" experimentation 60

PART II.--PRINCIPLES OF MANURING.

CHAPTER I.--FERTILITY OF THE SOIL.

What constitutes fertility in a soil 65
I. Physical properties of a soil 66
Kinds of soils 67
Absorptive power for water of soils 67
Absorptive power for water of sand, clay, and humus 68
Fineness of particles of a soil 69
Limit of fineness of soil-particles 69
Importance of retentive power 70
Power of plants for absorbing water from a soil
experiments by Sachs 73
How to increase absorptive power of soils 74
Amount of water in a soil most favourable for plant growth 75
Hygroscopic power of soils 75
Capacity of soils for absorbing and retaining heat 76
Explanation of dew 77
Heat of soils 78
Heat in rotting farmyard manure 78
Causes of heat of fermentation 79
Influence of colour on heat-retaining power 80
Power of soils for absorbing gases 81
Gases found in soils 81
Variation in gas-absorbing power of soils 82
Absorption of nitrogen by soils 82
Requirements of plant-roots in a soil 83
Influence of tillage on number of plants in a certain area 86
Comparison of English and American farming 86
II. Chemical composition of a soil 87
Fertilising ingredients of a soil 87
Importance of _nitrogen, phosphoric acid_, and _potash_ in a
soil 88
Chemical condition of fertilising ingredients in soils 89
Amount of soluble