SOILS AND THEIR FERTILITY

A key factor in the growing of vegetables is an understanding of the make-up of the soil, its manuring and management. This is only learnt by< experience, but some basic information is detailed here. Soils contribute to plant growth by providing:

1. a source of water

2. an oxygen supply for roots

3. support and anchorage for plants

4. the essential nutrients for growth and development.

Different soil types are suitable for different vegetable crops:

SOIL TYPE

CROP

Heavy loam

Brussels sprouts Cabbage

Medium moisture-retaining loam

Broad bean

Beetroot

Leeks

Peas

Turnip & swedes

Silts

Onions

Medium to light loams

Lettuce Calabrese

Sandy soil

Carrot Parsnip

Peaty, moisture-retaining soils

Courgettes

Marrow

Celery

If one soil had to be selected for best all-round performance for’vegetable growing then a deep, fertile, well-drained loam would be preferred.

HOW TO IMPROVE THE SOIL

1. Organic Matter

Organic matter helps to bind soil particles together to form crumbs, increasing moisture retention, especially on sands. Bulky organic matter opens up the soil pore spaces on clay and stops the finer particles running together. The choice of organic matter may depend on what is available locally. Horse manure and farmyard manure are said to be the best. However, any type of manure is better than none at all. Beware of using too much chicken manure, which may be excessively high in nitrogen.

2. Liming

Lime is particularly useful on clay soils to help open up sticky, heavy land. Calcium is the major ingredient of lime, and is also an essential mineral element forv plant growth. Gypsum may be used to add calcium, and condition the soil without increasing pH (the measure of soil acidity).

3. Crop Rotation

Rotation is a valuable part of cropping, helping to maintain soil structure and to reduce the success of some pests, diseases and weeds.

Some crops help to improve the soil structure, their roots penetrating even the heaviest clay; leeks are surprisingly effective at this, as they grow well on a wide range of soils. Lupins are also grown for their deep penetrating roots and their nitrifying action.

Green manure crops (those turned in after growth) offer a valuable source of organic matter. Mustard, for example, sown at 1 ½ g/sq.m (16.5kg/ha) will mature in 8 weeks in the summer.

DRAINAGE

Waterlogging of soils causes the pore spaces to fill up with water. This excludes air essential to roots and encourages the rearrangement of soil particles. It may bring silts to the surface. The drainage may be improved by:

a) incorporating organic matter

b) regular liming

c) crop rotation

d) under many fields there is also a clay pipe drainage system, which helps to control the water-table (the natural level of free water in the soil).

By carrying out these measures good soil structure can be maintained, provided cultivations are carried out at the correct time.

CULTIVATING THE SOIL

1. Deep Cultivation

This is desirable with practically all vegetables. Heavy soils should be ploughed, cultivated or dug in autumn, light soils in late winter or early spring. Ideally, once every 3-4 years, carry out double digging in order to break up the compacted subsoil layer which may have formed below the depth of digging. This increases the depth of rooting and the quantity of water and nutrients available to the crop.

2. Bed Systems of Cultivation

This is where soil is thrown up to form beds, which are separated by permanent paths.

The advantages of this system include:

a) Potentially higher yields/unit area (than for open ground).

b) Cultivation of the bed area only, not the paths.

c) All work is carried out from the path, thus preventing damage to the structure of the soil in the raised beds.

d) Any weed growth on the path areas is easily controlled by cultivation, weedkillers or mulches.

3. Crop Rotation

The idea of crop rotation has long been practised by gardeners. It involves changing the position of crops each year so that the same crop does not occupy the same ground in consecutive years. Usually the rotation is carried out on a three-year basis, the order of crops often being legumes, followed by brassicas and then root crops.

The advantages of rotation

Rotation limits pests, diseases and some weeds. If related vegetables are grown on the same piece of land every year, certain soil pests and diseases can build up to a damaging level.

Examples of specific problems which a good rotation may help to contain:

CROP DISEASE PEST

Roots Parsnip canker Carrot cavity spot Club root of swedes /turnips Keeled slug Spotted millipede Cutworms Wireworms

Potato Powdery scab Wart disease Common scab Potato blight Mosaic virus Potato cyst eelworm Keeled slug

Pea/Bean group

Foot rot Chocolate spot in broad beans

Pea moth Pea thrips Black bean aphid

Brassicas

Club root

Cabbage root fly Brassica white fly

Onions

Onion white rot

Onion fly

A BROAD GROUPING OF CROPS FOR A FOUR-YEAR ROTATION

ROOT GROUP

(Light feeders – soil previously manured or well composted)

ONIONS & BRASSIGAS

(Heavy feeders – rotted man(ure applied during winter. Lime if required after autumn cultivation)

Beetroot

Carrots

Chicory

Endive

Parsnip.

Radishes

Salsify

Scorzonera

Spinach

Swedes

Turnips

Broccoli

Brussels sprouts Cabbage. Cauliflqwer

Chinese cabbage Kale

Kohlrabi Radishes Garlic Leeks

Onions

Shallots Spring onions

POTATO GROUP

LEGUME GROUP

(Well-rotted compost) (compost of leaf mould type)

Capsicums Courgettes Cucumber Lettuce Marrows / Potatoes Swiss chard Spinach beet Sweetcorn Tomatoes s

Broad beans

French beans

Haricot beans ,

Peas

Runner beans

Celeriac

Celery

Jerusalem artichokes

Stick beans are often grown on a single, permanent site where soil fertility is raised by extra-deep soil cultivation and manure/compost applications every year.

A FOUR-YEAR ROTATION

The basic rotation can be as follows when the plot is divided into 4:

YEAR

1. Potato group 2. Legume group 3. Onion & brassica group 4. Root group

YEAR

1. Legume group 2. Onion & brassica group 3. Root group 4. Potato group

YEAR

1. Onion & brassica group 2. Root group 3. Potato group 4. /. Legume group

YEAR

1. Root group 2. Potato group 3. Legume group 4. Onion & brassica group

If strawberries are to be included, a five-year rotation should be used. A green manure can follow early roots or early potatoes.

There are many variations on this basic theme, and the grower or gardener selects a scheme to suit the circumstances.

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