Britain, the ruler of the greatest aggregation of Moslems in the world, of not depriving Turkey of a real independent existence. But the issue was complicated by many considerations, and British statesmen seemed less ready to accept his advice in peace than to use his influence in war. To the G.C.I.E. and the G.C.S.I. there was added in 1916 a salute of 11 guns and the rank and status of a first-class chief of the Bombay Presidency, the only previous instance of the grant of a salute outside the Indian territorial ruling families being that of the first Sir Salar Jung. (F. H. Br.)
AGLIARDI, ANTONIO (1832-1915), Italian cardinal and
diplomatist (see 1.377). Noted for his strongly patriotic sentiments,
he actively opposed the Temporalist tendencies which
prevailed at the Vatican during a part of the pontificate of Leo
XIII. At a time when clerical influences in France aimed at
a restoration of the Temporal Power, Agliardi was frankly
favourable to the Triple Alliance as the best guarantee of
Italy's territorial integrity, and he eventually succeeded in
convincing the Pope of the hopelessness of his schemes. With
Leo's subsequent social-Catholic activities he was in hearty
sympathy, and contributed much to their success. He enjoyed
the personal friendship of many of the most eminent men in
Italy, including Luigi Luzzatti, Antonio Salandra and the
Marquis di San Giuliano. He died in Rome March 19 1915.
AGRICULTURE (see 1.388). In the separate articles on
different countries of the world, their agricultural progress
between 1910 and 1920 is dealt with. Here will be considered
(i) the progress of scientific research generally, (2) the agricul-
tural administration and regulations in the United Kingdom,
and (3) the developments in the United Kingdom during the
World War. Developments in the United States 1910-21 are
described under the heading Agriculture in the article UNITED
STATES.
I. PROGRESS OF SCIENTIFIC RESEARCH.
During 1900-20 scientific research upon the soil was in the main directed to two sets of phenomena the interaction of the various groups of organisms living in the soil, and secondly the relation of the various soil constituents to water as a means of interpreting the physical behaviour of the soil under cultivation.
Soil Research. Dealing first with the latter question, it has long been obvious that the crude view which regards the soil as a mere mechanical foundation for the plant containing a certain amount of plant food nitrogen, potash and phosphoric acid determinable by analysis must be abandoned. Infertile soils disclose in the surface layer sufficient plant food for a hundred full crops, and even the later modification of the hypothesis which laid stress not on the " total " plant food in the soil but on the amount that was "available," i.e. soluble in some dilute medium such as carbon-dioxide-charged water and a solution of an organic acid akin to the cell sap of the plant, failed to provide a means of measuring fertility by chemical analysis. It was the failure of this chemical theory of the soil that led the American investigators, Whitney and Cameron, to propound the view that what really matters in the soil is its water relationships. The plant's roots feed in the soil solution, the liquid medium held on the surface of and between the soil particles by surface tension, and as this solution is always saturated, e.g. with phosphoric acid and potash of which any soil contains more than the soil solution is capable of dissolving, then the actual amount of these constituents in the soil (above a certain very low mini- mum) and the extra amount supplied by fertilizers are matters of indifference. Apart from some other factors, it is the water supply that determines the growth of the plant and therefore the fertility of the soil. In its turn this hypothesis breaks down, because it takes too simple a view of the process of solution in the soil, which it regards as a mixture of definite compounds possessing a definite solubility like sodium chloride or other inorganic salts. Actual experiment showed that whenever soil extracts were prepared from soils of different fertility or when even the solutions actually existing within the soils could be removed by mechanical means, they displayed a varying con- centration in phosphoric acid and potash. Moreover the growth
of plants in such extracts is, within limits, proportional to the amounts of the nutrient constituents they contain.
