512 SECTIONAL TRANSACTIONS.—M. 
new footing—a footing based on pedigree inspection of standing crops and a know- 
ledge of the precise geographical and regional range of usefulness of the various and 
increasingly large number of commodities which it will handle. 
Dr. E. M. Crowruer.—Improvements by Fertilisers. 
As the centenary of the British Association. almost coincides with that of the 
artificial fertiliser industry, the opportunity is taken to examine the development 
and the present position of the use of fertilisers and the method adopted in studying 
some of the practical problems of the present day. The production of the principal 
raw materials—Chilean nitrate, rock phosphate, crude potash salts and ammonium 
sulphate—expanded at surprisingly constant relative growth rates, especially during 
the interval between the agricultural crisis of the late ’seventies and the war. It 
happens that the phenomenally rapid expansion of the synthetic nitrogen industry 
during the war and again since 1923 has raised the total world supply to about the 
level which would have been reached if the pre-war rates had continued unchecked. 
Although obvious economic factors limit the use of fertilisers in individual areas, it 
would appear that the steady progress in consumption shown over long intervals is 
limited ultimately by the diffusion of the results of investigation and research. 
In the older agricultural countries there is a consistent movement towards 
increased proportions of nitrogen and potash, but this is balanced by the increased 
consumption of phosphoric acid in those newer countries which use little else. 
The rates of fertiliser consumption per unit of cultivated land are still extremely 
low except in a few special areas of intensive agriculture or large-scale market 
gardening, as e.g. in South Lincolnshire, Holland and the Atlantic Coast of U.S.A. 
The proportions of N, P,O;, and K,0 vary widely, and appear to depend more on 
political factors and proximity to supplies than on the inherent requirements of crops 
and soils. Thus, the relative effects of nitrogen and potash on crop yields are similar 
in East Prussia and Denmark, but the former uses five times as much potash per 
unit of nitrogen as the latter. Similar discrepancies are probably common, and 
have led on the Continent to an enormous output of work on the estimation of 
fertiliser requirements. There is a great need for co-ordinated schemes of field 
experiments on commercial farms to analyse present practice and to show the way 
to the more efficient use of fertilisers. Modern developments in the design and 
technique of field experimentation make it possible to obtain reliable results with 
little disturbance of normal farm operations. Experiments on the use of standard 
fertilisers under varied conditions are more needed than a multiplication of trials of 
closely related materials under uniform conditions. Some of the more ambitious 
experiments now being undertaken at experiment stations are reviewed. These 
include the study of the relationship of yield to the amounts of added nutrient, the 
dependence of response to fertilisers on weather, residual values over a period of 
years, differential responses of different varieties to fertilisers, the relationship of 
fertiliser effects to cultural conditions, and the development of a suitable technique 
for grassland experimentation. 
Dr. D. J. Hisstnx.—Improvements by Land Reclamation. 
1. Kwelders and sea-polders. 
By the recurrent tides muddy deposits are laid against the dikes of Holland until 
they are so high as not to be covered by the summer tides. The salts are then for 
the greater part washed out of the upper layer by the rain-water, so that a grass-flora 
makes its appearance. These grass-grown deposits are called ‘ kwelders’ (German : 
Groden); they are covered only by high tides, especially in winter. When the 
kwelder is high enough a dike is built to keep out the sea-water ; the kwelder becomes 
a polder. 
The soil of a young sea-polder, especially if it contains a large amount of clay, is 
extremely fertile. It is highly permeable to water, and nearly all the salts are washed 
out of the upper 50 cm. by the rain in the first winter after building the dike, so that 
the young polder is immediately ready for cultivation. 
2. The enclosure of the Zuyder Zee. 
A dike, 30 km. long, is being built from the coast of the province of Noord-Holland, 
by way of the island of Wieringen, to the coast of the province of Friesland, and will 
prapanly be completed by 1932, the Zuyder Zee being transformed from that moment 
into a lake. 
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