The Value of Soil Analyses to the Farmer. 3 



provides the plant with certain foodstuffs but also with water 

 and air, and the character of these supplies goes more to deter- 

 mine the crop than anything else. For example, we all know of 

 how little avail even the best manured land is in a drought ; it 

 is then far more important that the land should have been well 

 cultivated and properly managed, because upon these operations 

 depends the success with which the plant will obtain whatever 

 water is available. Again, some soils are known to hold out 

 against drought better than others, the difference cannot be 

 a chemical one but must be due to some inequality in their 

 capacity to retain water falling as rain or to lift that which lies 

 in the sub-soil below. If, again, we consider the wheat crop 

 of the past season, it was very noticeable that after the excessive 

 rainfall of the previous winter there were on most soils patches 

 where the wheat was stunted and of a bad colour, patches 

 which never afterwards caught up with the rest of the field. 

 These patches in nearly all cases owed their existence to some 

 interference with the air supply in the soil ; either from its close 

 texture or lack of drainage the soil below these spots for some 

 little time became saturated with water to the exclusion of air, 

 whereupon followed the death of the roots and the destruction 

 of some of the most valuable elements of plant food. 



Now one way of looking at a soil whereby some estimate 

 may be formed of its behaviour towards water and air is to 

 submit it to a mechanical analysis which will grade it into 

 groups of particles of particular sizes. From this point of view 

 all soils are mixtures of little particles — some large like sand, 

 which, whether coarse or fine, possess no coherence but fall 

 into a loose powder when dry ; some much finer, so as to be 

 scarcely gritty between the fingers ; and some so fine that they 

 will hang in water like a cloud for many hours, are quite soapy 

 to the touch, and cohere firmly on drying. Coarse sand lies at 

 one end of the scale, the finest pipe clays at the other, but it 

 should be borne in mind that the coarsest sandy soil will always 

 contain some fine sand, silt, and clay, while the purest natural 

 clays are not free from sandy admixtures. Just as one could 

 grade a gravel deposit into two inch, inch, half-inch and quarter- 

 inch material, the process of mechanical analysis separates, 

 partly by sieves but chiefly by settlement from water, the soil 

 into fractions of known size, these fractions being arbitrarily 

 selected but possessing certain characteristic, if not sharply 

 defined, differences of behaviour. 



The result of the mechanical analysis gives precision and 

 reduces to figures the farmer's way of considering a soil. The 

 farmer speaks of land as heavy or light, he may go further and 

 define his soil as a loam, a sandy clay, &c., but the mechanical 

 analysis reduces the relative proportions of sand and clay to 



B 2 



