Chrysanthemums in Aberdeen
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 Chrysanthemum
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Common Pests:
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Aphids
- Thrips
- Leafminer
- Earwigs
- Slugs 
- Whitefly
- Capsid Bug
- Caterpillars
- Red Spider Mite
- Vine Weevil
- Sciarid Fly
- Stool Miner

Common diseases: 
- White Rust
- Verticillium Wilt
- Powdery Mildew
- Crown Gall
- Chrysanthemum Rust
- Botrytis

Common disorders:
- Nitrogen 
- Phosporus
- Potassium 
- Magnesium
- Manganese
Boron
- Copper
- Iron
- High Salt levels

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Date last updated: 
10 July 2008

 

Nitrogen (last updated 10 July 2008 )

Nitrogen is the nutrient most needed by plants, it helps them produce bulky growth and is the most likely to be deficient from soils if not added as fertiliser because as nitrate it leaches quickly from soils. Nitrogen in the form of organic matter and ammonium ions has a positive charge and stick to clay particles, clay particles have a negative charge. When soil bacteria break them down into nitrates they have a negative charge and repel from the clay particles and then become freely available to plants. Because nitrates are mobile in the soil they easily reach roots and are quickly taken in by roots, they also are easily leached from soils.

Other matters affecting the availability of Nitrogen (N) 
At a pH of 6 to 7.5 nitrogen is freely available, when the pH drops below this figure nitrogen fixing bacteria do not thrive and therefore cannot convert organic nitrogen to ammonium and ammonium to nitrates.

Flooded or saturated soils hold little oxygen, oxygen is necessary for all aerobic bacteria to function. Soils that dry out and rewetted have a tremendous bacterial activity, therefore this is the sort of soil condition we should encourage to get good nitrogen conversion. 

Temperature is another factor, the metabolism of micro organisms increase in warm soils. So organic nitrogen does not convert to nitrates in cold soils. (winter) neither does ammonium nitrogen convert into nitrate nitrogen. 

As an example the results of a soil test in an organic rich soil will vary depending on the conditions available to break the organic matter down. If you think about it, organic matter breaks down more efficiently in top soil where oxygen is present than in subsoil where there is very much less oxygen. Therefore the correct amount of air to water ratio is important for the conversion of nitrogen. For plant roots to take in ions they gain their energy from sugars and other compounds supplied by the phloem system, this is made in the leaves as a result of photosynthesis. 
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awaiting picture
They also need Oxygen from the soil air so that the roots can respire. Therefore non-compacted soil is essential. During periods of very wet weather leaves appear pale, the absence of soil air and the reduction in transpiration reduces the amount of nitrogen ions (amongst others) that are taken in by the plant and therefore the plant appears pale in colour. 

N & P are used to synthesise proteins and DNA that the cells need to survive. They are needed in large quantities to produce good plant growth. 

Mild nitrogen deficiency can cause leaves to be pale green and growth to be checked. A severe deficiency will result in stunted growth and pale yellow-green foliage. Leave size is reduced and youngest leaves remain erect. Only the youngest leaves darken when buds become visible. Flowering is delayed, bloom size reduced and sprays develop fewer blooms than normal. 

A mild excess of nitrogen causes very dark green leaves and delayed flowering. Severe nitrogen excess may cause root damage and subsequent poor growth. Leaves are very dark green and plants wilt easily. In extreme cases the symptoms are very similar to iron deficiency. 

Remedial Actions
To resolve nitrogen deficiency feed with a soluble high nitrogen fertilser such as sulphate of ammonia.

Excess nitrogen can be reduced by flooding in order to leach away the excess, however be aware that waterlogging in a retentive medium may make matters worse.


Other information 

 

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Copyright 2008 Paul Barlow.