Nutrient Deficiencies can be a difficult thing to diagnose absolutely in a plant.
Nutrients (also called elements or fertilisers) are either mobile OR not-mobile
Mobile Nutrients are ones that move through the plant (ie are mobile) making ALL the plant the same colour. A plant therefore that is Nitrogen (N) deficient will be uniformly LIGHT green.
Some nutrients that are mobile are:
- Nitrogen (N)
- Magnesium (Mg)
- Potassium (k)
- Chlorine (Cl)
- Molybdenum (Mo)
Non- mobile nutrients
These nutrients do NOT move through the plant so show up the deficiency in the NEW leaves (ie the leaves produced AFTER the plant experiences the nutrient deficiency). A plant with Iron (Fe) deficiency will have pale NEW leaves (an extreme Iron deficiency will have white new leaves due to lack of chlorophyll as Iron is needed to make chlorophyll) but the rest of the plant will still be dark green.
Some nutrients that are NOT mobile are:
- Boron (B)
- Calcium (Ca)
- Iron (Fe)
- Manganese (Mn)
- Sulphur (S)
A plant may be deficient in one nutrient & when that deficiency is corrected then a second deficiency may show up. The second deficiency may display only slight symptoms so may just seem to not grow as well and not show typical deficiency symptoms. This is the reason why it is more practical to apply a “shot-gun” fertiliser that contains a bit of each of the usual micro nutrients that are likely to be deficient.
Just repeating what I have said before, a plant can take up any nutrient only in solution & that nutrient needs to be in an AVAILABLE form. A great example of this is the soil found in the Toowoomba region. The red soil is red because of the high Iron content, but an Iron deficiency still is common because the Iron is chemically locked up and NOT available to the plants.
A list of other nutrient problems that may occur:
- Excess nutrients The nutrient may be in excess and therefore available in toxic amounts. This can be because too much of the nutrient is available at one time. EG: If a fast release (soluble) fertiliser (like Urea) is used but left without being washed in so the next time it rains or the garden is watered a bit, then a lot of the fertilizer is available in toxic amounts in the root zone & so causes fertiliser “burn”.This often occurs when a bit of the fertilizer is lodged where the leaf joins the stem, gets wet then releases too much nutrient which then draws out the cell sap (as the fertilizer has a higher chemical strength than the cell contents) & the part of the plant that is in contact with the excess fertilizer is killed.
- Too high or too low pH & so the nutrient is there but NOT available to the plants.
- Fungi or bacteria attack. Either of these will break down the plant’s outer protective layer & allow entry of either bacteria & or fungi. This may look like a nutrient deficiency.
- Insects eating the plant. This will also open up the plant to looking like a nutrient deficiency.
- What looks like a disease but is really a nutrient deficiency. A great example of this is in tomatoes with the “disease” called Blossom Rot. It is NOT actually a disease but a Calcium (Ca) deficiency. Once the fruit show these symptoms it is too late for that fruit but by adding Calcium to the soil the next fruit will usually be free of the problem.
- Herbicide effect. This may be over the whole plant but may also be on only a few leaves if it is a contact-only herbicide. If the herbicide is quite weak then there may be only slight symptoms.
- Fluoride toxicity. This does not usually occur but may if excessive amounts of fluoride have been added to the town water supply (by human error)
- Excessively high or low temperatures. The leaves can be burnt by excessively high or low temperatures or if a plant is exposed to these temperatures too quickly without being slowly exposed to them from being in a sheltered place such as under a dark shad-cloth.
- Salinity. This may be from water that is too high in salt (Sodium Chloride) from irrigation water, salt spray or some fertiliser (eg Potassium Chloride)
- Time of the year. Gardenia’s sometimes in Spring show Iron deficiency due to too low a temperature in the winter that does not allow the plant to take up enough Iron.
- Water logging. When the soil is full of water there is not any oxygen in it so the plant’s roots cannot breathe & adsorb any nutrients.
- Drought. With not enough water then the plants cannot take up any nutrients in solution.
- Toxin in the medium. There may be too much tannin in the bark & or potting mix as it has not leached out before it was bagged.
- Excessive wind. Windburn can look like a nutrient deficiency such as wind burn from being in a open truck while being moved and not covered.
- Air pollution. From being next to an industrial site where toxic fumes are being emitted.
So if you are not sure what is causing your nutrient problem add an all rounder fertiliser to correct the problem as it can be difficult trying to establish exactly what the deficiency might be without expensive and most likely unnecessary soil testing. Or use your Compost making sure your ingredients in your Compost heap come from many different sources or it too may be lacking in a particular nutrient.
Today’s Did You Know…?
It is desirable to grow plants (including lawn) next to a house on heavy clay soil such as what you might find in the Darling Downs. The ground is usually kept moist because you are watering your garden all the time, so that the clay is kept expanded and does not crack any solid building material eg bricks or Besser blocks. Timber can move a little to accommodate any soil movement so is not as likely to crack. Turf would keep the soil under it moist, shaded from the direct sun & reduce any reflected heat. Green couch is a good grass to use as it does all the above plus is highly salt tolerant. It is good near the ocean as well with salt spray being carried on the wind. But if the clay dries out then you get cracks in your brick work or plaster.