« Reply #4 on: December 13, 2012, 11:28:56 AM »
trevor, you are v popular to-day.  What is the ration of N in the NPK fertiliser.  Why do you want to reduce top growth?
MGS member.

 I have gardened in sub-tropical Florida, maritime UK, continental Europe and the Mediterranean basin, France. Of the 4 I have found that the most difficult climate for gardening is the latter.

David Bracey

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Re: NPK
« Reply #5 on: December 13, 2012, 11:33:12 AM »
I guess the answer is the the article

 "the Balance‖ may be 10 - 1.5 - 8 to suit the widest possible range of plants, the ornamental Mediterranean ratio may be more like 10 - 3 - 12 to have more steady growth from lower N, bigger root development from higher P and harder, stockier more flowery fruity plants from high K. The concentration of elements in the fertilizer bag is of no consequence i.e. 5- 1.5 - 6 and 10 - 3 - 12 and 20 - 6 - 24 are all the same proportions. Just make sure only as much element as the soil requires is used.

What ratio fertilizers do other members use.?

I tend to use whatever is available.
MGS member.

 I have gardened in sub-tropical Florida, maritime UK, continental Europe and the Mediterranean basin, France. Of the 4 I have found that the most difficult climate for gardening is the latter.

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Alisdair

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Re: NPK
« Reply #6 on: December 13, 2012, 12:58:43 PM »
On our heavy clay in Greece the only plants we fertilise are the citruses, and we now normally give them pure N (no P or K). They've not shown any sign of being short of the other two elements, but in one area where the limestone seems softer one or two of them occasionally look short of iron - quickly cured by watering in sequestered iron.
In France and UK we use a proprietary rose fertiliser on the roses, and here in UK (clay again) make up our own mixes for fruit trees and bushes but tend not to give fertiliser to anything else.
Alisdair Aird
Gardens in SE England (Sussex); also coastal Southern Greece, and (in a very small way) South West France; MGS member (and former president); vice chairman RHS Lily Group, past chairman Cyclamen Society