M.—AGRICULTURE. 265 
with. Civilisation arose in the dry regions of the earth, and as far back as 
5,000 years ago irrigation was so advanced as a practical method that 
it came into the ordinances drawn up by the great Babylonian king 
Hammurabi. The chief problems at the present time are to discover 
effective means of economising water and to ascertain, and if possible con- 
trol, the relationships between the soil, the water, and the dissolved sub- 
stances in the water. Economical use of water is necessary because it 
allows larger areas to be irrigated, and because water beyond a certain 
amount injures the soil and asphyxiates the plant roots. This part of the 
problem is largely one of engineering and police control. The more serious 
problem, perhaps the most serious confronting agricultural science to-day, 
is that presented by the soluble matter in the water and the soil. The 
terrible spectre of alkali looms ahead of every irrigation project ; it may 
be kept under control for a longer or shorter time or it may completely 
wreck the scheme. Instances could be multiplied of schemes started with 
great expectations of results yet yielding only disappointment and loss. 
A volume could be filled with the tragedies of the alkali problem. Neutral 
salts, particularly sodium sulphate, are not harmful to plants unless their 
concentration exceeds a certain critical value ; indeed, some of the heavy 
soils in dry countries, as in Egypt and the Sudan, become unworkable if 
washed with pure water ; they remain flocculated only because some soluble 
salts are present. Chlorides beyond a critical concentration are more 
_ harmful to the plant, but sodium carbonate is deadly, and there is no 
: certain way at present of overcoming its effects. 
The empirical method has apparently gone as far as it can, and nothing 
more can be expected until some fresh opening is discovered by scientific 
workers. 
Almost equally important is the more efficient utilisation of water in 
districts where the rainfall is sufficiently high to obviate the need for 
irrigation, but insufficient to allow of any wastage of water. The practical 
work of the Utah agriculturists as exemplified by Widstoe, and the labora- 
tory results of Keen at Rothamsted, all indicate that something can be 
done. It is legitimate to hope that the next great advance will come from 
_ Canada, where in the West there are admirable opportunities for studying 
the problem. 
Inseparably bound up with water supply are the questions of cultiva- 
tion and of drainage, which affect not only the water but the air supply 
tothe roots. This former subject is now attracting considerable attention : 
the great need is to discover means for expressing cultivation in exact 
physical and engineering units. The measurements of Keen and Haines 
at Rothamsted, and the chemical work of A. F. Joseph, N. Comber, and 
others on clay, and of Odén, Page, and others on humus, indicate the 
possibility of finding exact expressions and of effecting co-operation with 
the workers in the new fields of agricultural engineering. 
Another soil factor which readily lends itself to some degree of control 
is the amount of plant nutrients present. The possibility of increasing this 
by means of manure has been so frequently explored in field trials that it 
has sometimes been regarded as almost a completed story; indeed, 
Rothamsted tradition affirms that Lawes himself once gave orders to have 
the Broadbalk field experiments discontinued because they had nothing 
further to tell; it was only the earnest persuasion of Gilbert that caused 
