SECTIONAL TRANSACTIONS.—M. 515 
3. The reclamation of part of the Zuyder Zee. 
In this lake four polders will be made (total 225,000 hectares), equal in area to 
10 per cent. of the area now available for cultivation in Holland. One of these 
polders, the Wieringermeer polder (about 20,000 hectares) was already endiked at 
the end of 1929, the water being pumped out in 1930. 
4. Experimental Polder near Andijk. 
The soil of the new Zuyder Zee polders consists partly of sandy soils, partly of 
more or less clayey deposits, with little or no structure. The reclamation of the young 
Zuyder Zee clay polders is therefore quite a different matter from that of the young 
polders which were previously grass-grown kwelders. [or the study of this problem 
an experimental polder of 40 hectares was therefore made in the Zuyder Zee, near 
Andijk, in 1926-27. 
The soil of the greater part of this polder consists of a very clayey mass rich in 
calcium carbonate, with little humus and with 2-8 per cent. NaCl on dry matter. 
In 1927 the original muddy soil was very wet, containing an average of 172 gm. water 
per 100 gm. dry matter, without any structure, and being nearly impermeable to water. 
In order to be converted into normal soil this muddy mass has first to dry to 
acquire structure and to become permeable for water. In our humid climate a 
permeable soil rapidly loses its salts. The muddy mass of 1927, on an average 50 cm. 
thick and coloured black by FeS, with 172 gm. water and 2-8 per cent. NaCl per 100 gm. 
dry matter (approximately 16 gm. NaCl per litre soil water), had changed in two years, 
from 1927 to 1929, to a grey coloured, fairly dry upper layer, 20 cm. thick, with 
66 gm. water and only 0-2 per cent. NaCl per 100 gm. dry matter (approximately 
3 gm. NaCl per litre soil water), and a layer, about 23 cm. thick, from’20—-43 em., still 
in parts black and fairly wet, with 116 gm. water and 1-3 per cent. NaCl per 100 gm. 
dry matter (approximately 11 gm. NaCl per litre soil water). Meanwhile the original 
sodium clay soil, or rather the sodium magnesium clay soil, has to be changed into a 
calcium clay soil. Whereas the clay substance of normal Dutch polder soils contains 
an average of 79 Ca, 13 Mg, 2 K and 6 Na per 100 milligram equivalents of exchange- 
able bases, the muddy mass of the Andijk Experimental Polder contained, in 1927, 
about 24 Ca, 49 Mg, 8 K and 19 Na per 100 milligram equivalents. With good aeration 
the calcium carbonate comes into solution as calcium bicarbonate, which transforms 
the Mg-Na-clay into calcium clay. As this process is reversible, it is particularly 
important that the sodium bicarbonate formed should be led off. 
The main thing for the reclamation of the soil of the Andijk Experimental Polder 
was therefore a good drainage system. Very fortunately, the summers of the years 
1928 and 1929 were very hot and dry, so that the soil dried beautifully, large fissures 
and non-capillary pores appearing, the originally structureless soil acquiring in conse- 
quence a very good structure and a high permeability for water. 
5. Further investigations in the Wieringermeer polder. 
To permit of a further study of the extremely important problem of the drainage 
of the new Zuyder Zee soils, a drainage experimental field was laid out in the 
Wieringermeer polder, near Kolhorn, about 30 hectares in extent, where various 
drainage systems (ditches and drains) are being tested. In addition to the chemical 
values, the alterations in various physical soil figures, such as permeability, air-capacity 
(according to Kopecky) and volume-weight of the soil, are being studied. Some of 
the results of these tests and investigations will, it is hoped, be shown to those who 
attend the meeting of the Sixth Commission of the International Society of Soil 
Science, to be held at Groningen at the end of July 1932. They will then at the same 
time be able to see for themselves to what extent the cultivation of part of the 
Wieringermeer polder has been successful. 
AFTERNOON. 
ScIENCE AND THE PRopucTION or INDUSTRIAL CROPS :— 
RuBBER :— 
Mr. F. D. Ascor1.—Survey of the Present Position. 
Rubber as a commercial product is obtained almost solely from the Hevea 
Brasiliensis, which is not likely to be ousted by rubber-bearing bushes such as Guayule 
(America and Russia) and Chondrilla (Russia). 
1931 aye 
