PLANT NUTRITION

It is important to understand that all vegetables require a supply of nutrients. Of these the most important are nitrogen, phosphate and potash.

The main questions to ask are:

i) What are the best sources of these nutrients?

ii) In what quantity are they required?

iii) When should they be applied?

Nitrogen promotes vigorous dark-green growth in vegetables, and is of greatest benefit to all green crops and other leafy vegetables e.g. lettuce, celery and spinach.

Sources of N

Inorganic – Sulphate of ammonia Contains 15-23% N

Nitro chalk

Nitrate of soda

Organic – Dried blood

Hoof & horn

Farmyard manure

Quick-acting.

Gives a steady supply of N throughout the season.

Helps soil structure and water retention as well.

Sulphate of ammonia and nitrate of soda are usually applied at about 33g/sq.m (1 oz/sq.yd) either before sowing, or 10-14 days after sowing or planting, or during the growing period of the plant.

Phosphate stimulates the development of seedlings by encouraging a fibrous root system. It hastens maturity and increases yields – particularly of root crops.

Sources of P

Inorganic – Superphosphate

Organic – Bone meal Use sterilized bone meal

Superphosphate may be raked into the seed bed before sowing, usually at a rate of 50g/sq.m (1 ½ oz/sq.yd).

Potash maintains balanced growth in vegetables and helps plants resist adverse conditions e.g. poor light, shallow soil and severe winter weather.

Source of K Note

Inorganic – Sulphate of potash

Muriate of potash Not equally suitable

for all vegetables.

Organic – Manures e.g. farmyard manure

The normal rate of application is around 33g/sq.m (1 oz/sq.yd).

Many of the compound fertilisers which contain N, P and K can be used in the vegetable garden, e.g. Growmore. A general mix which can be used as a base dressing colild include:

1.8kg (4 lbs) – Sulphate of ammonia 2.2kg (5 lbs) – Superphosphate V 0.9kg (2 lbs) – Sulphate of potash

These fertilisers should be raked in well a fortnight before sowing or planting, at the rate of 100g/sq.m (3 oz/sq.yd).

There are a number of proprietary liquid feeds which can be watered on during the growing season. These give speedy results.

Liming

Continual cropping, and the addition of compost and manures, may make the soil rather acid. To counteract this apply a dusting of lime in winter – 106g/sq.m (3 ¼ oz/sq.yd). Avoid over-liming, as this will not help growth. One can test the pH by using a proprietory soil-testing kit.

pH Crop/soil acidity tolerance

7.0 asparagus, radish

6.5 cauliflower, spinach

6.0 lettuce, leek, onion, parsnip

Critical levels of tolerance

5.8 beans, peas, brassica, carrot, celery / 5.0 cucumber, marrow, tomato, sweetcorn

Some soils are naturally free from particles of chalk or limestone, and the local flora will probably include heather, rhododendrons and bilberries. These soils are likely to benefit from the use of lime in the vegetable garden.

In other parts of the country, the Salisbury Plain and the

Mendips for instance, -much of the mineral soil is composed

of fragments of (CaCO2) – the chalk/limestone group which

neutralise acidity ctrrd make soil alkaline (pH over 7). Some

plants do not cope well with high pH conditions and their

leaves may become golden or ivory-coloured in the absence of

the essential chlorphyll (green) structures. Such plants’

decline rather than thrive.

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