The value of Whitney's and Cameron's suggestion lay in the way it directed attention to the soil solution as the seat of nutrition of the plant, and our ideas as to the character and formation of that solution have to be revised in the light of our more recent conceptions of the nature of colloids. A study of the behaviour of any soil towards water, whether we examine such a character as the rate at which water will drain through the soil or the rate at which successive portions of water will be removed from it by evaporation under constant conditions, shows that the soil does not behave as if it were a mixture of mere rock particles of various grades of fineness. An artificial soil built up of particles of ground quartz of the same order of sizes as the soil behaves quite differently towards water, so again does a soil that has been ignited to a red heat. In the natural soil a number of the particles, especially those of the smallest size, exhibit colloid properties, which roughly means that they have a special power of holding water on their surfaces more and more tightly as the amount of water diminishes, and also of holding and withdrawing from solutions, the ions, sometimes basic, sometimes acid, of salts. These colloids are probably the particles of compound aluminium silicates resulting from the decomposition of the felspars in the original rock basis; they are akin to the zeolites which can be found in a pure state. The humus or organic matter of the soil is also largely colloid, but the inorganic colloids themselves will ac- count for most of the properties of the soil.
As regards the water itself, the colloid theory explains certain facts which had much occupied the attention of the American investigators who have been studying the relation of plants to soil under arid conditions as a means of extending cultivation upon the bad lands. Sachs had long ago shown that a plant would begin to wilt and be unable to take water from the soil before the soil was absolutely dry, again that a clay soil would hold water against the plant much more strongly than a sandy soil, wilting occurring when the clay soil has still 8 or more of water in it, whereas the sand will lose water down to I % before the wilting begins. Various attempts have been made to correlate the " wilting coefficient " of the soil, i.e. its proportion of moisture when wilting sets in, with the " hy- groscopic moisture," i.e. the amount of water a dry soil will absorb when in contact with a saturated atmosphere, and with the amount of water the soil holds when wetted and allowed to drain. But none of these conceptions mark any change of state; for example the curve expressing the rate at which evaporation will take place from soil is a perfectly smooth one without any discontinuities, and the points defining the wilting coefficient or the hygroscopic moisture are only particular positions of equilibrium between the water- holding power of the soil particles and the external set of forces tending to remove water. In the same way the distinction between the water held by the colloids and the " free water " in the soil, the latter being regarded as something different in kind and sharply marked off from the colloid water, cannot be maintained. The colloid " gels " must be regarded as imbibing water and exercising some attractive action on all the water in the soil, though that attraction is infinitesimal when the soil is saturated and only becomes a measurable force when the water has shrunk to small proportions.
The colloids that hold water in the soil are also the agents which control the composition of the soil solution upon which the plant feeds. If the soil colloids are brought into contact with a solution of any of the fertilizer salts (except the nitrates with which the action is very slight) there is an instantaneous absorption of ammonia, phosphoric acid or potash as the case may be, that is never complete, the extent being determined by such factors as the relative mass of the soil and the fertilizer, the concentration of the solution and the nature of the accompanying ions, e.g. carbon dioxide in the soil solution. Speaking broadly, a fertile soil is one possessing a high absorptive capacity, that is as it were pretty fully charged, so that the equilibrium with the soil solution is mobile and the soil colloids part freely with their nutrients to the solution as its strength is re- duced through withdrawals by the plant's roots. The analytical methods which attempt to determine say the " available " phos- phoric acid by attacking the soil with weak acids really determine something much more complex in which the absorptive power of the soil plays a part. The acid, whatever its nature, first dissolves all the phosphoric acid, and then there is a reabsorption, the amount of which is conditioned by the nature and strength of the acid em- ployed. Thus the result obtained is an empirical one, valid only for comparisons of soils of similar type and constitution, to which limited degree it is of service.
Lining Organisms. The study of the living organisms of the soil has resulted in some reconsideration of the views formerly held as to the relative importance and function of the different groups. Among the earliest of the organisms associated with the soil to be specifically studied were those concerned with the process of nitrification and responsible for the conversion of ammonia (resulting from the breaking down of organic compounds of nitrogen by other bacteria) first into nitrites and then into
