R2102 – nutrients

Nutrients are taken up by plants through the roots with water. You will need to know which ones are major nutrients and which ones are minor. The nutrients and what they are for and how deficiency shows:

Major nutrients

• Nitrogen (N) = needed for growth of stems and leaves. It is used to make chlorophyll. If deficient, the leaves go yellow, starting with the older leaves. Growth is also slow.
• Phosphorus (P) = needed for root growth. It is used to make proteins and enzymes used in respiration. If deficient, growth is slow, leaves are a dull colour and flowers and fruit are small.
• Potassium (K) = needed for fruit and flowers. If deficient, fruits and flowers are poor, older leaves roll inwards and down, with scorching around the tips.
• Calcium (Ca) = a major component of cell walls. If deficient, cell walls are weak, leaves curl inwards eg: blossom end rot in tomatoes.
• Magnesium (Mg) = needed for photosynthesis as a component of chlorophyll and for the movement of phosphorus. If deficient, yellowing between the veins of the leaves (intervein chlorosis)

Minor nutrients

• Iron = needed for production of chlorophyll and enzymes. If deficient, intervein chlorosis is seen affecting the younger leaves first.
• Manganese
• Zinc

Soil pH

Soil pH can have an affect on whether the nutrients can be taken up by a plant. Acidic soils restrict Nitrogen, Calcium and Phosphorus; whilst alkaline soils restrict Iron, Manganese and Zinc. Lime-induced chlorosis is where the pH is too high or alkaline and iron is restricted causing yellowing leaves. A soil pH of around 6.5 is balanced and most nutrients are available. This soil pH also encourages earthworm and bacterial activity since they can be reduced in acid soils.

However, some plants can be adapted for acidic soils (calcifuge plants) because they originally come from countries with acidic soils. Others are adapted for alkaline soils ( calcicole plants), and there are some which have a neutral soil preference. You will need to know a few examples of each:

Acidic/calcifuge pH 4-6	Neutral	Alkaline/calcicole pH 7-8
Rhodedendrum	Malus	Clematis
Camellia	Cucumber	Dianthus
Erica	Daucus carota	Scabious
Magnolia	Paeonia	Viburnum

Soil pH can be altered, although it is expensive and time-consuming and in general, it would be better to work with and select plants suitable for the soil pH you have.

• Lime – adding lime or calcium carbonate to raise the pH (make it more alkaline). There are tables to work out how much should be added to get to pH 6.5. It is added months before any plants are added to the ground and should be applied carefully whilst wearing gloves and perhaps a mask as it is a fine powder. Liming the soil can also affect the structure of the soil, aiding crumb formation.
• Sulphur – added to lower pH to make the ground more acidic. This takes years to lower the pH and is is very rare that this is ever done.
• Organic matter – compost holds on to nutrients making them available to plants.

pH is a log scale measuring the number of hydrogen ions present. The scale runs from 1 to 14, with 1 being the most acid and 14 being the most alkaline. Neutral is 7. The range found in soil is 4 to 8.

Fertilizers

These are things added to the soil which contain high levels of nutrients. They can be organic – coming from organic sources, such as bonemeal or comfrey; or inorganic – coming from an industrial process, such as Growmore, Osmocote and ammonium nitrate [learn these 3 names]. Organic fertilizer have the benefit of being minimally processed, sustainable, nutrients are unrefined and “natural”, slow-release and sustain soil life.

The different types of fertilizer are:

• soluble/quick release = dissolving in water and watered in to the soil so that the nutrients can be taken up immediately eg: ammonium nitrate. Care needs to be taken that it is not too strong, as water could be drawn out of the plants roots by osmosis because the concentration gradient is the opposite to what is needed if it is.
• slow release = provides nutrients slowly over a period of time eg: bonemeal. This might not have broken down and be available when the plant needs it though.
• straight = only one compound eg: nitrogen
• compound = provides a mix of nutrients eg: Growmore
• controlled release = releases nutrients over a particular timescale eg: Miracle Grow continuous release plant food

Fertilizers can be applied as

• base-dressing – where the fertilizer is worked in to the soil before planting
• top dressing – where the fertilizer is applied to the surface of the soil. This is used for established plants
• liquid feed – where the fertilizer is dissolved in water the watered in
• foliar feed – a very dilute solution which is sprayed on to the leaves. This has immediate uptake and is good for deficiencies.

Nettle and comfrey tea

You are required to know how to make nettle and comfrey “tea” fertilizers for the exam. The method for making both is the same. Nettles have very deep roots, allowing them to take up nitrogen from deep down in the soil, so nettle tea is a high nitrogen feed. Comfrey tea is a high potassium feed.

You make the teas by cutting up the leaves of either nettle or comfrey and placing them in a bucket. Cover the leaves with water and then cover the bucket and leave it somewhere warm, but far away from the house because it really smells! Stir the mixture every day and after 2 or 3 weeks, it is ready and can be drained off. It is diluted at 1 part tea to 10 parts water and used as a feed.