Besides an examination of the natural vegetation referred to at p. 90 the experienced plant-grower will also make a physical or mechanical examination. He will handle the soil, feel its texture, noting its colour and whether its particles cleave together or fall asunder and crumble into dust; and if he is wise he will also have a good-sized hole dug out to a depth of 3 or 4 ft. so that he may see the geological formation. He will then be able to form a good opinion as to what may be done with the land. If the vertical section of the hole shows a good depth of yellow loam resting on sand, gravel, or chalk it is a good sign. Such a soil will contain plenty of plant food, may be easily, deeply, and economically worked, will not require large quantities of manures, will not be too dry or too hot in summer, nor too cold or too wet in winter, and will respond readily to good cultural practice.

It follows that any other soil which does not approach this ideal is less valuable and may cost a good deal more to cultivate.

To gain a fairly accurate idea as to the physical condition of a soil a fair sample of it should be taken from the first, the second, and the third spit down. A cubic foot of each might be taken and weighed. This multiplied by 43,560 will be the weight per acre. A certain quantity of soil, say 10 oz., should be spread out and allowed to dry in the sun and air. Weigh again, to see how much moisture has escaped, and compute the amount per acre. After air-drying and noting the amount of water given off, the samples should then be baked over a fire until all the organic material is driven off by combustion into the atmosphere. In this way the carbon, oxygen, hydrogen, and nitrogen will be liberated, and the residue will represent the mineral substances which cannot be further reduced. Then pass each sample through a sieve with an 1/8-in. or 1/4-in. mesh, so as to take out all the larger stones. Weigh these also and compute for the acre. The finer soil left should be mixed with water in a glass vessel and well churned up with a stick; hot water will free the finer particles better from the sand and gravel than cold. All the fine clayey particles will remain suspended in the water and make it muddy, while the sand and grit will fall to the bottom. By pouring off the muddy water time after time, until at last the water is quite clear, the mud or clay will be separated from the sand. Allow to settle, pour the water off carefully, and when sand and clay are dry they can be weighed. The result will show the proportion of each in the sample, and the weight may be computed for the acre.

The weight of a cubic foot of soil of various kinds in a dry and wet state, and the amount of water each contains, have been computed as follows by M'Connell in his Notebook of Agricultural Facts and Figures: -

Kind of Soil.

One Cubic Foot Weighs.

Amount of

Water in One

Cubic Foot of

Wet Soil.

In Air-dry State.

In Wet State.

lb.

lb.

lb.

Siliceous sand ...

111.3

136.1

27.3

Calcareous sand...

113.6

141.3

31.8

Sandy clay

97.8

129.7

38.8

Loamy clay

88.5

124.1

41.4

Pure grey clay ...

75.2

115.8

48.3

Humus ...

348

81.7

50.1

Garden mould ...

67.8

102.7

48.4

The mechanical constitution of a good garden soil for the production of most fruits, flowers, and vegetables might be stated thus, and assuming that an acre of soil at 1 ft. deep weighs 3,000,000 lb.: -

Clay, 40 per cent = 1,200,000 lb. per acre.

Sand, 35 „ = 1,050,000 „ „

Lime, 10 „ = 300,000 „ „

Humus, 15 „ = 450,000 „ .

These figures may be compared with the following analysis of a fertile soil on the same basis: -

Per Cent.

Lb. per Acre of 3,000,000 lb.

Potash

103

30,000

Soda ...

1.97

60,000

Ammonia

.06

1,800

Lime ...

409

120,000

Magnesia

13

3,900

Peroxide of iron

9.04

270,000

Protoxide of iron

.35

10,500

Protoxide of manganese

.29

8,700

Alumina

1.36

40,800

Phosphoric acid

.47

14,100

Sulphuric acid

.90

27,000

Carbonic acid...

6.08

180,000

Chlorine

1.24

37,500

Soluble silica ...

2.34

70,200

Insoluble silica clay Insoluble silica sand

57.65

1,729,520

Organic matter (humus)

12.00

360,000

Water or loss...

1.00

30,000

The grower should avoid a purely sandy or gravelly soil, because it will empty his purse in purchasing manure and supplying water; and he should shun a wet, heavy, sticky yellow clay such as is suitable for the making of bricks and pottery, because it would require large funds and many years of cultivation to induce such a soil to bear even reasonably good crops. The very worst soils can be brought into a state of fertility in time, but it will never pay the commercial horticulturist to waste his time upon them.

A man need not be a chemist to be able to distinguish the differences between a sandy, loamy, peaty, chalky, or clayey soil, and although each one contains essential plant foods in varying proportions it would be a mistake to assume that they are all equally valuable or available.

These remarks relate chiefly to the soil when it is to be worked in a natural condition by the grower of fruits, flowers, and vegetables in the open air. Although the grower under glass is not hampered so much with the natural soil and the weather, it is nevertheless to his advantage to select the best possible soil on which to erect his glasshouses, especially if he intends to embark on the culture of such crops as Grapes, Tomatoes, Cucumbers, Peaches, Nectarines, or any other crop which is to root in the natural soil. For Melons, Ferns, Cyclamen, Chrysanthemums, Carnations, Bulbs, Zonal Pelargoniums, Heaths, Marguerites, Roses, and many other crops, soils have to be brought in and mixed in various proportions before use. The labour and expense of these operations are great, in addition to which large sums have to be spent on the erection of greenhouses and heating apparatus, the purchase of pots, etc.