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Updated : 21/9/2014

Identifying a Soil Problem

Cracked Soil Photo: iStock

In a well-composted garden soil, mineral deficiencies are unlikely to occur. However, deficiencies in trace elements can occur in Australia and South Africa as their soils are ancient. To help combat this, incorporate a range of organic fertilisers, such as seaweed, plus compost into the soil to provide high levels of plant nutrition and adequate trace elements.
Many diseases, especially viruses, cause symptoms that can easily be mistaken for nutritional problems, which are often difficult to diagnose. Temperature extremes and irregular watering also cause symptoms that may appear to be nutritional.
Excessive liming of soil or markedly acidic soils can cause mineral elements in the soil to be unavailable to plants. Always check your soil pH first. Select crops best suited to your soil and climate. Also, crop rotation helps to ensure that excessive nutrients are not withdrawn by particular crops.


 

Element Deficiency symptoms Probable cause and remedy
NitrogenGrowth is poor; shoots are short; leaves are small; and yellow brassicas turn pink then orange. Fruit or tubers
are small.
As an immediate booster, spray with diluted liquid
seaweed or fish fertiliser. Incorporate as much compost
and manure as possible.
 

Phosphorus
Root development and flower bud formation are poor, and plants sometimes also show symptoms similar to that of nitrogen deficiency. Brown spots may appear on leaves, or leaf edges may turn brown. Fruit has an acid flavour. Bonemeal is rich in phosphorus. Incorporate 120 g per square metre before planting. The deficiency appears more often in acid soils.
PotassiumGrowth becomes stunted, and leaves turn a dull bluegreen, with browning at the leaf tips or leaf margins, or showing as blotches. Leaves of broad-leaved plants
curl downwards.
Most often seen on light, sandy soils. Comfrey tea is high in potassium; dilute 1 part tea to 15 parts water and apply to soil. Wood ash is high in potassium.
MagnesiumMagnesium deficiency shows either as a loss of colour or as a mottling of red, orange, brown and purple tints. Excessive potash application may be responsible. Spray with a solution of Epsom salts (250 g in 12 litres water).
If liming soil, apply dolomite, which is rich in magnesium as well as calcium, or green sand.
ManganeseManganese deficiency occurs in sandy and alkaline soils, frequently in combination with iron defi ciency. Chlorosis (loss of colour) begins on older leaves. The leaves of green peas develop brown patches. Beetroot leaves have red-brown speckling. This is most evident in poorly drained soils. Lift beds to
improve drainage. Overliming can also be responsible. Never apply manganese to soils with a pH below 6.

Iron
Chlorosis (loss of colour) occurs on young shoot tips and leaves, while the veins remain green. Eventually, shoots die back. This condition usually occurs in alkaline soils,
which prevent plants from absorbing iron.
Sequestered iron (iron EDTA) used as a foliar spray produces rapid results. Check soil pH and acidify with sulphur and regular compost additions.
BoronThe roots of beetroots, swedes and turnips turn brown. Cauliflower curds also turn brown. Brown cracks appear across the stalks of celery. Apple cores become ‘corky’. The growing points of plants die off. Mix 30 g borax with sand and disperse evenly over 18 square metres of soil. Or spray crops fortnightly with liquid seaweed fertiliser. Overliming can cause
this problem.

Molybdenum
Leaves, particularly of broccoli and cauliflowers, develop a disorder known as whiptail. Leaves become distorted and shrink back to the midrib, giving a tail-like appearance. On tomatoes, leaves become mottled and roll forward. Apply ground dolomite to acidic soils. Add kelp meal to soil. For a short-term remedy, apply sodium molybdate at 30 g per 8 litres water. This will treat 8 square metres of soil.
CalciumThis shows most commonly in tomatoes and capsicums as a darkened, shrivelled end on fruit. It also causes bitter pit in apples. Uneven soil moisture causes a failure of calcium uptake from the soil. This is particularly evident in pot-grown plants and in light soils. Water regularly. To add calcium,
incorporate crushed eggshells into compost.
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