Monday, 13 April 2015

Minerals and plants

I've been doing some research into minerals and plants. I want to make sure the soil I've revealed from under all that concrete is now capable of being as productive as possible and I've found out a few things about how vitally important minerals are in keeping plants healthy.

Some key elements are calcium, magnesium, sulphur and silicon:

Calcium (Ca) - this element is linked to the pH of your soil, with higher pH soils usually containing more calcium. Calcium in plants is used in cell walls. Calcium deficiencies tend to be caused by a disruption in the supply, rather than a shortage in the soil. Causes can be a shortage of water (calcium is carried in the water the plant draws up) or excessive use of potassium or magnesium fertilisers. Calcium deficiencies cause blossom end rot in tomatoes and bitter pit in apples. They can cause die back or burn marks on young leaves and they lead to a loss of apical dominance.
Magnesium (Mg) - essential component of chlorophyll production and as a result is important in gaining high photosynthesis ability. High photosynthesis ability is key in increasing plant health and ability to resist pest and disease attack and also in increasing drought resistance. A deficiency of Mg shows up as green veined leaves with yellow between the veins. Found on older leaves first. Easy to confuse with virus attack and natural aging. Can be a problem caused by waterlogging, lack of water and compacted soils. Can also be caused by too much potassium being added to the soil or plant.
Sulphur (S)  - helps the plant to form important enzymes and plant proteins. Deficiencies cause yellowing of leaves, with oldest and highest leaves yellowing first. It is rare to find a sulphur deficiency.

Other trace elements include boron, iron, manganese, molybdenum, sodium, copper and silicon.

Boron (B) deficiency is one of the most widespread micronutrient deficiencies around the world. Boron is found in cell membranes. It affects the stability of cell walls as well as the ability of plants to take up other nutrients. It is particularly important in flower and fruit development. It is also important for photosynthesis as it affects the ability of plants to transport sugars away from the site of photosynthesis to where they are needed - for plant growth, fruit development, root growth and as root excretions. Sugars need to keep moving like this in order for photosynthesis to continue. Boron is also used in the development of root nodules in nitrogen fixing plants. It is also used in protein synthesis. Deficiencies in boron lead to poor plant growth and loss of fertility. Only very small amounts of boron are needed by plants. Too much is actually toxic, so efforts to increase boron need to be very careful about it.

I've been looking at different ways of increasing mineral availability to plants, including the use of mineral accumulators (or dynamic accumulators), foliar feeds and general soil mangement.

Mineral accumulators are plants that draw up minerals from the soil, accumulating them within their leaves - elements such as magnesium, copper and iron. These minerals can be made available to other plants by using the cut leaves as a mulch or by adding them to compost.

Here is a list of some plants and the elements they accumulate, with elements listed in order with higher concentrations first and with elements of significantly high concentrations compared to other plants listed in bold type.

Key plants:

Fat Hen (Chenopodium album) K, P, Ca, (also a little Fe and Na). Has extremely high levels of K. Has very high levels of P and Ca.
Amaranth (Amaranthus spp) K, Ca, P, Mg, Na, Fe (also a little Cu). Has pretty high concentrations off all these elements (except the Cu), especially Ca and K. Mg and Na are also present in relatively very high concentrations compared to a lot of other plants.
Stinging Nettle (Urtica dioica) P, S, Ca, N, K, Mg, Si Cu and Mo (also a little B). All the elements listed in bold are in higher concentrations than a lot of known mineral accumulators. Mg is also in relatively high concentrations compared to other plants.
Dandelion (Taraxacum officinale) K, Ca, Na, Fe, P, S, Mg, B, Mn (also Cu). Has much higher concentrations than a lot of other plants of B and Fe. Also high concentrations of Na, K, Ca and Mn.
Red Clover (Trifolium pratense) Mg, Mn (also B and Cu). Significantly high concentrations of Mg and Mn.
Lambs Lettuce (Valerianella locusta) K, Ca, Fe, Mg, B (also Na, Mn, Cu and Mo). Particularly high levels of B - one of the highest on record. Also very high levels of Fe and quite high levels of K.

Other useful plants:

Yarrow (Achillea millefolium) K, Ca, Mg (also a little Na, Mn and Si).
Borage (Borago officinalis) K, Ca
Feverfew (Chrysanthemum parthenium) K, Ca, Mg (also a little Mn, Na and Si)
Chicory (Cichorium intybus) K, Ca, Mg, Na (also Fe)

Sometimes minerals are readily available in the soil, but something is stopping plants from being able to access them. Careful management can stop this from being a problem. For example:
  • Improve heavy soils to make their rich nutrients more availble - add organic matter. Potentially add lime (or calcified seaweed) to encourage large particles to break down into smaller ones.
  • Shortage of water in the soil reduces mineral uptake - maintain a steady water supply and/or add organic matter to the soil and a mulch on top to retain water in the soil for longer.
  • Root damage by pests, diseases or waterlogging may make a plant unable to take up the food it needs. Add organic matter to the soil to improve drainage.
  • Too much fertiliser or lime can make some nutrients unavailable to plants. Be careful to only add food supplements if they are needed.

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