M.—AGRICULTURE. 259 
solution. Apparently, however, the colloids have a steadying or ‘ buffer- 
ing’ effect, reducing the degree of acidity caused by the production of acids 
and absorbing or precipitating various ions that might otherwise cause 
disturbances. 
A third important generalisation that has emerged is that the relations 
of the plant and the soil are not rigidly fixed but are capable of consider- 
able variation, being profoundly influenced by a third factor, the climate. 
A soil moderately fertile in one set of conditions may be relatively unpro- 
ductive in another. This happens repeatedly with soils containing much 
clay or much coarse sand. In Table I. are given the mechanical analyses 
of two soils, one of which, the Lias clay from England, is quite unworkable 
and remains derelict under our conditions of cool temperature and moderate 
but frequent rainfall, by reason of its high content of clay and fine silt ; 
while the other, which contains even more clay, is capable of carrying good 
crops of grain and cotton under the hot dry conditions of the Sudan. 
The Western prairie soil is of similar physical type to that of the English 
Weald soil, but while the prairie soil under its climatic conditions of warm 
dry summer and cold dry winter is, and is likely to remain, a fertile wheat 
producer, the Weald soil under the wetter conditions of England is less 
fertile. In hot dry conditions the clay is no disadvantage and may even 
be an advantage, but in wet conditions it becomes a serious drawback ; 
indeed, it might be possible to find some mathematical relationship between 
rainfall and degree of objectionableness in clay. 
TABLE I. 
Soils of similar type as regards mechanical analysis, but varying 
greatly in fertility by reason of climatic differences. 
Rich in finer fractions ire 
Waste P Poor a 
land very Fertile farmland Good Waste | Market 
difficult | Soul, difficult | PP! | Jand, | garden, 
of culti- | Millet & | ¢ culti-| 8° | Norfolk |Anglesey 
vation | Cotton vate | Wheat 
Lias clay| Weald | 29 35 i 
Oxford:| Sudan | clay, |Brandon| “<1” a rae 
shire Kent ste wea 
Coarse sand, 2:0 to 
0:2 mm. , : * 0-7 7-6* 1:5 2-5 62-4 93-7 
Finesand, 0:2to 0°04mm. 2-0 20-9 11-0 15-4 25:7 2-8 
Silt, 0:04 to0‘01 mm. . 64 |] 12-6 19-6 17:7 0-2 0-5 
Fine silt,0°01 to0:002 mm. 22:0 | J 26-8 16-1 1-8 0-4 
Clay (below 0:002 mm.) . 41-0 55:9 22-1 29-2 0-6 Nil 
* Mainly black nodules of calcium carbonate. 
It appears then that if a fertile soil were carried from one country to 
another its productive power would not necessarily be carried with it. 
Its fertility is, to a considerable extent, dependent on the fact that it fits 
in with the climatic factors in producing conditions favourable to good 
growth of desirable crops. 
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